50 
CRUISE OF EM.S. CHALLENGER. 
The thermometers (Fig. 7) used to ascertain the 
temperature at the bottom or at any intermediate 
depot are self-adjusting maximum and minimum 
instruments, known as Miller-Casella thermometers, 
from the names of their inventor and maker, and 
Fig. 7. 
Thermometer Outer Casing 
are so constructed as to resist the pressure of the 
water at very considerable depths. They consist of 
a curved tube with a bulb at each end, one of 
which is filled with creosote, the expansion and 
contraction of which gives the temperature. The 
