292 



THE DEPTHS OF THE SEA. 



[CHAP. vii. 



and I have always regarded it as a remarkable 

 evidence of my friend's care and skill that he 

 landed those two precious instruments at the end 

 of the year safe back at Woolwich. 



Fig. 53 represents the latest im- 

 provements on the Miller- Casella 

 modification of Six's self-registering 

 thermometer. The instrument is of 

 small size, to reduce as far as pos- 

 sible the friction in passing through 

 the water. The tube is mounted in 

 ebonite, to avoid the expansion of a 

 wooden mounting in the water, by 

 which the instrument is liable to 

 get jammed in the case. The scale 

 is of white porcelain, graduated to 

 Fahrenheit degrees; the large bulb 

 is enclosed in an outer shell three- 

 fourths filled with alcohol and her- 

 metically sealed. It is right to 

 mention that I am informed by 

 Sir Edward Sabine that the ther- 

 F 'protectii?g 0pp the ^Miiier- mometers used by Sir John Ross 



Casellathermometer. The ... . 



ends of the case above and m JQS Al'CtlC VOVa^e 1U 1818 WCr6 



below are perforated to J O 



^water protected somewhat on the same 



principle, and that a thermometer 

 for resisting pressure was constructed under the 

 directions of the late Admiral Fitzroy, at the 

 suggestion of Mr. Glaisher, which differed from 

 the Miller-Casella pattern in little else than the 

 outer shell being partially filled with mercury 

 instead of alcohol, and in being somewhat less 

 compact and more fragile than the latter instru- 



