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 Hues 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. The schooner Qrampna 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 becaiise 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 investigationg. 



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 current 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 efi"ect upon these waters, 

 and the final position reached after a cycle is completed will dex)end on the relative 

 velocities of the winds. It is 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 it is 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 

 F. R. 93 3 



