CHAP. VII. ] DEEP-SEA TEMPERATURES. 995 
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.’ 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 lbs., equal to 1,480 fathoms, with the following 
result :— 
Difference of 
Thermometer. ss nes ae -: 
Maximum. 
| | 
Minimum. Maximum. | 
| 
| 
Before. 
| | 
— 
| 
| 
After. Before. After, 
| 9 | 8 6C. | 8 6C. | 8 6G. |.8: 85C| 0° 25.¢. 
| Seer wise. Wercr | 4 15 
| | | 
That is to say, the temperature remaining the same, 
the pressure forced up No. 57 to 12°-75C., 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. 
