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the gulf stream by john elliot pillsbury

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CHAPTER II

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 (Illustration No. 33).

Franklin's theory on the subject of the cause of the Gulf Stream is givn in the same report. He says:

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. He says:
 
  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 (Illustration No. 34). 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 (Illustration No. 35) 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 in illustration No 36.  

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. Triangulation was carried from Chagres to Panama, and a report made that the Atlantic might be from 3 to 5 feet lower than the Pacific.*  

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.

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