CHEMICAL AND PHYSICAL NOTES. 143 
Thus we should have— 
Excess temperature, divisions . 4°8 2:4 1:2 0°6 O73 0°15 0-075 
Time elapsed, seconds . 0 20 40 60 80 100 120 
In this imaginary case the temperature of the thermometer will 
have attained that of the water in 120 seconds, or two minutes. 
When the water touching the thermometer is moving, whether 
the water runs past the thermometer or the thermometer runs 
through the water, then the time which the thermometer requires to 
lose its excessive heat is very much shorter. In actual sounding 
practice the thermometer arrives at the depth at which it is to 
register the temperature, having already very nearly the temperature 
of the water at that depth. It is, therefore, generally speaking, quite 
safe to despatch the messenger, which is to overturn the thermometer, 
so that it may arrive at the required depth not later than one or 
two minutes after the thermometer. This refers only to oceanic 
work. The physicist must himself test the actual thermometers 
which he has on board by vbserving them in still water and when 
moved at certain velocities in water, and from his own observations 
he will form his own opinion of how long the particular instruments 
with which he is supplied have to be left down, and then he will use 
his knowledge to guide his practice. 
Application of Calorimetry to Hydraulics—An interesting ex- 
ample of the application of calorimetry to problems of physical 
geography is afforded by some hydraulic experiments made by the 
writer in the Engadine in the summer of 1894. About a mile 
below the end of the Morteratsch glacier, the muddy stream which 
proceeds from the glacier is joined by the perfectly clear waters 
of the stream which descends from the summit of the Bernina 
pass, the waters of which drive the machinery for the supply 
of electricity to Pontresina. In the afternoon the glacier stream is 
running strongly, and its temperature was found to be 1°C. The 
temperature of the water of the Bernina stream was 11°C. Two or 
three hundred yards below the confluence, where the waters had 
been well mixed, the temperature of the water was 2°5°C. If we 
represent by M the flow of the Morteratsch and by B that of the 
Bernina stream, we have the reiation M:B::10:1°5, whence we 
have B = 0°15 M, or the stream below contains 85 per cent. of 
Morteratsch water and 15 per cent. of Bernina water. 
Temperature of Insolation.—In a meteorological outfit it is usual 
to include a thermometer with blackened bulb enclosed in an ex- 
ternal glass tube. ‘This is to be exposed to the direct rays of the sun 
until it rises to a temperature which remains stationary. This tem- 
