barus.] VISCOSITY OF GASES. 295 
Table 103. — Differential measurement. Apparent viscosity of air at high temperatures. 
« 
[Capillary tubes Nos. 5 and 6. Z'-f V" = 4 cm . Z" = 30.4<=™. L=41.2* m . B= 0.0184 cm . Thermo-couple 
No. 37. = 4°.] 
p-p 
7h 
y e 
e" 
P 
P 
Ph/i?g 
39.9 
43.8 
52.5 
4 
117.4 
77.5 
1.00 
10.7 
44.7 
52.2 
4 
88.2 
77.5 
1.03 
10.7 
10.8 
43.3 
43.6 
51.9 
52.1 
4 
4 
88.2 
88.3 
77.5 
77.5 
1.00 
1.00 
39.8 
44.4 
51.3 
4 
117.3 
77.5 
1.04 
P-P 
7h 
Fg 
F(6") 
0" 
P 
P 
V 
'+$ 
44.0 
51.2 
16.2 
1.38 
587 
121.5 
77.5 
0. 000362 
0. 000501 
11.9 
51.9 
12.2 
1.78 
605 
89.4 
77.5 
259 
461 
44.6 
51.0 
15.4 
1.37 
614 
122.1 
77.5 
364 
498 
11.7 
52.1 
11.5 
1.86 
624 
89.2 
77.5 
258 
480 
44.5 
51.3 
14.9 
1.40 
630 
122.0 
77.5 
363 
508 
44.7 
51.6 
9.54 
1.61 
973 
122.3 
77.6 
0. 000364 
0. 000587 
11.7 
52.5 
7.22 
2.17 
974 
89.3 
77.6 
258 
560 
44.8 
52.1 
9.51 
1.63 
977 
122.4 
77.6 
364 
593 
11.4 
52.8 
7.05 
2.23 
977 
89.0 
77.6 
257 
574 
45.2 
51.5 
9.40 
1.63 
978 
122.8 
77.6 
365 
596 
11.5 
52.4 
6.96 
2.24 
979 
89.1 
77.6 
258 
578 
It was not my object in this place to carry this method to a high de- 
gree of perfection, but rather to show the feasibility of measuremeuts 
made in this expeditious aud simple way. This the tables effectually 
do. Table 101 shows that for tubes of the large radius jR=0.025 cm the 
results are not accurate when so small a volume as F=50 cc transpiring 
at zero, is made the standard of comparison. They are irregular. On 
the other hand, when the standard volume transpires at high tem- 
peratures (0=900° and 6">6), this method proves to be quite feasible 
aud the results regular (Table 102). For tubes of finer bore (i£=0.018 cm ), 
Table 103 shows that the data are consistent at all temperatures. 
Fortunately, in the differential method the errors due to the dead 
space between stop-cock and the capillary, if this space be made small, 
is nearly eliminated. 
DISCUSSION. 
Apparent viscosity and pressure. — To obtain a clear insight into the 
data of these tables, it will be necessary to construct them graphically. 
This has been done in Fig. 54, p. 304, in which the abscissae are P— p, 
and the ordinates the value of t/" given by the Poiseuille-Meyer formula, 
by inserting in it the given constants of the apparatus and the value of 
the pressure, time, and volume data observed. Commencing with Table 
(949) 
