EQUIPMENT. 19 
instrument were precisely the same as those of the Miller-Casella 
thermometers for the surface and the maximum depth ; but for 
intermediate positions, i& was observed that the electrical ther- 
mometer in almost every case gave a slightly higher reading. 
This diserepaney may be aecounted for, Sir William Siemens 
thinks, by the fact that the electrical thermometer gives the 
BATTERY. = 
|, =Гє] 
Fig. 15. — С. W. Siemens’s Deep-Sea Thermometer. (Bartlett, U. S. Coast Survey.) 
temperature of the water actually surrounding the coil at the 
moment of observation, whereas the Miller-Casella instrument 
brings to the surface, or at least its readings are affected by, 
the maximum or minimum temperatures encountered in its as- 
cent or descent, which may not coincide with that at the point 
of stoppage. This furnishes a very strong argument in favor 
of the superior accuracy of the electrical instrument. (Fig. 15.) 
It was found that about five minutes. must be allowed at each 
observation for the resistance-coil to assume the temperature of 
