REPORT OF COMMISSIONER OF FISH AND FISHERIES. LXXIX 
the expense of maintaining a sufficient number to afford appreciable 
results. Recourse must be had to other means for obtaining that infor- 
mation. The Fish Commission vessels are all provided with thermome- 
ters and density apparatus of the most approved patterns, but hitherto 
these have beeu regarded rather as accessories to the dredging and 
fishing out fit, and the temperature and specific-gravity observations have 
been supplemental to the collecting work . Consequently these observa- 
tions have not been carried on systematically, either at fixed stations or 
along definite lines, and the records are of little value for determining 
the temperature and density variations in any special region. Until this 
subject has been studied in a thoroughly comprehensive way, we can 
not expect to make any advancement toward the explanation of those 
mysterious laws which govern the arrival and departure of pelagic 
fishes. Observations taken at the surface and bottom only are inade- 
quate for the purpose. They must be carried through successive 
depths of water, being most numerous at those levels where the varia- 
tions are most pronounced and the changes most frequent. 
The investigations made by the steamer Albatross , between 1883 
and 1887, have furnished the clearest insight into the physical char- 
acteristics of the waters off the Atlantic coast of the United States, 
especially south of Xew England and Long Island, where the greatest 
amount of work was done, and yet her observations are altogether 
incomplete for the purposes set forth above. The superficial relations 
of the Arctic current, flowing southward along the coast, and the Gulf 
Stream, flowing northward on the outer side, are generally understood. 
The serial temperatures taken by the Albatross show, however, that 
the transition from warm to cold water is not uniform at all depths 
and at all times, the Arctic current tending to indent the Gulf Stream 
on its inner face, producing in the same section very unequal bands of 
temperature, and indicating superimposed currents flowing in opposite 
directions. Another feature demonstrated by the Albatross was, that 
the border of the continental platform where the slope begins is partly 
bathed by the warmer waters pertaining to the Gulf Stream belt. Thus 
a somewhat tropical fauna is carried far northward, occupying a rather 
narrow zone between the cold water covering the inner surface of the 
platform and that which characterizes the deeper portions of the ad- 
jacent ocean. Here also was the habitat of the tilefish ( Lopholatilns 
chamceleonticeps ), whose sudden extermination in the spring of 1882 
gave additional proof that the conditions which prevail in this region 
are unstable and fluctuating. The facts are insufficient to explain 
those conditions, but they indicate an interesting and perplexing prob- 
lem in the solution of which important practical results may be antici- 
pated. The principal pelagic fishes make their appearance from the 
direction of the Gulf Stream, moving inshore and northward as the 
season advances. With what hydro-isotherm is the approach of each 
species coincident, and do the movements of those isotherms correspond 
