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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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