THE CHALLENGER 
355 
to the surface the index on the maximum side had not 
moved, while that on the minimum side showed in every 
case the temperature at the deepest point to which it had 
been sunk, the temperature falling as the depth increased. 
But now on account of the enormous masses of ice be- 
neath the surface the coldest layer of water was not at 
the bottom, and the thermometers from all depths below 
the zone of lowest temperature showed merely the tem- 
perature of that zone and gave no information as to what 
the condition of things might be beneath it. After some 
experimenting it was found possible, by cooling the ther- 
mometers down to the temperature of melting sea-ice 
before setting the indexes, to utilise the maximum side 
for reading the temperature below the cold zone and 
thus it was ascertained that in the depths of the Antarctic 
Sea there were layers of water of higher and lower 
temperature sandwiched one above another. Since the 
Outer Case of Miller- Casella 
Deep- Sea T h er m o m eter. 
cruise of the Challenger deep-sea thermometers on an 
entirely different principle have been perfected, making 
it possible to ascertain the exact temperature at any 
point of depth. 
The interest of these observations does not lie in the 
gratification of an idle curiosity as to how warm or cold 
