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CHAPTER III.
GULF STREAM INVESTIGATIONS MADE BY THE U.S. COAST SURVEY
UNTIL 1884 AND THOSE CONTEMPORARY WITH THEM
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.
(See
illustration No. 37.)
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.
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