REPORT OF COMMISSIONER OF FISH AND FISHERIES. 33 
As the steamer Blake could not be spared for this purpose in 1891, the parties upon 
the schooner Grampus and the Nantucket New South Shoal light-ship were the only 
ones in the field. As it was considered inadvisable to make a regular series of 
observations over the entire area this year, such lines were chosen as would serve to 
bring out the essential character of conditions supposed to exist. Each line run, 
however, was equivalent to one that had been utilized in previous years, but the 
distance between the lines was greater. Theschooner Grampus occupied 148 stations 
along 13 such lines, making a total of about 1,500 serial temperature observations of 
the water and over 300 determinations of its specific gravity. In the same connec- 
tion over 11,000 hourly meteorological observations were recorded. The light-ship 
party was on duty from July 3 to August 17, during which time it made 500 serial 
temperature and 250 specific-gravity observations of the water, besides a special 
series of over 1,000 hourly determinations of specific gravity. The hourly observa- 
tions respecting meteorological conditions by this party amounted to 17,000. The 
total number of observations made in 1891 was, therefore, 32,000, as compared with 
39,000 the previous year, when three parties were at work. 
The relations of the Gulf Stream to the Labrador current, as brought out by this 
study, are especially interesting because of their bearing upon the migrations of 
schools of fishes. The region off the southern coast of New England was chosen for 
this inquiry because it was supposed that the contrasts between the currents would 
be more distinctly shown there from the fact of their being forced closer together by 
the projection of the mainland to the southeastward from its general curve. This 
expectation was realized in the course of our investigations. 
The 50° curve of temperature obtained by plotting the observations made at the 
different stations has been an interesting one from the beginning. It has been 
the means of demonstrating the fact that there are two sets of conditions under 
which these two distinct bodies of water come into contact. It will be convenient 
to speak of these two portions of the main cufrent of the Gulf Stream separately 
under two headings, namely, the upper portion and the lower portion, 
Upper portion.—The boundary between the cold and warm waters at the surface is 
very seldom a straight line, perpendicular to the surface of the water. It marks 
the position of the resultant of all the forces at work. Of course the general posi- 
tion of the boundary will be determined by the velocities of the two bodies of water 
and their direction when they come in contact. If we leave out of consideration, 
for the present, the wind as an effective agent in the production and directing of the 
ocean currents, we find that in addition it becomes a most potent factor in the 
causation of the changes which are produced in the position of the boundary line at 
the surface. The winds certainly sway the surface waters of these currents one way 
or another; it may be for miles in one direction or the other; just as they may retard 
or reenforce them in their general direction. 
The winds which blow over this portion of the North Atlantic may, for conven- 
ience, be divided into two classes. One may be said to blow in a southeasterly 
direction and the other in a northwesterly direction. The general tendency of the 
first group or summer set will be to drive the warmer waters at the surface toward 
the coast, thus forcing them above the colder waters of the Labrador current. The 
other or winter set may be considered to have the opposite effect upon these waters, 
and the final position reached after a cycle is completed will depend on the relative 
velocities of the winds. Itis not denied that there are other factors which enter 
into this result, or that this position is not affected by the physical characters of the 
| waters, viz, their relative temperatures, densities, etc., but itis claimed that, after due 
allowance is made for these other factors, the winds are the most active causes of 
the daily and seasonal variations which take place in the position of this boundary. 
While these motions may equalize one another and the resultant position remain 
the same from year to year, it is supposable that there may be an excess in one or 
the other of these directions for a series of years, with the result that the boundary 
RR. 93——3 
