The Gulf Stream by John Elliott Pillsbury is one of the classic works of modern oceanography. This work was first published as Appendix 10 of the Superintendent of the United States Coast and Geodetic Survey Report for 1890. The first three chapters of this work were devoted to the history of the exploration and study of the Gulf Stream from the time of the early European explorers to the year 1884. Pillsbury, a naval officer, undertook his famous studies from the Coast and Geodetic Survey Steamer BLAKE at that time and the remainder of The Gulf Stream was devoted to discussions of his instruments, methods and results. The first three chapters are reproduced in an abridged version here as Pillsbury was as meticulous in his historical studies as he was in his scientific work. These chapters provide a historical framework for the beginnings of modern physical oceanography as it includes the thoughts of 16th and 17th Century explorers and "cosmographers," Benjamin Franklin's work on the Gulf Stream, and the studies of numerous late 18th and early 19th Century scientists.
This work all preceded the first systematic oceanographic studies conducted by any nation, the Gulf Stream studies begun by the United States Coast Survey in 1844. Guided by Alexander Dallas Bache, naval officers commanding Coast Survey vessels led these early oceanographic expeditions. Bache, the second superintendent of the United States Coast Survey, set the formula for modern integrated oceanographic cruises by directing that physical oceanography, geological oceanography, and biological oceanography be incorporated into these pioneering cruises. Over the next 40 years, the Coast Survey continued pursuing knowledge of this great oceanic current. The efforts of the Coast Survey and the affiliated naval personnel associated with the early Gulf Stream studies did much to help lead the United States into the modern realm of oceanography.
Geography, the science that gives to us a knowledge of the earth's surface, is divided into two branches: first, all that pertains to the configuration, usually called geography, and second, everything relating to the natural forces acting thereon, called physical geography. These subjects are interlaced with the study of nearly every branch of human knowledge tending toward the good of the race in its struggle toward improvement. At first the pursuit of wealth by the discovery of new lands and peoples, brought about a study of the configuration of the surface, but little by little it was seen that the study also of the physical forces assisted toward this end and to the ease and comfort of mankind at large.
The Sun without doubt is the greatest factor in the support of terrestrial life, but this intense heat is tempered and governed by the elements, air and water, without which life as at present constituted on our globe would be unsupportable. The total area of the earth's surface is about 200,000,000 square miles, and of this only about one-fourth is land. The mean elevation of the land above the sea is less than 2,500 feet, while the mean depth of the ocean is probably about 12,000 feet. The total volume of the land above the sea level, therefore, is only about one twentieth of the volume of the ocean.
The surface of the ground quickly becomes heated by the direct rays of the sun, but it also quickly radiates its heat into the air, producing an aerial current. The surface of the water, on the other hand, absorbing the sun's heat, rapidly communicates it to the adjoining stratum, and, radiation from its surface being comparatively slow, its currents transfer the heat so acquired to distant points. The tempering influence on the climate is the wind, taking the heat and moisture from this heated water and transferring it to the land. It is argued most forcibly that such a stupendous change in the climatology of the world as existed during the glacial period was caused by the precession of the equinoxes and the change in the eccentricity of the earth's orbit effecting an alteration in the great heat distributors, the ocean currents.
To commerce and navigation the study of these currents is of the utmost value. The length of the voyage is shortened, and the chance of safety to vessel, cargo, and lives is increased. A strong wind against a current produces a dangerous sea, and, by a knowledge of the laws of the water's flow, a vessel, by a trifling change of course, may escape the danger.
Zoological geography may consider them [ocean currents] as highways which unite the zones of the ocean, and consequently cause the dissemination of species, and at the same time by the intensely progressive attenuation of salt and the temperature of these waters this highway facilitates the evolution of species. It is thus that the currents enter into the question so important to origins, monogenism, or polygenism.
Anthropology, for example, holds them responsible for the solution of the great problem, that of human migrations, which spread even to the distant archipelagos the different varieties of the race man, at the time when there was scarcely a discernible difference between man and beast, and he had at his disposal only rudimentary means for struggling against the brute forces of nature.
Botany and zoology ought to be interested in our researches, for the conditions of organic life in all its bearings are governed by these currents either warm or cold, which give to subterranean regions a veritable climate; and it is perhaps owing to certain disturbances which have taken place in the volume, direction, and temperature of these currents that the almost entire disappearance of several kinds of migratory fish is attributed, as, for example, that of the sardines, which formerly lined the coasts of France in countless numbers.
It concerns geology also, for the oceans receive a deposit, the organic and mineral detritus which the winds and waves bring to it, the stones which the glaciers wrest from the polar regions and which the icebergs carry to the temperate regions. The sea currents charge themselves with distributing all these minerals according to certain laws, and in this manner collections are formed which in later times convulsions of the earth bring to light.
Paleontology itself ought to be interested in our researches, for is it not evident that the rivers, drifting dead bodies across the continents, deposit them on sand banks far from their habitat to become the fossils of the future?
There is another reason for studying these currents which will ultimately have the most beneficial influence on mankind. It is now known that the currents vary through certain forces acting upon them, by periodic changes, entirely according to law, and again through apparently erratic forces. Probably every motion of these vast bodies is absolutely governed by laws which can be ascertained. The moisture and varying temperature of the land depends largely upon the positions of these currents in the ocean, and it is thought that when we know the laws of the latter we will, with the aid of meteorology, be able to say to the farmers hundreds of miles distant from the sea, "you will have an abnormal amount of rain during next summer," or "the winter will be cold and clear," and by these predictions they can plant a crop to suit the circumstance or provide an unusual amount of food for their stock. We will be able to say to the mariner, at such time the current will be so much an hour in such a direction, and the percentage of error will be but trifling. From a study of these great forces, then, we derive our greatest benefits, and any amount of well-directed effort to gain a complete mastery of their laws will revert directly to the good of the human race.
In the Atlantic Ocean the currents are probably more pronounced than in either the Pacific or Indian Oceans. Without entering upon a discussion at this point as to the causes of ocean flow or of any particular current, a brief description of the main streams will not be out of place, for they are all connected more or less intimately with our own Gulf Stream. The equatorial current is usually described as being a broad band of water moving slowly across the Atlantic in the tropics. The portion situated south of the equator is divided into two parts upon meeting the resistance of Cape St. Roque, the eastern salient point of the South American coast. One branch turns to the southward toward the Antarctic, and the other is forced to the westward along the shores of Brazil and Guyana. This branch is called the Guyana coast current. The equatorial current has north of the equator an almost uninterrupted progress until it reaches the Windward Islands, but a portion of it impinges against the South American coast and perhaps increases the volume of the northern branch of the south equatorial current. At the Windward Islands all are united, and a portion of the water enters the Caribbean to assist in forming the Gulf Stream. Between the northern and southern portions of the equatorial current is the Guinea current, setting toward the east and southeast into the Gulf of Guinea. It was formerly thought to be a continuation of the North African current, "but later investigation," Findlay says, "seems to point to the fact that it is a flowing back of the waters heaped up to the westward by the prevalent winds." It seems to run strongest in the summer months, when it is felt as far west as longitude 45o, while in the winter it reaches only as far as the twenty-third meridian. In the Northern Atlantic Ocean the Labrador current sweeps down from the Arctic along the eastern shores of Greenland and from Baffin's Bay and passes the coasts of Labrador and Newfoundland, bearing with it vast fields of ice and enormous bergs. Reaching the Gulf Stream, it is said to underrun the latter, and also in part form a counter-current to the southward along our coast as far south as Cape Hatteras, or even to Cape Canaveral.
The Gulf Stream, the grandest and most mighty of any terrestrial phenomenon, receives its waters from the Caribbean Sea through the Straits of Yucatan. It is commonly said that a portion doubles Cape San Antonio and enters the Straits of Florida at once, while another part, after making the tour of the Gulf of Mexico, joins the first in its flow to the northward. Its waters are characterized by a deep blue color, great clearness, and high temperature. The eye can penetrate it to considerable depths, and frequently its meeting with the colder water from the polar regions can be at once distinguished.
It is difficult for the mind to grasp the immensity of this great ocean river. The observations taken at its narrowest point were between three and four thousand in number, surface and subsurface, and a calculation of the average volume passing Cape Florida in one hour gives the enormous sum of 90,000,000,000 tons. If this one hour's water were evaporated, the remaining salt would require more than one hundred times the number of sea-going vessels now afloat in the world to carry it. That this wonderful body is governed by law in all its motions there can be no doubt. It has its daily and monthly variations in velocity, direction, and temperature, changing with as perfect regularity as the tides in a harbor. Nor do I doubt that it has also a yearly fluctuation, and perhaps others occupying a cycle of many centuries to complete.
The Gulf Stream after leaving the Straits of Florida pursues a general northeasterly direction, pressing close to Cape Hatteras, passing between Bermuda and Nova Scotia, and as a defined and permanent stream is soon afterwards lost. Currents are found in the vicinity of the Azores Islands setting about southeast, and also on the coast of Africa setting south, which are sometimes called the southeast extension of the Gulf Stream. Warm water is found off the coasts of Ireland, Scotland, and Norway, giving evidence of a tropical flow, and this is called the northeast extension of the Stream. Whether or not these currents are wholly formed of the water issuing from the Straits of Florida remains to be discussed later.
Man stands with bowed head in the presence of nature's visible grandeurs, such as towering mountains, precipices, or icebergs, forests of immense trees, grand rivers, or waterfalls. He realizes the force of waves that can sweep away light-houses or toss an ocean steamer about like a cork. In a vessel floating on the Gulf Stream one sees nothing of the current and knows nothing but what experience tells him; but to be anchored in its depths far out of the sight of land, and to see the mighty torrent rushing past at a speed of miles per hour, day after day and day after day, one begins to think that all the wonders of the earth combined can not equal this one river in the ocean.
General Historical Account Of The Gulf Stream
Before the time of Columbus's grand discovery of the New World the coasting vessels of the Old must have recognized that there were currents in the Atlantic Ocean which were entirely independent of the tides; but the first indication that currents on the coast of North America were noticed is found in the writings of the Northmen in their description of voyages to America. Several suggestive names were given to prominent objects of discovery, such as Straumsoe (Isle of Currents), Straumsfjorde (Bay of Currents), and Straummes (Cape of Currents), but their exact location can not be identified. Some claim that the voyages extended even to Florida, but it seems probable from later investigations that the points named were all in the vicinity of Cape Cod.
Columbus, before undertaking his voyage of discovery toward the west, resided for some time on the island of Porto Santo, and it was here that he was shown a piece of curiously carved wood that had evidently drifted there from other lands. Strange woods and other floating objects were continually being thrown upon shores of Norway, Scotland, and Ireland, all of which, to a thoughtful mind like that of Columbus, must have induced the belief that there were other lands at no great distance to the west, and so it is probable that to the Gulf Stream in part the world owes the discovery of America.
In actual observations in the Gulf Stream, or rather in the currents contributing to it, Columbus was the pioneer. It is related that September 19, 1492, he sounded with a deep-sea line, and the lead, passing through the surface drift into the dead water below, showed at once that there was a current setting his vessels to the southward and westward. On his subsequent voyages he remarked the strong currents of the Caribbean Sea. He says, for example, " When I left the Dragon's mouth" (the northern entrance to the Gulf of Paria) "I found the sea ran so strangely to the westward that between the hour of Mass, when I weighed anchor, and the hour of Complines, I made 65 leagues of 4 miles each with gentle winds." He also says of the currents entering the Caribbean between the Windward Islands, "I hold it for certain that the waters of the sea move from east to west with the sky, and that in passing this track they hold a more rapid course, and have thus carried away larger tracts of land, and that from hence has resulted the great number of islands."
On his fourth voyage Columbus discovered and noted the strength of the current on the coast of Honduras, although it is probable that at this time the Gulf Stream itself in the Straits of Florida had been found by independent navigators. Peter Martyr says "he left in wryting that sailing from the Island of Guanassa toward the east he found the course of the waters so vehement and furious agaynst the fore part of his ship that he could at no time touch the ground with his sounding plummet, but that the contrary violence of the waters would bear it up from the bottom. He affirmeth also that he could never in one day with a good wynde wynn one mile of the course of the waters.
Columbus speculated as to the cause of these currents. He thought that the equatorial waters followed the motions of the heavens about the world--that is, the rotary motion by which the stars and air revolve about the globe (as was the opinion of the time), so also the water was supposed to partake of the same motion.
John and Sebastian Cabot, in 1497, crossed the North Atlantic Ocean, rediscovering the coast of Labrador. From this point they steered to the southward and westward, "so coasting still by the shore that he was brought so far into the south by reason of the land bending so much to the southward that he was then almost equal in latitude to the sea called Fretum Herculeum, having the north pole elevate in manner in the same degree. He sayled likewise in this track so far toward the weste that he hadde the Island of Cuba in his left hande in manner in the same degree of longitude." * * * "He sayeth that he found the like course of the waters towarde the west, but the same to run more softly and gently then the swift waters which the Spanyards found in their navigation southward."
It is probable that the Cabots did not double Cape Hatteras and discover the Gulf Stream. It is thought by some that they entered the Straits of Florida, but from the testimony of Peter Martyr, quoted above, they were north of Hatteras and probably in the vicinity of the Delaware, but in the longitude of Columbus's discoveries in the West Indies. They did, however, notice the fact that a gentle counter current existed.
The Cortereals, between 1500 and 1502, on several voyages extending from Labrador toward Cuba, probably crossed the Gulf Stream and may have recognized its strength, but very little is known as to the exact localities visited.
In the year 1508 the Island of Cuba was for the first time circumnavigated. Sebastian de Ocampo, under the authority of the Governor of Hispaniola, sailed along the northern coast of the island through the old Bahama Channel and around the western point, Cape San Antonio. In this voyage eight months were occupied, and as it was against the Gulf Stream it would seem that he must have noticed it. As the times demanded however the custom of secrecy on all expeditions, no record has been left of the fact.
The first record, on which the evidence is satisfactory, of the discovery of the Gulf Stream current, is that of Ponce de Leon in his expedition in 1513 in search of the fountain of youth. In company with the afterwards famous navigator, Antonio de Alaminos, he sailed from Porto Rico, along the northeastern side of the Bahamas, and crossed the Gulf Stream somewhere above Cape Canaveral. After reaching a latitude of about 30o north he turned and skirted the coast as far as Tortugas, thus stemming the current for a distance of several hundred miles. Referring to these currents, their journal says that they saw a current which, though they had a good wind, they could not stem. It seemed that they were going through the water fast, but they soon recognized the fact that they were being driven back and that the current was stronger than the wind. Two vessels, which were somewhat nearer the coast, came to anchor; the third vessel, a brig, being in deeper water, could not anchor, and was soon "carried away by the current and lost from sight although it was a clear day." Ponce de Leon, on this expedition, crossed the stream no less than four times, and Alaminos received his first apprenticeship in its navigation, which in after years proved to be of great benefit to him.
During the next few years the Spaniards crossed and recrossed the Stream between Cuba and Florida many times in their search for gold, and of course gained much practical knowledge of the strength and velocity of its currents.
It is interesting to note the speculations of the day as to the cause of this startling phenomenon, and its result on the sailing route to Europe. The which, while I consider I am drawn into no small ambyguetie and doubt, whyther those waters have their course which flowe with so continual a tract in the circuite from the easte, as though they fledde to the weste never to retourne, and yet neyther the weste thereby any whit more fylled nor the east emptied.
If we say that they fall to their centre (as in the nature of heavier things) and assign the equinoctial hyll to be the centre (as some affirme), what centre shall we appoint to be able to receive so great abundance of water, or what circumference shall be found wet.
Many think that there should be certayne large strayghts or entrances in the corner of that great land which we describe to be eight times larger than Italie, and the corner of that land to be full of gulfes, whereby they suppose that some strayghts should pass through the same lying to the weste side of the Island of Cuba, and that the said strayghts swallowe up those waters and so conveys the same into the weste, and from thence again into the easte ocean or north seas as some think. Others will, that the Gulf of that great lande, be closed up and the lande to reach far to the north in the back side of Cuba, so that it embrace the north landes which the frozen sea encompasseth under the north pole, and all the lande of these coasts should joyne together as one firme lande. Whereby they conjecture that these waters should be turned about by the object or resistance of that lande so tending toward the North, as we see the waters turned about the crooked banks of certayne ryvers. But this agreeth not in all points, for they also who have searched the frozen sea, and sayled from thence into the weste doe likewise affirme that those north seas flowe continually toward the weste although nothing so swiftly. * * * Wherefore it is not only more likely to be true but also of necessity to be concluded, that between both these landes hitherto unknown, there should be great certayne open places whereby the waters should thus continually passe from easte into the weste, which waters I suppose to be driven about the Globe by the incessant moving and impulsion of the heavens, and not to be swallowed up and cast out again by the breathing of Demo-gorgon as some have imagined, because they see the seas increase and decrease, flowe and reflowe. The same writer continues at a later date:
Let us now therefore speake somewhat again of the later news and opinion as concerning the swift course of the sea toward the weste about the Coast of Paria. So it is therefore that Andreas Moralis, the pilot, and Ouidas (of whom we have made mention before) repayred to me at my house in the time of Matrite. As we met thus together there arose a contention between them two as concerning this course of the ocean. They both agree that these landes and regions pertayning to the Dominion of Castile, do with one continuale tract and perpetual bond embrace as one whole firme lande or continent all the mayne lande lying to the north of Cuba and the other islands, being also northwest from both Cuba and Hispaniola. Yet as touching the course of the waters they vary in opinion; for Andreas will, that his violent course of the water be received into the lappe of the supposed continent, which bendeth so much and extendeth so farre toward the north, as we have said, and that by the object or resistance of the lande so bending and crooking the water as it were, rebounde in compasse and by the force thereof be driven about the north side of Cuba and the other islands excluded outside the circle called Tropicus Cancri, where the largeness of the sea may receive the waters falling from the narrow streams and thereby represse that inordinate course by reason that the sea is there very large and great.
The Admiral himself, Diegas Colonus, sonne and heyre of Christophorus Colonus the first finder of these landes, being demanded of me what he found or perceived in sayling to and from, answered that there was much difficultie in retourning the same way by which they go; but whereas they first take their way by the mayne sea toward the north before they direct their course to Spayne, he sayth that in that tract he felt the shippe sometymes a little driven back by the contrary course of the waters yet supposed that this chaunceth only by the ordinary flowing and reflowing of the sea, and the same not to be enforced by the circumflection of the water rebounding in compass as we have sayde; but thinketh that this mayne lande or supposed continent should somewhere be open.
Ouidas agreeth with Andreas Moralis as touching the continual adherence of closeness of the sayde continent, yet neither that the water shoulde so beat agaynst the bending back of the weste lande, or be in such sort repulsed and driven into the mayne sea; but sayth that he hath diligently considered that the waters runne from the deepest and wyddest of the mayne sea toward the weste. Also that sayling near into the shore in small vessels, he found the same waters retourne agayne toward the east, so that in the same place they runne together with contrarie course.
Thus have we made you partner of such things as they have given us and written their divers opinions. We will then give more certayne reasons when more certayne truth shall be known. We must in the meantime leane to opinions until the day come appointed of God to reveal this secret of nature with the perfect knowledge of the pointe of the pole Starre. It is certainly most remarkable, when we consider how imperfect was their knowledge of the form or extent of the continent, that their views should have been so near the truth. The Gulf of Mexico was not discovered until 1517, and explored the year after, when the current on the western of the Straits of Yucatan must have been found. Ocampo, in circumnavigating Cuba, judging from experience of the present day, could have found only the tidal currents in the vicinity of Cap San Antonio. The current in the passages in the eastern Caribbean was known to be strong and westerly, and on the Honduras coast the same. Alaminos and Ponce de Leon had found the current in the Straits of Florida, and evidently some of the speculators determined that the land was continuous and in some way the two parts of the flowing stream of water were connected.
Antonio de Alaminos was without doubt the most experienced navigator and pilot in the West Indian waters. He had been chief pilot with Columbus on his last voyage, had been with Ponce de Leon around and among the Bahamas and along the coast of Florida from St. Augustine to Tortugas, and had crossed and recrossed the stream several times. He had afterwards been with Cordova and Grijalva exploring the coast of Yucatan and the Gulf of Mexico. He was familiar with the fact that there was a passage north of Cuba from Gulf to the Ocean, but beyond the Straits to the northward was unknown to him. He thought, however, as Herrera says, "that these mighty currents ought to empty somewhere into an open space." Upon fitting out the expedition for the conquest of Mexico, Cortez gave the chief command of the fleet to Alaminos, and when, later, it was thought necessary to send dispatches and presents to Spain, he was given the fastest vessel to carry the Envoys. Instructions were given him to hold his course north of Cuba and pass into the Atlantic through the Straits of Florida, not touching at any port in the West Indies. Probably this route was suggested to Cortez by Alaminos as being most favorable for a quick passage, and one by which he would be sure to avoid a chance meeting with an enemy either of his own or of a foreign country. The vessel sailed from Vera Cruz July 26, 1519, and after disobeying his instructions by making a stop at the port of Marien on the north side of Cuba, Alaminos passed through the Straits of Florida and reached Spain in safety. It is of course doubtful how far he followed the Gulf Stream, but it is probable that he did so well up the coast toward Cape Hatteras. His voyage changed the course of navigation from the West Indian ports and contributed largely toward the growth of Havana. This port soon became the rendezvous of the West Indian trading fleet, the distributing point of goods from Europe, and the starting port for the return home.
During the half century following the remarkable voyage of Alaminos, there were expeditions without number to the West Indies and the mainland, and while there are minute and detailed descriptions of the land, products, and people, yet scarcely anything is said of the sea currents.
Sir Humphrey Gilbert, writing before 1576, says that all the waters of the ocean "run by nature circularly from east to west, following the diurnal motions of the Primum Mobile." He traces the motions of the waters from the south of Africa and says that from there it strikes over to America. Not finding free passage "it runs all along the eastern coast of that continent northward as far as Cape Freddo, being the farthest known place of the same continent toward the North, which is about 4,800 leagues." He thinks that even if this current has not been traced all along the coast of America, "still it must exist either in uppermost or the nethermost part of the sea." For the reason that this current must have a free passage somewhere Gilbert says "it must either flow around the north of America into the South Sea or it must needs strike over upon the coasts of Iceland, Norway, and Finmark." He adopts the first of the alternatives, as he is anxious to prove the existence of the Northwest Passage. In the journal of his last voyage he mentions that in 50o north latitude they saw ice being carried to the southward, and so conjectured that a current must be setting in that direction. In 1579 and again in 1583 he made two unsuccessful attempts to establish colonies on the east coast of the present United States, and it is curious to see how great was the influence of the Gulf Stream, even at that time, in directing navigation. In considering the advisability of taking the southern passage from England or the more direct but more difficult northern one, he says, "by what way to shape our course, either from the south northward, or from the north southward. The first course, that is, beginning south, without all contraversie was the likeliest wherein we are assured to have commoditie of the currents, which from the Cape of Florida setteth northward, and would have furthered greatly our navigation, discovering, from the foresaid cape toward Cape Breton and all these lands lying to the North." The advantage of being able to provision the vessel at the Banks of Newfoundland led them to decide upon the northern route "although contrareity of currents descending from the Cape of Florida into Cape Breton and Cape Race would fall out to be great and irresistible impediments unto our further proceeding for that year, and compel us to winter in those northern regions."
The records of the voyages of Martin Frobisher are of great interest as showing the gradual extension of knowledge on the subject of ocean currents. He crossed the northern Atlantic six times during the years 1576-'77-'78. In the account of this third voyage he says: Sayling toward the northwest parts of Ireland we mette with a great current from out the southwest, which carried us [by our reckoning] one point toward the northeastward of our said course, which current seemed to us to continue itself toward Norway and other of the northeast parts of the world, whereby we may be induced to believe that this is the same which the Portugese mette at Capo de Buong Speranza [Cape of Good Hope], where, stricking over from thence to the Straits of Megellan and finding no passage there for the narrowness of the sayde Straits, runneth alongue to the great Bay of Mexico, where also having a let of land it is forced to strike back again toward the northeast, as we not only here but in another place also further northward by goode experience this year have found. How the currents returned to the Cape of Good Hope from the "northeast parts of the world" is not stated, but the general course of the Atlantic system is very fairly laid out.
About this time there appeared the theory in "La Cosmographie" that the currents in the Straits of Florida were caused by the rivers emptying into the Gulf of Mexico, and this theory has been held by writers at much later dates. In 1596 it is recorded by D. Layfield, chaplain of the Earl of Northumberland, that between Bermuda and the Azores they thought they observed a current,but shortly before arriving at the latter they were sure of a current setting southward.. The next expedition to that of Gilbert, for settling Virginia and North Carolina, was under Captains Amadas and Barlow. They took the southern passage, as did also all of those under Raleigh. Some of these left the Caribbean east of Cuba, and others continued to the westward and passed through the Straits of Yucatan and Florida.
In 1590 John White, who had been Governor of the colony at Roanoke, referring to the portion of the voyage from Florida Keys to Virginia, says: "We lost sight of the coast and stood to sea for to gaine the helpe of the current, which runneth much swifter farre off than in sight of the coast, for from the Cape of FLORIDA to Virginia, all along the shore, are none but eddie currents setting to the south and southwest." This is the first instance in which there is indicated a knowledge of an approximate position of the axis of the Stream.
In 1606 an observation is recorded by Lescabot, which is evidently a meeting of the Labrador and Gulf Stream currents. He noticed that while in latitude 45o and "six times 20 leagues to the eastward of the Banks of Newfoundland, we found for the space of three days the water very warm, whilst the air was cold as before, but on the 21st of June quite suddenly we were surrounded by fogs and cold that we thought to be in the month of January, and the sea was extremely cold." He attributes this to the ice from the north which comes floating "down from the coast and sea adjoining to Newfoundland and Labrador, which is brought thither by the sea in her natural motion."
The influence of the Gulf Stream in the colonization of North America was about this time very great. In 1606 the English divided their possessions into two parts, the northern part of Virginia (new England and vicinity) was one, and the present North Carolina and Chesapeake Bay region the other, and for each a company was established and commissioned by the King. The route used in going to the first was that tried in 1602 by Capt. Bartholomew Gosnold, crossing the Atlantic on about the fortieth parallel, while the southern expeditions held the old passage through the trades and Caribbean. The Dutch vessels bound to New York adopted the West Indian route, so that Nantucket really became the dividing line of travel, and a difference in destination of a degree in latitude necessitated a difference of thirty degrees in route. This seems only to be accounted for by the real or imaginary assistance of the winds and currents in one and the impediment of the Stream in the other. After the English and Dutch settlements became firmly established and crossing the Atlantic a common thing, the personal experience of navigators was no longer thought to be of sufficient importance to print, and the time had not yet arrived for adopting a plan of collecting ship's journals and publishing such nautical information from them as would be of value to others. The writers on the subject, however, must have had access to these journals and corrected and improved their ideas on the subject of currents, and in the latter half of this century many works on hydrography appeared.
In 1650 Varenius gave the most complete description of currents which had been issued up to this time. He classified them into perpetual and periodical, special and general. The system of which the Gulf Stream forms a part he placed as a perpetual special motion of the sea, and describes it as a gigantic Stream beginning at the eastern Capes of Brazil, flowing from south to north and ending toward Florida. He adds, "a similar current from south to north is observed along the Philippine Islands and toward Japan." He also wrote that "some Copernicans, as for instance Keppler, pretend that also the movement of our globe contributes not a little toward it" (the currents), "because the water, not being adherent to the earth but only in a loose contact with it, cannot follow the quickness of its motion toward the east, but is left behind toward the west, so that the sea does not move from one part to the other, but on the contrary it is the earth which quits or leaves the parts of the sea, one after the other."
In 1663 Isaac Vossius wrote a work entirely devoted to the motion of wind and sea, and in it particularly describes most of the currents known in the present day. He says:
With the general equatorial current, the waters run toward Brazil, along Guyana, and enter the Gulf of Mexico. From there, turning obliquely, they pass rapidly through the Straits of Bahama. On the one side they bathe the coasts of Florida and Virginia and the entire shore of North America, and on the other side they run directly east until they reach the opposite shores of Europe and Africa; from thence they run again to the south and join the first movement to the west, perpetually turning in this manner circuitously. He emphasizes this by saying that "a ship without sails and sailors might be conveyed solely by the force of the currents from the Canary Islands to Brazil and Mexico, coming back from there by way of the Florida stream toward Europe on a route some 4,000 German miles in length." Vossius's theory as to the cause of the ocean circulation was that the heat of the tropical sun attracted the ocean and at the same time increased its bulk and formed, as it were, a long mountain of water, "to which the vessels even have some difficulty in ascending when they sail toward the line." He concluded that the sun carried this mountain of water toward the South American shore, where it broke and ran along the coasts. A French hydrographer, George Fournier, some years later propounded a theory almost the opposite. It was that the sun evaporated enough water in the tropics to make a deep valley, and therefore the water from the poles was forced to run toward the equator along the coast of Africa to replace the lost water. He though that the depression always ran before or with the sun and the arriving polar water behind the sun and the rotary system of currents was thus produced.
In 1678 Athanasius Kircher, a Jesuit, gave to the world in his "Mundus Subterraneus," the first published chart showing the system of ocean circulation and the Gulf Stream. He says of the causes of the Gulf Stream:
This motion touches many things, whether partly from the general motion of the trade winds against the opposing shores of that region and thence again reflected, which they call the Sailor's Current, or from wind-storms, or finally from the flow and the reflow caused by the moon's force. He was, however, a strong believer in submarine abysses as the cause of vortices and special currents. In 1685 a German named Happelius published another chart of Ocean currents
quite similar to Kircher's. In his work he says:
The general motion of the Ocean goes from east to west, and it is most obvious in the torrid zone. The sun is the cause of this general course of the sea as well as of the trade winds. The particular motions of the sea are of two kinds, one on a straight line and the other with a circulating or whirling movement. Of those which run in a straight line some are constant, regular, and perpetual the whole year through. Some show themselves only at times and change even in direction, are irregular, depending much on the direction of the wind. In the Atlantic from the Brazilian Cape to St. Augustine toward the Antilles and Florida is a constant and perpetual course of the sea from the south to north. About this time the question began to be agitated in the minds of scientists as to how the strange fruits and woods were deposited on the shores of Ireland, Scotland, and other northern lands. The molucca bean was frequently found there, and the fact was thought to be proof of either a northeast of northwest passage to the East Indies. In 1696 Dr. Hans Sloan proved that these beans came from Jamaica. He says:
It is very easy to conceive that, growing in Jamaica, and having got to sea by the rivers, they may be carried by the winds and by the current which is forced through the Gulf of Florida, going there constantly east into the North American Sea; but how they should come the rest of their voyage I can not tell, unless it be thought reasonable that the beans, being brought north by the current from the Gulf of Florida, are put into the westerly winds' way, and may be supposed by this means at last to arrive at Scotland. This is exactly the opinion of many people at the present day.
In 1702 and again in 1720 the fact was stated that the Gulf Stream ran the strongest in the Straits of Florida during strong northerly winds, and as an explanation of this phenomenon Professor Leval thought that it could only be accounted for by the supposition that during the north winds in the channel in the Gulf of Mexico they were blowing from a more northwesterly direction, and in this was pushed the waters of the Gulf into the Straits and so forced them through the latter with increased velocity. The French route from Louisiana to Europe followed the Gulf Stream along the North Atlantic coast toward the Banks of Newfoundland, differing considerably from the more southern route taken by the Spaniards, but while adopting this most expeditious track they went to the other extreme in sailing from their Gulf to their West Indian possessions. They followed the Stream well up toward the Grand Banks, then south to the trade winds and west to their port.
Up to this time, with the exception of Kircher and Happelius in 1679 and 1685, there seems to have been no attempt to indicate the Gulf Stream upon the charts, and even these were more for scientific interest than for the practical benefit of mariners. One chart published in 1630 by the Earl of Northumberland gave the words "Corrento verso Greco," placed about half a degree from Cape Hatteras; but with this exception up to the first half of the eighteenth century, charts generally only show an inscription between Cuba and Florida, "Canalis Bahama versus Septentrionem semper fluit," or its translation into other languages. About the middle of the eighteenth century arrows appeared on the charts of the British colonies to indicate coast currents, and at the same time French charts indicated currents in the Caribbean and in the Straits of Florida in like manner. In 1772 detached indications of the Gulf Stream currents appear, and in 1775 on a special map of Carolina there are arrows near the coast pointing to the southward and westward, and farther off the coast pointing North.
That the want of knowledge as to the limits of the Stream was felt is shown by the length of time consumed in passages between the same ports in opposition directions. A voyage from Boston, Massachusetts, to Charleston, South Carolina, would sometimes take three or four weeks, while a return trip would frequently be made in one week. The coasting captains and whalemen, however, were gaining experience regarding the Stream, and to the latter more than all others, up to the time of the Revolutionary War, Franklin was indebted for the information which led to the publication of his chart of the great Ocean current.
These whalers extended their search as far south as Bahama and as far east as Newfoundland, or even to the longitude of the Azores. They discovered that the whales appeared to the north of a certain line and to the south of another line, and were but rarely seen between the two, and these lines they concluded were the limits of the Gulf Stream. The whale fishery soon became the school for American navigators, particularly of New England vessels, and in this way knowledge of the Gulf Stream was introduced into the commercial traffic of the times. The American shipmasters, from their superior information on the subject of currents, inaugurated a change in the sailing route from Europe, by which they could save two weeks or more in the passage. From England they crossed the Newfoundland Banks in about latitude 44 and 45 degrees, and thence on a course inside the limits of the Stream.
Gulf Stream Investigations From The Time Of Franklin To Those Made By The U.S. Coast Survey
How long the American fishermen had been acquainted with the secret of the Gulf Stream's peculiarities before it was brought to the notice of Franklin it is impossible to state. They kept the secret, however, until, as Franklin says--
About the year 1769 or 1770, there was an application by the Board of Customs at Boston to the Lords of the Treasury at London, complaining that the packets between Falmouth and New York were generally a fortnight longer in their passage than the merchant ships between London and Rhode Island, and proposing instead of New York that for the future they should be ordered to Newport.
Being then concerned in the management of the American Post-Office, I happened to be consulted on the occasion, and it appearing strange to me that there should be such a difference, especially when the merchant ships were generally deeper laden and more weakly manned than the packets, and had from London the whole length of the river and channel to run before they left the land of England, while the packets had only to go from Falmouth, I could not but think the fact misunderstood or misrepresented.
There happened then to be in London a Nantucket sea captain of my acquaintance, to whom I communicated the affair. He told me he believed the fact to be true, but the difference was owing to this, that the Rhode Island captains were acquainted with the Gulf Stream, while those of the English packets were not. "We are well acquainted with that stream, because in our pursuit of whales, which keep near the sides of it but are not met within it, we run along the side and frequently cross it to change our side; and in crossing it have sometimes met and spoke with those packets who were in the middle of it and stemming it. We have informed them that they were stemming a current that was against them to the value of 3 miles an hour and advised them to cross it, but they were too wise to be councelled by simple American fishermen. When the winds are light," he added, "they are carried back by the current more than they are forwarded by the wind, and if the wind be good the subtraction of 70 miles a day from their course is of some importance."
I then observed that it was a pity that no notice was taken upon the charts, and requested him to make it out for me, which he readily complied with, adding directions for avoiding it in sailing from Europe to North America. I procured it to be engraved by order from the General Post-Office on the old chart of the Atlantic, at Mount & Page's, Tower Hill, and copies were sent to Falmouth for the captains, who slighted it, however, but it has since been printed in France, of which edition I hereto annex a copy.
Franklin's theory on the subject of the cause of the Gulf Stream is given in the same report.
This stream is probably generated by the great accumulation of water on the eastern coast of America between the tropics by the trade winds which constantly blow there. It is known that a large piece of water, 10 miles broad and generally only 3 feet deep, has, by a strong wind, had its water driven to one side and sustained so as to become 6 feet deep, while the windward side was laid dry. This may give some idea of the quantity heaped upon the American coast, and the reason of its running down in a strong current through the islands into the Bay of Mexico and from thence proceeding along the coasts and banks of Newfoundland where it turns off towards and runs down through the Western Islands. Franklin did not press his new chart on the notice of the English ship captains after they had once rejected it, but for the time being suppressed it, for political reasons, until the conclusion of the War of Independence. In the mean time, in 1775-'76, and in later years, whenever he made a voyage across the Atlantic, he took observations of the surface temperature of the Ocean.
I find that it [the Gulf Stream] is always warmer than the sea on each side of it, and that it does not sparkle in the night. I annex hereto the observations made in two voyages and may possibly add a third. It will appear from them that the thermometer may be a useful instrument to the navigator, since currents coming from the northern into southern seas, will probably be found colder than the water of those seas as the currents from southern seas into northern are apt to be warmer. On his last voyage, in 1785, he made the first attempt in submarine temperatures at moderate depths, using a bottle up to 20 fathoms, and afterwards a cask with valves in each end. Off the Delaware, in 18 fathoms, he discovered that the water at this depth was 58o, which was 12o colder than at the surface.
Although Franklin's chart of the Gulf Stream, published in London, had been rejected by the English shipmasters in 1770, it was certainly adopted by writers on hydrography. The information was given to the public through these works, and the name Gulf Stream came into general use. The importance, too, of gaining all possible information about this mighty river seems to have been realized at this time, and consequently nearly all government vessels were instructed to observe its phenomenon whenever opportunity offered. Among the most prominent investigators was Dr. Charles Blagden, of the Royal Army, while with the British fleet going to and in the American waters in 1776-'77. He observed the temperature in crossing the stream off Cape Fear, and also off the Chesapeake, communicating his results to the Royal Society, in 1781, in a letter urging the essential advantage to be derived by the use of the thermometer. These two, Franklin and Blagden, were the first to demonstrate the usefulness of that instrument, and, since the time of Alaminos, no discovery of like importance had been made which bore so directly on the question of utilizing this great river to the purposes of man's welfare.
Soon after Franklin's and Blagden's discoveries, Mr. Pownall, formerly Governor of Massachusetts, published in 1787 a large chart and a volume of Hydraulic and Nautical Observations on the Currents of the Atlantic Ocean. On this chart the Gulf Stream is laid down closely approximating to that of Franklin's
. He also gives the correct course or tracks which vessels should take; that to Boston "along and beyond the northern edge of the Gulf Stream." To Virginia and Carolina he urged one in about latitude 35o instead of running down to 20o, as was usual.
Franklin on his last voyage was accompanied by a nephew, Col. Jonathan Williams, who was of great assistance in the thermometrical observations and record of results. Such interest was awakened in the mind of Williams that he was led to continue the experiments begun by his uncle. In a memoir read before the American Philosophical Society in 1790 he confirmed Dr. Franklin's account of the temperature of the Stream, and also advanced the theory that banks, shoals, and coasts might be discovered by the use of the thermometer. Williams published a work in 1799 on thermometrical Navigation, containing a chart of the Gulf Stream
and the temperature of the water on adjacent banks. In 1800 a paper was read by Capt. William Strickland on the use of the thermometer in navigation. In his voyages across the Atlantic he had kept daily and sometimes hourly observations of surface temperature, in order to test the theory of Colonel Williams. His investigation was valuable from the discovery of the warm northeasterly extension of the Gulf Stream, for he found in latitude 46o 47' North and longitude 38o 35' west, a temperature of 68o. He says, of this northeast extension, "it probably continues in about a northeast direction entirely across the Atlantic till it ultimately strikes the coasts of Ireland and the Hebrides, after having lost, in its long course in these northern latitudes, much of its heat, and at last being reduced to the temperature of the sea through which it flows." He recommended the employment of vessels to define the limits of this northern branch between latitudes 47o and 60o by the use of the thermometer. Although others before Strickland had noticed floating weeds and American woods in these northern localities, and even Cabot had remarked upon the fact of the beer in the hold of his vessel getting warm, thus surmising a warm current, yet no one seems up to this time to have declared its existence a fact, based upon actual experience and scientific observation.
At the beginning of the nineteenth century, the subject of ocean currents was a favorite one for investigation by the navigator and hydrographer. The thermometer was the accepted instrument in the research, and by the chronometer, which was becoming of greater value and more generally used, the difference between the dead reckoning and the observed positions could be determined with greater accuracy. As we shall see later, from the time of Franklin and Blagden, for more than a century, all the investigation of ocean currents was based solely upon these two instruments, the thermometer and the chronometer, and upon, what in effect is the same as the latter, the drift of bottles, In the year 1802 the first bottle experiments seem to have been inaugurated, the English ship Rainbow throwing overboard several in the NORTH Atlantic, and at intervals these experiments have been continued in all parts of the world up to the present day.
A remarkable thermometrical voyage was made in 1810 by the packet Eliza, from Halifax to England. It was found that in the midst of the warm water of the stream there existed patches of cool water of 10o to 15o lower temperature than the surrounding sea, and having a diameter of over 200 miles. They were thought to have been caused by icebergs and floes which had entered and been melted in the Gulf Stream. In 1811 and 1812, Sir Philip Broke made a great number of observations in the Gulf Stream and described its characteristics. Among other things he states "that beyond the southern boundary of the stream, from the Azores toward Bermuda and the Bahamas, there is a strong set to the southwest or west southwest, that when this countercurrent arrives opposite the outfall of the Florida or Gulf Stream it turns to the southeast along the outer side of the Bahama Archipelago, receiving into its body a large offset of the Gulf Stream which rounds the Matanilla Bank." Another alleged characteristic of the current began to appear in the nautical works of the early part of the century: "That easterly winds press the current toward the American coast, and that the consequences of this pressure are that the breadth of the Stream and its distance from the shore is diminished and it velocity increased, and that in the contrary, winds which blow from the coast produce contrary effects."
Capt. John Hamilton gave to the American Philosophical Society, in 1825, the observations made by him during twenty-six voyages to and from Europe. They consist of temperature of air and water, current of the Gulf Stream for different months, average temperature of the water on soundings off the Delaware, Georges Bank, and on the coast of Ireland. Some of the conclusions arrived at by Captain Hamilton were of great value at the time. He decided that it was impossible to define the limits of the current of the Gulf Stream, owing to the variable influence of the wind; that after it passes the Grand Bank the main Stream proceeds to the southward, while several ramifications, generally not very strong, branch off to the northeast and from that to the east, with countercurrents in the intermediate spaces; that by the frequent use of the thermometer the navigator may always discern where he touches the Gulf Stream, and take advantage of its current or avoid its influence. He further remarks:
I was for a long time almost induced to conclude that some of these currents, particularly those which prevail between the coast of Newfoundland and Europe, were periodically running half the time in one direction and half the time in the other, and the foregoing tables seem to strengthen this conclusion, except the countercurrents near the edge of the stream.
When the current from the northward prevailed to any great extent, a set in the opposite direction near the bank of Newfoundland and on the west coast of Ireland were always observed. The celebrated German, A. von Humboldt, published in 1814 a valuable description of the Gulf Stream, the result of his own observations in crossing it no less than sixteen times, as well as of all the information he could collect from the journals of navigators who had been possessed of the necessary means for exact astronomical observations at sea. He decided that the Gulf Stream was not the same in all seasons of the year, but that its that the Gulf Stream was not the same in all seasons of the year, but that its force and direction depended to a large extent upon changes in the trade winds, and also, that the general torpidity of the ice in the Arctic in the winter and its melting in the summer, influenced it. Regarding the directions of ocean currents he says:
Considering the velocity of the fluid elements which, in different latitudes, in consequences of the earth's rotation, is different, one should be tempted to think that every current from south to north ought to have at the same time a tendency to the east, and, vice versa, a current from north to south a tendency to the west. He published a chart of the Gulf Stream in which he depicted its changeable limits as he believed they were.
During the next few years many navigators cruised in and examined the Gulf Stream, more particularly however in the vicinity of the route between Halifax and Bermuda. One of them in May 1821, in about 64o west longitude remarked the fact that he observed a vein of cool water of a temperature of 54o between 72o and 73o, which seems to be the first time this phenomenon was noticed. The celebrated Englishman, Capt. W. Scoresby, investigated the northern extension of the stream, and discovered in the vicinity of Spitzbergen that an under stratum of water was generally warmer than that at the surface. He believed that the warmer water, though of similar specific gravity was in this case, the most dense, and that sea water followed the same law as fresh water with regard to extreme of density, being a few degrees above its freezing temperature. To this he attributed the fact that the polar ice in these waters could not extend far to the southward, and Humboldt adopted the same. The latter says: "In those regions which are warmed by a current from the southwest, navigation is uninterrupted even in the midst of the strongest winter."
Col. E. Sabine, in 1822 was a member of an expedition organized for the purpose of making experiments to determine the figure of the earth. Sailing from England he went to Madeira and to Sierra Leone, through the Caribbean and the Straits of Florida to New York and thence to England, thus making the complete circuit of the warm Atlantic currents. In his observations on ocean temperatures he found in the eastern Atlantic a body of water very much warmer than normal, and attributed this fact to an unusual elevation of the Gulf of Mexico and the Caribbean, due to abnormally strong trade winds. The weather was so unusual in the southern parts of Great Britain and in France as to have excited general remark, as "most extraordinary hot, damp, stormy, and oppressive," and that in November and December gales from the west and southwest were almost without intermission. We here see, not so much the direct influence of the warm water of the stream on the climate of England and France as the effect of the westerly and southwesterly gales.
During the first quarter of this century the British admiralty office had collected a great quantity of material on the subject of ocean currents and meteorology, most of which had never become known to the public. Mr. James Rennell, who had devoted his life to the subject of geography, and particularly to ocean currents, was given the task of compiling and collecting the data. He combined the results on large charts of the ocean which were the administration of the day, and also wrote a volume on "An investigation of the subject of the currents of the Atlantic Ocean." He died, however, before its entire completion, but two years later (1832) it was published by his daughter Lady Radel. In the charts were embodied the general courses of the currents with the limits of variations, the directions of the winds, accompanied by the date of observation, the depth and temperature of the sea, and some of the tracks of the vessels making specially important scientific observations.
Major Rennell adopted Dr. Franklin's theory as to the principal cause of ocean currents and divided them into two classes: Drift currents, caused by the effect of constant or long-continued winds on the surface of the water, and stream currents, which are formed by the accumulation of water by the drift current meeting an obstacle and thrown sideways or out of its usual course. The Gulf Stream he placed in the latter class, but concluded that it turned south toward the Azores and was lost, while he considered the movement of water in the northern part of the North Atlantic a drift current impelled by the prevailing westerly winds, and these also were the cause of the African current.
From this investigation he pronounced it to be abundantly proved--
(1) That there existed a change in the position and breadth of the column of warm water from time to time.
(2) That the breadth varied at time in the proportion of more than two to one.
(3) That these changes had been observed sometimes to be very sudden--as, for instance, it had once been found to be 140 miles in width, and ten weeks later at the same spot to be 320 miles broad.
(4) That these changes did not follow any regular course of season, for it was 320 miles wide in May, 1820, and only 186 miles in May 1821, nearly at the same place.
(5) That on the northern side of the stream the body of warm water is more permanent than to the south, and also that the warmest water is found to the North, as if indicating the strongest part of the stream there.
(6) That the existence of warm water does not necessarily indicate the presence of the stream, but must be regarded as an overflowing or deposit of superabundant water, or even from a counter current.
(7) That there were without doubt veins of colder water within the body of warm water.
He pointed out the fact, and, indeed, it exists at the present day, that the position of the Stream east of Cape Hatteras is but imperfectly known, and that notwithstanding the great number of observations at his disposal, a want of system in their collection, the isolated and unconnected facts obtained by different observers at different season, and errors in determining longitude made it impossible at that time to state where the borders of the Stream should be placed. The observations discussed by Major Rennell were of the surface temperature, and we shall see later how great is the influence of the wind in spreading the warm water of the Stream without carrying the current with it. His work was the most valuable collection of results that had been made, and while some of his conclusions have since been disproved, it is a remarkable fact that he should have arrived at so near the truth in many of them. An index of his currents is shown here.
For several years after the death of Major Rennell, observation of the Atlantic currents did not possess the attraction that it had previously, probably for the reason that his elaborate compilations were considered to have settled the question. Isolated observations were made, but no one took the trouble to combine them into average results. Rennell's theory of the elevation of the Gulf of Mexico and the Caribbean Sea was much shaken by Arago, who called attention to the observations made to ascertain the difference of level of the two oceans at the Isthmus of Panama.
About this time a line of levels was carried across Florida from St. Mary's River to Apalachee Bay, with a difference of 7 ½ inches, the latter being the highest. It was thought, however, to be due to error of observations rather than to difference of level.
Arago believed "that with respect to currents the rotation of the earth ought principally to be taken into view, and that this together with the cooling and warming of the water in the north and south, is the main cause of their more rapid or slower deviation and progress toward the east or west." He remarks, too, that "we ought to apply to the ocean the same theory which has already afforded a satisfactory explanation to the trade winds if we will decipher the question of currents."
During the first half of the century bottle experiments were numerous. The results were published, chiefly in magazines, in the shape of charts, giving the positions and dates of departure and arrival of these floats, connected by straight lines. Another chart, indirectly relating to ocean currents, was published by Mr. W.C. Redfield. It gave the positions of icebergs and fields observed by British and American navigators in the Atlantic from the year 1832 to 1844. Over one hundred of them were marked on this chart, and the fact observed that they sometimes entered the supposed limits of the Gulf Stream, thus showing the existence of an undercurrent.
In 1838 and 1840 a scientific mission was sent out by the King of France, under the direction of Paul Gaimard, to northwestern Europe. Among other subjects they observed the depth and temperature of the Ocean, and concluded that "a broad current sets through the northern Atlantic in a NNE. direction toward the coasts of Great Britain and, passing between the Faroe and Shetland Islands, runs along the coast of Scandinavia as far as North Cape, from which it turns toward Cherry Islands and Spitzbergen."
The winter of 1845-'46 in England, and in fact in all of western Europe, was very abnormal. The weather was exceptionally mild, being 8 degrees above the average, and was accompanied by much rain and high southwesterly gales, similar to the winter of 1821-'22, when Colonel Sabine had observed an exceptional extension of the warm water of the Gulf Stream toward the shores of Europe. Struck by the similarity of weather, Colonel Sabine endeavored to discover if the same conditions of ocean temperature prevailed, but although hundreds of vessels crossed and recrossed this part of the ocean he could find none on which observations had been taken. He thought it reasonable to believe that through a course of years there might be a difference between the usual and extreme initial velocities, and consequently in some years, as 1776, 1821, and perhaps 1845, it might reach the shores of Europe. He thought, too, that it would be of the greatest practical value for Europe to be informed in advance of the yearly state and tendency of the Stream and the changes in the velocity. His idea was that ships might observe its elevation in the Gulf of Mexico and Straits of Florida, and that they sailing faster than the flow, might make the changes known in England in advance of the arrival of the climate-influencing warm water.
After the death of Major Rennell the first renewed attempt to take up the task of collecting data on ocean meteorology was made by Lieut. M.F. Maury, U.S.N. While he was collecting, however, the U.S. Coast Survey, under Prof. A.D. Bache began, in 1844, a systematic investigation, which continued with greater or lesser regularity until 1860. Before describing the latter, however, we will consider the labors of Lieutenant Maury and others up to the outbreak of the Civil War. Lieutenant Maury, while Superintendent of the U.S. Naval Observatory, had collected all the log-books of vessels between the years 1840 and 1850, and averaging the data, gave to the public the results in a series of wind and current charts and sailing directions. After the first edition was published he proposed a general Maritime Conference for devising a uniform system of observations at sea, and the meeting was held at Brussels in 1853. A plan of observations was adopted and the co-operation of nearly every nation assured. As a result, a mass of data was collected from which other editions of more elaborate charts and sailing directions were compiled. The charts were issued in condensed form by other governments, and his sailing directions, as well as his famous work entitled the "Physical Geography of the Sea," were translated into many languages.
It is stated in some recent works that it is difficult to ascertain from Maury's writings exactly what his ideas were as to the causes of the great ocean currents. He says in "Physical Geography of the Sea:" But they [modern investigations] seem to encourage the opinion that the Stream, as well as all constant currents of the sea, are due mainly to the constant difference produced by temperature and saltiness in the specific gravity of the water in certain parts of the Ocean. Such difference of specific gravity is inconsistent with aqueous equilibrium, and to maintain this equilibrium these great currents are set in motion. The agents which derange equilibrium in the waters of the sea, by altering the specific gravity, reach from the equator to the poles, and in these operations they are as ceaseless as heat and cold, and consequently call for a system of perpetual currents to undo their perpetual work.
These agents, however, are not the sole cause of currents. The winds help to make currents by pressing upon the waves and drifting before them the water of the sea; so do the rains, by raising its level here and there; and so does the atmosphere by pressing with more or less superincumbent force upon different parts of the ocean at the same moment, as indicated by the changes of the barometric column. But when the winds and rains cease and the barometer is stationary, the currents that were the consequence also cease. But the changes of temperature and of saltiness, and the work of other agents which affect specific gravity of sea water and derange its equilibrium are as ceaseless in their operations as the Sun in his course, and in their effects they are endless. Philosophy points to them as the chief cause of the Gulf Stream and of all the constant currents. In another place, however, he says:
The dynamical forces which are expressed by the Gulf Stream may with as much propriety be said to reside in those northern waters as in the West India seas; for on one side we have the Caribbean Sea and Gulf of Mexico, with their waters of brine, and on the other the great Polar basin, the Baltic, and the North Sea, the two latter with waters that are but little more than brackish. This fact would of itself simply neutralize the difference in density due to heat, but later he expresses his conviction that-
If we except the tides and the partial currents of the sea, such as those that may be created by the wind, we may lay it down as a rule that all the currents of the ocean owe their origin to difference of specific gravity between sea water at one place and sea water at another, for wherever there is such a difference, whether it being owing to difference of temperature or to difference of saltiness, etc., it is a difference that disturbs equilibrium and currents are the consequence. His belief was, then, in effect that differences of density caused the main currents, and that this might be modified by winds, rain, barometric pressure, evaporation, and the fauna and flora of the Ocean.
We have now reached the point in the history of the Gulf Stream investigation where, for the first time, can be described a systematic and extensive examination into its secrets. - Research had been going on for years in a casual way, data collected when chance offered, and at any point, but under the direction of no one who had the authority to say to the observers when, where, and how they should search. - The scope of the Coast Survey only contemplated an examination of the Gulf Stream in the portions adjacent to the coast of the United States, but the laws have since been changed so as to include the Sargasso Sea and the Japan Stream, a study of these being considered advantageous to the commercial and scientific interests of this country and the world at large.
In 1842 a report was made by Admiral Sir Francis Beaufort urging the British Admiralty to undertake the work. - The importance of an examination of the great rivers emptying into the Atlantic, to whose influence the Gulf Stream had been attributed, was suggested, and the details of a plan were given for a survey of the Stream from the Gulf of Mexico to the shores of Europe.
This plan proposed the employment of three steamers and one sailing vessel. - One steamer was to remain in the Gulf of Florida for the purpose of keeping a continuous record of temperature and velocity at the point, The sailing vessel was to drift along in the axis of the Stream, while the other two steamers were to operate from the axis to the edges in conjunction with the sailing vessel.
When Prof. A.D. Bache assumed the direction of the Coast Survey, he formulated a complete method of administration and included in it the systematic exploration of the Gulf Stream. - The plan first adopted, based upon the knowledge of the general features of the Stream, was as follows, but it naturally was modified by deductions and inferences from new facts which were brought to light as the Survey progressed:
I. To refer the observations to a medial line or axis, on each side of which it would be more or less in its temperatures, and to run sections perpendicular to this line across the whole width of the Stream.
II. To start from points on the coast whose positions are well known, and to determine by the best means known to nautical astronomy the position of the vessel at frequent intervals, and to check these results if necessary by a return to the coast.
III. To occupy positions at which the temperatures at different depths would be determined, the frequency of which would depend upon the greater or less rapidity of the change of temperature.
As regards seasons for explorations, the summer was regarded as the most favorable for the greater part of the Stream, for the reason that the winter season, at which time the storms and cold rendered observation more difficult, is also the season in which the equilibrium of the currents would be most disturbed by the rapid cooling of the water. - Sounding in winter in stormy weather (with rope) was hardly practicable, and the results obtained were liable to great inaccuracies.
In the spring of 1845 the brig Washington
was commissioned and placed under the command of Lieutenant C.H. Davis, U.S.N., and the following instructions were given him. The first part is quoted almost in full, to show the clearness with which Professor Bache saw the details necessary for such an investigation in order to establish the laws of the Stream in the best manner with the instruments available at that time.
Professor Bache says:
The following questions should be examined:
First. What are the limits of the Gulf Stream on this part of the coast of the United States, at the surface and below the surface?
Second. Are they constant or variable, do they change with the season, with the prevalent and different winds; what is the effect of greater or less quantities of ice in the vicinity?
Third. How may they best be recognized, by the temperature at the surface or below the surface, by soundings, by the character of the bottom, by peculiar forms of vegetable or animal life, by meteorology, by the saltiness of the water?
Fourth. What are the directions and velocities of the currents in this Stream and adjacent to it at the surface, below the surface, and to what variations are they subject? What peculiar arrangements of the currents takes place at the edge of the Stream in passing from the general waters of the ocean into those of the Gulf? Some of these questions will require long-continued observations to solve. If you can obtain something like approximation to the normal condition of the Stream in this summer's work it will be quite satisfactory. Make, then, as many cross sections of the Stream as convenient and as the investigation may show to be necessary. In these sections (1) determine the temperature at the surface and at different depths: (2) the depth of water; (3) the character of the bottom; (4) the direction and velocity of the currents at the surface and at different depths; (5) as far as practicable notice the forms of vegetable and animal life.
Project or note the results as obtained. In the diagram for the temperature at the surface the abscissa will correspond to distance, the ordinates to temperatures, upon a convenient scale arbitrarily assumed. The distance apart at which the observations should be made must depend upon the more or less rapid change of temperature; thus, on the borders of the Stream, they should be more frequent than on either side or within it. The diagrams of the scale of temperature, if made large, will be good guides to the work.
Examine the depth and character of the bottom at the same time. To determine the temperature at a great many depths and at or near the same position, will be difficult and tedious. To avoid the necessity for it, make a complete investigation of the change from the surface to the bottom, at as many points as may appear necessary; thus, for example, make an investigation on the several sections above referred to, on the following lines. Sound before reaching the edge of the stream two lines at or near the edge, two lines within, or as many as appear necessary, two at or near the outer edge and several beyond. As for the lines within the Gulf Stream which are the most interesting, the investigation will show how many will be required. The frequency of the observations in a given depth will be determined by the more or less rapid changes in temperature. Suppose a conjectural diagram to represent the results, the temperature changing rapidly near the surface about a point a, then slowly to a certain depth. A counter cold current being met at b, the change becoming rapid there, this low temperature ranging but slowly toward the bottom at a and b, the observations should be frequent, All the observations on depths and character of the bottom and temperature should be carried quite across the Stream.
It may and probably will turn out that there is a certain depth at which the temperature is invariable for the same position uninfluenced at least by season or by winds, and the assemblage of these points will give a line below the surface constant in direction and velocity, and to determine this will be a valuable practical result.
These sections, with the addition of lines run in the general direction of the Stream, will enable you to represent it on a chart in the usual way, showing the limits and axis, the velocity and direction and temperature at the surface and at any depth which is desirable as that of the line if invariable temperature. As to the character of the bottom, use the Stellwagen Cup and the apparatus which I have requested Lieutenant-Commanding Blake (if he can dispense with it) to send to you at New York. They may both answer the purpose. Characteristic specimens should be preserved, as heretofore, and duly marked with date and position. They will be arranged on your return to the office. The temperature at the surface obtain in the ordinary way or by using the instrument furnished to Commander Gedney last year, and which I shall speak of as the marine thermometer. The velocities and directions of the currents you should ascertain as far as practicable by comparing the positions determined by astronomical observations and by reckoning, by anchoring the vessel or a boat when such a thing is practicable, by the change of position in time of calm. [Observe] The way of the vessel by Massey's Log.
The existence of a counter current of cold water from the poles below the warm current from the equator has been supposed. This current would produce a position of rest, in which if a heavy body attached to a light one at the surface were immersed, the light one would drift off down the stream of the superior current. If a light body were sent down to the counter current and then detached, it would rise at a point up the stream of the surface current. A boat might be anchored on it by attaching to it a body which would produce a considerable resistance to motion. Two boards put together crosswise would answer the purpose well. It may be that if there is no counter current the velocity near the bottom is so much checked as to cause a variation to be discernible in some such way.
The remainder of the instructions is devoted to details of observation.
Lieutenant Davis made two or three trips into the Gulf Stream, and although the means of observation were tentative on this first year's work, much valuable information was obtained. In 1846 Lieutenant George M. Bache, U.S.N., was detailed to continue the Gulf Stream investigation under practically the same instructions as his predecessor. After a summer's successful work in tracing the temperature across the Stream on three sections, the little vessel was overtaken by a hurricane off the North Carolina coast and Lieutenant Bache and ten of the crew were swept overboard by a sea and lost. The vessel managed to reach port almost a wreck, and the observations, made at such a cost in life, were preserved. Lieutenant Bache gave the name "Cold Wall" to the remarkable change in temperature usually found at what is supposed to be the inner edge of the stream, and he also confirmed the fact that there were alternations of hot and cold water across the stream.
In the following year the Washington was commanded by Lieutenant S.P. Lee, U.S.N. His instructions contemplated tracing the axis of the Stream, and testing, on his return from the Gulf of Mexico, the existence of the cold wall south of Cape Hatteras. They also called for a resurvey of the section off Cape Henry in order to connect the series of observations made in different years. The observations made by Lieutenant Lee were in the main a confirmation of those of previous years. He found the alternations of hot and cold water, but their positions did not correspond. Lieutenant Bache found a second branch of the Gulf Stream separated by cold water, while Lieutenant Lee found more than one alternation, and the positions of the highest and lowest temperatures were different in the two years.
In 1848 the work was continued, but with improved means. Two Six's thermometers and two larger on the same plan were used, and also a metallic self-registering thermometer, designed by Mr. Joseph Saxton especially for this work. Instead of a sailing vessel, the U.S. steamer Legare' was commissioned under the command of Lieutenant Richard Bache, U.S.N., and the section off Cape Henry resurveyed and a first examination of the Cape Hatteras section made. The observations of this year furnished data for comparison of the results obtained during three consecutive years on the Cape Henry sections, and were thought to develop the fact that beginning with a minimum at the cold wall, the temperature rises to a maximum in the axis of the Stream, beyond which are two minima and two maxima.
After the observations above mentioned and until 1853, circumstances connected with the work of the Survey prevented the prosecution of Gulf Stream investigation, but in this year a party under Lieutenant T.A.M. Craven, U.S.N., on board the steamer Corwin, was directed to run four sections across the Stream from Cape Canaveral, St. Augustine, St. Simons Sound, and Charleston, and Lieutenant J.N. Maffitt, U.S.N, on board the schooner Crawford, to run the sections from Charleston, Cape Fear, and Cape Hatteras.
In addition to copies of the instructions that had been sent to the former officers engaged in the work, Professor Bache also issued detailed instructions as to the special methods of prosecuting the examinations. The axis of the Stream or the point of highest temperature was to be traced by zigzags, by Lieutenant Craven, from Key West to Charleston, and afterwards as far as the latitude of New York, and, with the exception of the latter, which was unavoidably prevented, all the work laid out was most faithfully executed. The soundings taken by both parties were with rope or by Massey's sounding machine, and from the depths obtained they supposed there were two submarine ridges running parallel to the coast. The soundings since taken with pianoforte wire have proved this to have been an error. The temperature curves obtained this year are of the same form as those previously found farther North, and in the duplication of the Cape Hatteras section it was found that the similarity of curve and the positions of the various warm and cold bands were remarkable.
It was concluded that there were alternations of temperature across the Gulf Stream, the cold water intruding and dividing the warm, making thus alternate streaks or streams of warm and cold water, and it was thought that the observations of Lieutenant Maffitt, on the Charleston and Cape Fear sections, showed a counter current where the cold streaks were found. That such is not always the case will be shown later in discussing the observations of the Blake in recent years. Professor Bache also decided that "the observations of this year have fully proved that in the Charleston section, and those south of it, the bands of cold and warm water are produced by the shape of the bottom of the sea." The progress of the explorations up to 1853 furnished data for the construction of a chart of the Gulf Stream from Cape Canaveral to the section off Sandy Hook, the alternations of temperature being shown by shading, the darker the shade the higher the temperature.
The curves limiting the various bands were not in all cases drawn precisely through the points obtained on the several sections, but in no case but one was the distance from the point actually determined as great as the probable error in the determination of the points themselves. The bands appeared to be invariable in number and position. The supposed axis of the Stream (the highest temperature) was the best determined. The cold wall was the next best to that of the axis, and in the case of the other warm and cold bands the limits of uncertainty in their position at the point of crossing any section were less than half the average distance between the positions in that part of the section.
In 1854 it was thought to be desirable to continue the examination of the St. Simon's and Canaveral sections in winter for a comparison with the summer's work, and Lieutenant Craven was assigned to the duty. The temperatures obtained showed a remarkable dissimilarity of form from those of the summer. The thermometer at most of the positions was nearly constant from 20 to 100 or 120 fathoms, and below that depth it changed rapidly . At Canaveral the double division of the Stream was shown, but the first maximum was about 7 miles nearer the Cape than in 1853, and the second maximum was warmer. What would generally be taken by navigators as Gulf water was 65 miles from the Cape, "but there had evidently been some great disturbance of temperature just before results were obtained."
Later in the year Lieutenant Craven investigated the Nantucket section, running a line SE. by S. from the Davis South Shoal light vessel and making observations at about 20-mile intervals for a distance of 230 miles. He found the warmest water at this distance, which was 40 or 50 miles farther south and east in October, 1854, than it was in August, 1845. The alternations of warm and cold water were discernible, but, as in the case of the warmest, they were a greater distance off shore. In 1855 the work of research was continued, Lieutenant Craven running a section off Cape Florida in May, and Lieutenant Sands along the axis of the Stream in June, and also a section off Nantucket in October. The section off Cape Florida was completed successfully and the axis of the Stream followed as far as Cape Lookout, but in the attempt to finish the Nantucket section only the warm water of the axis was reached. In 1857 a number of interesting observations were added to the Gulf Stream exploration. A section was run from Havana to Sand Key, Florida, the inner edge of the Stream was traced from Cape Canaveral to Cape Fear, the axis was traced from Tortugas to Cape Hatteras, and a line was run from Halifax in the direction of Bermuda. It was unfortunate, however, that the thermometers were not always in working order, as many temperature observations on both the Havana and the Halifax lines had to be discarded. During the next three years the work was chiefly confined to investigating the temperatures across the Straits of Florida.
Although the plan for the exploration of the Stream contemplated the determination of the density of the water and the direction and velocity of the currents, the actual work performed was the determination of temperature and depth. The existence of a polar current underlying and running counter to the Gulf Stream was assumed by Professor Bache, the assumption being founded mainly upon theoretical considerations, and not on actual current observations. Generally the only record of current was obtained by the difference between the dead reckoning and the astronomical positions of the vessels, as, for example, in the record of observations of one party it says:
August 16.--A comparison of the afternoon with the morning sights for chronometer show a current of 5 miles eastwardly. The vessel was lying-to in the interval. The meridian observations showed a northerly current during the last 24 hours.
Another record was:
August 18.--Tried the current with a boat anchored with 1,200 fathoms line (no bottom). Found it on the surface setting SW. by W. 0.29 mile per hour. At 25 fathoms depth, SSW., same velocity. This agrees with chronometer sights of morning and evening, the brig lying-to all day and drifting a little to the west with the sea. The instruments employed in the investigation under Professor Bache were of the most approved patterns, were handled with the greatest care, and every observation scrutinized closely, but the difficulties against which they had to contend rendered the work very laborious and the results sometimes liable to doubt, which necessitated discarding the observation.
The thermometers were as follows: The self-registering instruments of Dr. Rutherford, of Edinburgh, and Six, of Canterbury; a metallic thermometer made by Breguet, of Paris, and another by Mr. Saxton, of the Coast Survey Office. Rutherford's is a minimum thermometer, the cohesion of the spirit drawing an enamel index to the lowest point reached by the contraction where it is left as the fluid expands. To render it applicable to deepsea temperatures it is inclosed in a glass globe made strong enough to withstand moderate pressures. In use it is necessary to keep the tube horizontal, which is not always possible. In using rope, too, for lowering, the centrifugal motion caused by the twisting or untwisting of the rope prevents accuracy or certainty of registration.
Six's thermometer is composed of a bent tube of glass, one of the branches terminating in a large expansion to form a cylindrical chamber and the other only slightly enlarged at the end. The lower part of the tube contains mercury, which partly fills both branches on either side of the bend. The upper part of each branch including the chambers, is filled with highly rectified spirits of wine. A rise or fall of temperature will cause a greater expansion or contraction of the spirits in the larger end than in the smaller, which will cause the column of mercury in that branch to rise and fall, and thus a motion is communicated to its surface in both branches. A small index of steel, coated with glass and lightly held in place by a delicate spring, is pushed along by the surface of the mercury and remains at the farthest position where the mercury withdraws.
The Breguet metallic thermometer is constructed on the principle of the unequal expansion of metals. The compound bar is composed of laminae of brass and steel united together and bent into horseshoe form. One end is firmly fixed and the other, being free to move under the influence of the unequal expansion or concentration of the two metals, gives rotary motion to an index and registers on a dial by means of an auxiliary hand held by friction at the highest or lowest point of temperature. The hole is inclosed in a brass case made sufficiently strong to withstand pressure.
Saxton's thermometer is the same as the Breguet in principle, but the laminae are composed of silver and platinum and wound in a spiral instead of being bent into horseshoe form. It is heavily gilded and inclosed in a metal case, into which the sea water is admitted. According to our ideas at the present day these instruments were faulty.
The conclusions adopted by Professor Bache from the observations taken under his direction between 1854 and 1860 were as follows: That between Cape Florida and New York the Gulf Stream is divided into several bands of higher and lower temperatures of which the axis is the warmest, the temperature falling rapidly inshore and more slowly outside. This is not only the case at the surface, but, with modifications was easily understood, at considerable depths. That between the coast and the stream there is a fall in temperature so abrupt that it has been aptly called the "Cold wall." The cold wall extends, with varying dimensions and changes of its peculiar features, along the coast from Cape Florida northward as far as examined. Inside this wall of marked colder temperature there is another increase, while outside the warmest band, which is next the cold wall, there is another warm and one other cold band. The distance these are situated from the coast are shown in the following table: (image not available)
In the sections on which the work was duplicated, viz, the Cape Henry and the Cape Hatteras sections, the positions of the cold wall and axis of the Stream agreed within 51/2 miles, and those of the succeeding points of maximum and minimum temperature within 71/2 miles.
After the year 1860 Gulf Stream investigation ceased almost entirely until 1867, when Prof. Henry Mitchell of the Coast Survey sounded between Key West and Havana and observed the currents to the depth of 600 fathoms, the deepest ever attempted to that date. The method adopted to observe these currents was the following: Two globes or cans of equal surface were attached to each other by a line of the desired length. One of the globes was loaded so as to sink to the length of the connecting line, while the other was on the surface supporting its mate. Within the latter was a light reel upon which a small log line, passing through an aperture, was wound by a crank from without. To the end of the line was secured a third globe floating freely upon the surface of the water. When making an observation the log line was reeled until the surface globes were together. At a signal the reel was released, and, if the currents influencing the two were different, the amount of separation in a given time indicated the relative velocities.
A trail was made of surface currents and at 300 and 400 fathoms depth, at a station 3.7 miles from Fort Chorrera, Cuba, and a velocity of about one knot was found at each. Another trial was made about 3 miles farther off shore, with the result, that at 600 fathoms depth the current was about 10 per cent less than on the surface. From these experiments, Professor Mitchell was led to conclude that "the Gulf Stream has a nearly uniform velocity and constant course for a depth of 600 fathoms, although its temperature varies in this depth 40oF." In the following year Professor Mitchell continued current observations in the Santaren and St Nicholas Channels, using an anchored buoy for the initial point from which to start the float for service observations. His conclusion was that the water in these channels was motionless.
In 1868-'69-'70 expeditions were fitted out by the British Admiralty, and, under the scientific direction of Dr. William B. Carpenter, Mr. J. Gwyn Jeffreys and Prof C. Wyville Thomson, sounded and dredged off the coast of Europe from the Faroe Islands to Gibraltar. Accurate temperature observations were taken, and from these Professor Thomson has given the course of the currents in what is called the northeastern extension of the Gulf Stream. By the term Gulf Stream he explains:
I mean that mass of heated water which pours from the Straits of Florida across the North Atlantic and like wise a wider but less defined warm current, evidently forming part of the same great movement of water, which curves northward, to the eastward of the West Indian Islands. I am myself inclined, without hesitations, to regard this stream as simply the reflux of the equatorial current, added to, no doubt, during its northeasterly course by the surface drift of the anti-trades which follow in the main in the same direction.
Of the course of the Gulf Stream he says: "It seems to me that the Gulf Stream is the one natural phenomenon on the surface of the earth whose origin and principal cause, the drift of the trade winds, can be most clearly and easily traced." He concludes that the Stream enters the North Atlantic and accumulates. Finding no free passage toward the northeast, a portion of it goes toward the Azores, but the accumulation to the northward forces a return eddy current to underrun certain portions of the warmer flow.
In 1873, the Challenger expedition, under the command of Captain Sir George Nares, R.N., with a full staff of scientific gentlemen, of which Professor C. Wyville Thomson was the head, added some most valuable data to the record of Gulf Stream investigation. They crossed the North Atlantic twice, and made passages north and south along the shores of both hemispheres, making the most accurate observations of temperature and specific gravity. In the passage of the Challenger across the Gulf Stream off New York, and between Halifax and Bermuda, the alternations of warm and cold water were found. They also at times made observations of the strength and direction of the currents, both surface and subsurface, using practically the same method as that employed by Professor Mitchell in the Straits of Florida in 1867.
The Coast Survey continued its examination in the Gulf Stream in sounding and dredging during the years 1868 to 1878, with the steamers Bibb, under Acting Master Robert Platt, U.S.N., the Bache,
under Commander J.A. Howell, U.S.N., and the Blake,
under Lieutenant Commander C.D. Sigsbee, U.S.N. Mr. L.F. Pourtales and Professor Louis Agassiz accompanied the vessels at different times for the purpose of collecting and arranging the results of the dredging operations. In 1879 the investigation was extended into the Caribbean, and a theory advanced as to the flow of its waters by Commander John R. Bartlett, U.S.N. who commanded the vessel.
In his report accompanying the record of the season's work he concludes that the equatorial current, which sets directly against the Windward Islands, is by them and their connecting ridges deflected northward, and so following their outer edge passes around the Virgin Islands to the westward and through the deep channel to the northward of San Domingo. He suggests, also that on reaching Cuba the current divides, a part flowing northwest through the old Bahama Channel and a part through the Windward passage between Cuba and San Domingo, and thus by Cape San Antonio into the Gulf of Mexico. His report states that the specimens of bottom taken in the Windward passage give evidence that the current moves in depths greater than 800 fathoms and that it reaches the bottom. He remarked, too: "The current, always found flowing north along the eastern side of South America, on reaching the island of Tobago divides, part joining the equatorial current setting north along the chain of Islands, the remainder following the coast line of Trinidad and the Spanish Main, and so around the entire circumference of the Caribbean Sea, finding at last an outlet at the Mona Passage and the Anegada Channel to join the equatorial current on its way to the Gulf of Mexico." This circulation is so contrary to that found in the later investigation made by the Blake that it is given in full. Professor Alexander Agassiz accompanied Commander Bartlett on this cruise, and while he quotes that latter on this subject he does not seem to adopt these ideas without question, for he says: "In the present state of our knowledge it is difficult to trace the path of the equatorial water as it is forced into the eastern Caribbean."
In 1877 the first attempt was made by the U.S. Coast Survey to systematically observe ocean currents from a vessel anchored at sea. The schooner Drift was built for this purpose, and under command of Acting Master Robert Platt, U.S.N., successfully observed the currents between Nantucket and Nova Scotia, occupying eight stations for varying periods, the longest time being over 90 hours and the greatest depth of water 135 fathoms.
The first reliable soundings which developed the bed of the Gulf Stream from the Straits of Florida to George's Bank were made by Commander Bartlett in 1881 and 1882. It will be remembered that the soundings by Lieutenants Davis, Lee, Craven, and others before 1860 were made with rope or registering devices, such as Massey's, and when these are used in a strong current or in considerable depths they are unreliable. Commander Howell, when in command of the Coast Survey steamer Bache, was provided with one of the Thomson wire sounding-machines, which had been so successfully used by Captain Belknap on board the U.S.S. Tuscarora in the Pacific. The principle of sounding with piano-forte wire was much improved by his successor, Lieutenant-Commander Sigsbee, so that any depth could be ascertained with certainty and accuracy in almost any weather, and since that time the Blake has used nothing else for the purpose.
Commander Bartlett ran lines about normal to the coast at intervals of 60 miles from Jupiter Inlet North. He says:
Instead of a deep channel which had previously been reported, our soundings show an extensive and nearly level plateau extending from a point to the eastward of the Bahama Banks to Cape Hatteras. Off Cape Canaveral it is nearly 200 miles wide, and gradually decreases in width to the northward until reaching Hatteras, where a depth of more than 1,000 fathoms is found 30 miles off the shore. This plateau has a general depth of 400 fathoms, suddenly dropping on its eastern edge to 2,000 fathoms. The soundings in the strength of the current were all taken with a 60-pound shot, the time allowed for the sinker to reach the bottom being less than one minute to each 100 fathoms in depth.
In the lines crossing the Stream from Nantucket to Bermuda and returning to Cape Hatteras, Commander Bartlett took serial temperatures at short intervals and surface observations every mile. He says:
In regard to the results of the investigation of this last season's work, I have been particularly interested in what I was expected to find--that is, the bifurcation of the stream into warm and cold bands. The warm and cold bands have been accepted for so long a time as a fact and have been reported by such reliable authorities that there must have been conditions of weather during our observations. I have already stated that our observations did not indicate anything of the kind.
In 1883 Lieutenant J.C. Fremont, Jr., U.S.N., in command of the schooner Drift, was detailed for the first Gulf Stream current investigation to be made from a vessel at anchor. The vessel was supplied with 700 fathoms of galvanized wire rope three-quarters of an inch in diameter, and instructions issued to observe current at various places near the 100 fathom curve along the Coast, and also in the stream between Jupiter Inlet and Memory Rock. The Drift is a small deep-draft schooner of about 100 tons. Not being fitted with a steam windlass, the rope, which was coiled on deck, was veered and hove in by hand. In spite of this, Lieutenant Fremont succeeded in occupying five stations across the channel, the deepest anchorage being over 400 fathoms. The currents were observed by floating cans attached to a log line. It was discovered that, "contrary to expectation, the greatest velocity was not found at the supposed center of the stream, but somewhat to the westward of it. The greatest velocity noted was 4.7 knots in latitude 27o05' north and longitude 79o44' west. The depth here was only 190 fathoms, the distance west from the supposed axis 10 miles, and from the Florida coast about 20 miles."
Before beginning the description of the Blake's examination of the Gulf Stream under my command there is one other investigation to which allusion should be made. His Highness the Prince of Monaco during the past years has been engaged in scientific researches on the coast of France. The object of his examination was primarily for the purpose of discovering the cause of the departure of the sardines from the Bay of Biscay; but in connection with this he has devoted much of his time to a study of the eastern portion of the Gulf Stream. In order to discover the velocity and direction of this current he adopted the method of floats, but carried it out in a manner and magnitude never before attempted. His floats were barrels and bottles to a limited number, but mostly were specially constructed copper globes, and all were ballasted so as to expose as little surface as possible to the wind and waves. The ballast of the barrels and globes was suspended several feet below the surface of the water, and so arranged that by the time the float accumulated a quantity of material (barnacles, grass, etc.) the ballast would become detached.
He put overboard from his yacht no less than one thousand six hundred and seventy-five of these floats. In 1885, one hundred and thirty-nine in a distance 170 miles northwest of Azores. In 1886, over five hundred more were placed along the twentieth meridian off the coast of France. In 1887, nine hundred and thirty-one were set adrift between the Azores and Newfoundland, and afterwards another line farther to the northward and eastward in the region of the supposed northeast extension of the stream near the fiftieth parallel. Dividing each of the lines into thirds for purposes of study, he found that most of the floats traveling to the southward came from the southward and middle groups, and of those going to the northward and eastward most of them belonged to the northern groups, but there were some from each group which had traveled in the opposite directions. Of those placed between the Azores and Newfoundland, one from near the northern end of the line and one from near the middle were found in Ireland, others from near the same points traveled to the coast of Norway, and more were distributed along the shores of France, Spain, and Africa. None of those started near the Azores were found north of Lisbon. Two of those from the northern end of the line off the coast of France found their way to the West Indies.