CHAP. VII. ] DEEP-SHEA TEMPERATURES. 993 
ment.’ A modification of Phillips’s maximum ther- 
mometer devised by Sir William Thomson, in which 
the thermometer is entirely encased in an outer 
shell of glass partly filled with alcohol, appears to 
have the smallest error of all. 
A neat modification of Breguet’s metallic ther- 
mometer was designed by Joseph Saxton, Lsq., of 
the U.S. Office of Weights and Measures, for the 
uses or the U.S: Coast © Survey: <A) riband=-of 
platinum and one of silver are soldered with silver 
solder to an intermediate plate of gold, and the 
compound riband is coiled round a central axis of 
brass, with the silver within. Silver is the most 
expansible of the metals under the influence of 
heat, and platinum nearly the least. Gold holds an 
intermediate place, and its intervention between the 
platinum and silver moderates the strain, and pre- 
vents the coil from cracking. The lower end of 
the coil is fixed to the brazen axis, while the upper 
1 In Messrs. Negretti and Zambra’s list of meteorological instruments 
published in 1864, a deep-sea thermometer on this plan is mentioned 
(p. 90): ‘The thermometers constructed for this purpose do not differ 
materially from those usually made under the denomination of Six’s 
thermometers, except in the following most important particulars :— 
The usual Six’s thermometers have a central reservoir or cylinder 
containing alcohol; this reservoir, which is the only portion of the 
instrument likely to be affected by pressure, has been, in Negretti and 
Zambra’s new instrument, superseded by a strong outer cylinder of 
glass, containing mercury and rarefied air. by this means the portion 
of the instrument susceptible of compression has been so strengthened, 
that no amount of pressure can possibly make the instrument vary.” 
Some obscurity is introduced into this passage by the use of the word 
‘superseded ;’ but I am assured by Messrs. Negretti and Zambra that 
in principle this instrument was exactly the same as that devised by 
Professor Miller and constructed by Mr. Casella. 
