Fig. 4. Section of Assmanris Aspiration Fsychromeier . 
20 
HINTS TO TRAVELLERS. 
Dr i'm Wet. 
and the clockwork wound up. Air will then he 
drawn over the bulbs for five minutes or more, 
and if the temperature of each thermometer 
has not become steady by the time the clock¬ 
work has run down, it must be wound up 
again. 
The thermometers in Assmann’s Psy chrome ter 
are graduated according to the Centigrade scale, 
and each degree is subdivided into fifths on a 
slip of porcelain enclosed in the outer tube of the 
thermometer (see p. 13). 
Minimum Thermometer .—The minimum tem¬ 
perature of the night can usually be ascertained 
by a traveller exposing a minimum thermometer 
when the camp is set up and reading it in the 
morning before starting on his way. There are 
several forms of minimum thermometer, but 
the only one likely to be used is that known 
as Rutherford’s. It is very delicate and liable 
to go out of order. The instrument should be 
of full size, as used in meteorological stations 
at home ; it must be packed so as to be as free 
as possible from shock or vibration, and ought 
to be carried in a horizontal position. The bulb 
is filled with alcohol or some similar clear fluid, 
and within the column of spirit in the stem 
there is included a little piece of dark glass 
shaped like a double-headed pin. This is the 
index which continues pointing to the lowest 
temperature until the instrument is disturbed 
or re-set. The thermometer has to be hung in 
a horizontal position. When the temperature 
rises, the column of spirit moves along the tube, 
flowing past the index without disturbing it. 
When the temperature falls, the spirit returns 
towards the bulb, flowing past the index until 
the end of the column touches the end of the 
