CHAP. VII. J 



DEEP-SEA TEMPERATURES. 



295 



depths in the ocean, to determine the amount and 

 sources of error, to ascertain which was the most 

 satisfactory instrument, and if possible to construct 

 a scale by which the observations hitherto taken 

 with ordinary instruments might be roughly cor- 

 rected, so as to be made available. As there was 

 some difficulty in getting the use of a suitable press, 

 Mr. Casella undertook to have a testing apparatus 

 constructed at his own place in Hatton Garden, 

 capable of producing a pressure of three tons on 

 the square inch. 



The results were very interesting. 1 The first expe- 

 riment went to test the value of the various instru- 

 ments. A Miller- Casella thermometer was placed in 

 the cylinder with No. 57, a good thermometer by 

 Casella, of the ordinary Hydrographic Office pattern, 

 and they were subjected together to a pressure of 

 4,032 Ibs., equal to 1,480 fathoms, with the following 

 result : 



That is to say, the temperature remaining the same, 

 the pressure forced up No. 57 to 12'75 C., and left its 

 index there. 



1 On Deep Sea Thermometers, by Captain J. E. Davis, R.N. Nature, 

 vol. iii. p. 124. Abridged from a Paper read before the Meteorolo- 

 gical Society, April 19th, 1871. 



