20 THREE CRUISES OF THE “BLAKE.” 
the water surrounding it, and a second period of five minutes 
for adjusting the temperature of the comparison-coil on deck. 
Allowing five minutes more for lowering the cable, fifteen min- 
utes sufficed to complete a deep-sea observation. 
The instrument was sufficiently tested by Commander Bart- 
lett, during the season of 1881, to show its entire practicability. 
The accompanying table is taken from his Report to Pro- 
fessor J. E. Hilgard, the superintendent of the United States 
Coast Survey : — 
Depth in Fathoms. Siemens. МіШег-СавеПа. 
Бие B CS wur T ee NET УЛ cx eee 77} 
oy fais: Rove шик c LE иеме I P 754 
IE e уш acis D 69 
1| 4 у eg er Se | er 
20 e Pc qu M o, NUUS › TN 0р 57 
30 Ce Nr cus с C APER VE bore 51} 
BES ОЧ a a. CDL 524 
eo v. 4 ees ke 531 
38 wi UM. du EUN. у uh EE 49} 
S а INR S NM n 
150 LEM oup Pu MEE M BO 46 
200 dcl qe M c gid a ne M ae 43} 
300 (e E E or мы EDU UL Ca caer ТЫ ШО 40$ 
aog e T адан a NUM 393 
te eS э. ел1. . ил те 39 
600 uv OT p NEW UN VEU MN ва Аа 384 
PLE T лл Mae A ici о д8 384 
Ел л, ома cue DN 38} 
Much yet remains to be done before we can ascertain accu- 
rately not only the force, but also the direction of the currents, 
at different depths, from the surface to the bottom ; the floats 
usually employed to make these observations are rather primi- 
tive instruments. Here also we must look to electricity for the 
means of making simultancous or continuous observations. 
The specific gravity of the sea-water was determined on the 
* Blake ” by means of an apparatus devised by Professor J. E. 
Hilgard (Fig. 16) of the Coast Survey. As the differences of 
density are very small, the instrument must be one of great 
delicacy ; it is constructed upon the same principle as that of 
1 According to Commander Bartlett, 30 fathoms, which was not detected by 
the Siemens apparatus recorded the the Miller-Casella, indicating only max- 
presence of a warm belt between 10 and ima and minima. 
