3ARUS.] 
VISCOSITY OF GASES. 
247 
pass around the thermometer in the tube 
T, and thence by the lateral tube h into 
the capillary apparatus. This is shown 
in side elevation in Fig. 45 and in plan in 
Fig. 46. The figures are sectional, and 
the lettering of Fig. 43 is retained. The 
scaffolding and n on essential parts are 
emitted. Regarding this figure in its gen- 
eral purposes, I will say here that there 
are three ways in which viscosity has 
been measured: 
1. By measuring the time of efflux of 
the fixed volumes of air in B through the 
capillaries. 
2. By measuring the rate at which air 
passes out of the capillaries. 
3. By differential methods. 
The first of these methods is not gen- 
erally as convenient as the second, be- 
cause the volume of B is relatively large, 
and the time of efflux may become enor- 
mously large. Hence in my final experi- 
ments I used the second method, and it 
is to this that the present description 
largely applies. The gas enters from the 
tube Jc (Fig. 45) through the stop cock IT, 
thence it passes through the tube g li into 
the coil of platinum capillary tube J, and 
out of this into the graduated tube llll, 
filled with water. Here it is measured. 
The tube llllis simply an inverted bu- 
rette of about 50 cc capacity. After fill- 
ing it with gas and taking the observa. 
tion it is made ready at once for the next 
experiment by sucking the water out of 
the pneumatic trough M M up into the 
tube through the stop-cock o and closing- 
it. To insure constancy of temperature 
this tube I III is jacketed by a larger 
tube, ii i i, through which a rapid current 
j of water, entering by the tube p t, con- 
! tinually circulates. The water escaping 
from the bottom of i i i i keeps the trough 
MM full of cold water, and finally escapes 
by the lateral efflux pipe X. The upper 
vertical tube q is used in filling i i i i with 
. (901) 
7 
Af 
\K 
Af~k 
Fie. 45. Side elevation of capillary ap- 
paratus. Scale £. 
