HYPSOMETRXCAL APPARATUS. 
13 
a brass tube, C, that supports the boiler, D; and 
a telescopic tube, E, which fits tightly on to the 
top of the boiler. The thermometer is passed 
down the tube, E, from the top until within a 
short distance from the water, which it should 
never touch , and is supported in that position 
by an india-rubber washer, F. The steam passes 
from the boiler up the tube, E, and escapes by 
the hole, G. To pack this instrument for tra¬ 
velling, withdraw the thermometer, and put it 
into a brass tube, lined with india-rubber, having 
a pad of cotton-wool at each end; take off the 
tube, E, shut it up, and put the small end into 
the boiler, D, which it fits, then withdraw the 
spirit lamp, B, screw the cover over the wick 
and replace it in C. The whole of this apparatus 
fits into a circular tin case, 6 inches long, and 
2 inches in diameter. 
To use the boiling-point thermometer —Take 
the apparatus to pieces, pour some water into 
the boiler, D, about one quarter full is quite 
sufficient; then put the instrument together as 
shown in the drawing, taking care that the 
thermometer is just clear of the water, and 
light the spirit lamp; as soon as the water 
boils, the steam ascending through the tube, E, 
will cause the mercury to rise; wait until the 
mercury becomes stationary, and then read the 
thermometer; at the same time, take the tem¬ 
perature of the air in the shade with an ordinary 
thermometer. 
If the traveller is visiting a region where the 
elevations are very great, he should, when pur¬ 
chasing this apparatus, see that the thermo¬ 
meters are capable of registering a greater height 
than those which are usually supplied, and that 
the lamp is large enough to hold a good supply 
