BAKis.i VISCOSITY" OF GASES. 255 
Finally, if 8=6" equation (6) furnishes a very simple equation for the 
ratio of radii of capillary tubes. For if t=t c 
22" V VL 
(?) 
a relation which is frequently of use. 
EXPERIMENTAL RESULTS. 
Manipulation. — In describing the present series of experiments it will 
be advisable to proceed somewhat explicitly ; for the methods were fre- 
quently varied, and variations of an apparently trifling kind were fre- 
quently found of great practical importance. Neither is it expedient to 
retain wholly the chronologic order of experiment. The following tables, 
81 to 89, represent a connected series of experiments, in which the method 
used is gradually perfected, and in which the data therefore approach the 
true law of variation more fully as the experiments proceed. 
In making these experiments the apparatus, Figs. 44 to 46, was used. 
The air which had transpired was therefore caught after efflux from the 
capillary tubes. Inasmuch as the receiver B is very large (550 cc ) and 
transpiration through the capillary tube takes place at a very slow rate, 
almost no effect is produced in the pressure of the gas in B when the 
cock K (Figs. 43, 46) is opened. This is a great convenience in manipu- 
lation and suggests the following scheme of operations : Suppose the 
Mariotte flask to be in its lowest position on the standard, aaaa bbbb, 
all cocks except K open, and the Mariotte uncorked. Mercury will then 
have run back into A, and the reservoir B will be filled with dry air. 
Now, close the cocks G and 8 and cork the Mariotte. Hoist the flask A 
to the level above B desired, and clamp it. Open G slightly at first 
until the mercury is seen just above D and then close D. Mercury will 
then flow into B through P U Q (the cock G being now fully open) until 
the maximum pressure is registered by the manometer R R'R'. Both 
the lower and upper meniscus of this are read. The gas in B is therefore 
practically under the pressure under which it is to be passed through 
the capillaries. Inasmuch as the volume of B is more than ten times 
as large as the volume to be measured after efflux, the pressure appa- 
ratus is ready for a number of consecutive experiments. After the 
receiver is quite filled with mercury and the cock JT is closed, G is closed 
also and the Mariotte flask is lowered and unstopped. D is now opened 
and G is opened cautiously, so as to take the pressure out of the ma- 
nometer. After this is done S is opened, whereupon G may be fully 
opened and the mercury thus flows back to A, while B fills with dry 
air. The operations are then repeated and the gas in B is put under 
pressure for the next ten experiments. This is the mode of experimen- 
tation in the main, although accidents or divers special purposes suggest 
slight variations of it. It is desirable to draw no air through the ma- 
(909) 
