EQUIPMENT. 



19 



instrument were precisely the same as those of the Miller-Casella 

 thermometers for the siu-face and the maximum depth ; but for 

 intermediate positions, it was observed that the electrical ther- 

 mometer in almost every case gave a slightly higher reading. 

 This discrepancy may be accounted for, Sir William Siemens 

 thinks, by the fact that the electrical thermometer gives the 



Fig. 15. — C. 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 



