3ARUS.J 
VISCOSITY OF GASES. 
265 
registered temperature at the outside of the helix continues to increase 
long after the internal and registered temperature is practically station- 
ary. The mean temperature of the helix is thus still on the increase, after 
the temperature of the thermo-couple is constant, and the discrepancy 
in question points out an ordinary phenomenon of heat conduction. All 
these peculiarities appear clearly in Fig. 48, where points dashed up- 
ward refer to hydrogen, points dashed downward refer to air. Leaving 
the exceptional values out of consideration, the data of these tables are 
of special importance. They show that the locus F{8") does not only 
lie below (1+a #")*, but that its value is most probably (l+« ■ S")%. 
Indeed, the close coincidence of the data between 400° and 800° with 
the function (1+a 6")% is an exceedingly striking observation. When 
it is called to mind that theoretical reasons suggest the exponential 
r 
form (l+« 6") n , that the effect of slip 1+4 „ is in the opposite sense 
to the necessarily negative error in 6", then the acceptation of 
(l+«0")3as the simplest convenient expression for the co-ordination 
of all the data F(6") is easily justified. 
Tables 81 to 84 have proved beyond a doubt that the predominating 
error in the present experiment is introduced by the fact that the mean 
temperatures of the viscosity pyrometer and of the thermoelement are 
essentially different. The degree of constant temperature throughout 
the space occupied by these two instruments is therefore by no means 
sufficient ; hence I made a few measurements on the effect produced by 
changing the position of the thermo-couple and of enveloping the helix 
with layers of a nonconducting material. ' I also endeavored to test in 
how far a more reliable temperature datum could be obtained from the 
simultaneous indications of two or more thermo couples touching dif- 
ferent points on the inside and on the outside of the helix. 
Table 85. — Viscosity of air. Miscellaneous tests. 
[Capillary tube No. 10. £=33.43 CD >. l'+l"'=4A^ ij =0.0002472. 0=6^. 
J K=0,00794 cn >.] 
p 
P 
t" 
To 
0" 
7)" 
F(6") 
1+4^/P 
I. 
-Therm 
o-couple 
nearly i 
laked. 
123. 11 
75.93 
170 
51.35 
5 
0. 0002497 
123. 13 
75. 93 
170 
51.35 
5 
2499 
123. 15 
123. 17 
123. 17 
124. 29 
75.93 
75.' 93 
75.93 
75.80 
170 
170 
170 
1S00 
51.40 
51.38 
51.38 
51.60 
5 
5 
5 
1055 
2497 
2500 
2500 
0. 0006716 
2.717 
124. 31 
75.80 
1950 
51.60 
1040 
7359 
2. 977 
124. 30 
75.80 
1845 
51.00 
1062 
6933 
2. 805 
124. 17 
75.89 
2460 
50.96 
1347 
0. 0007684 
3.109 
124. 22 
75. 82 
24G0 
50.50 
1338 
7813 
3. 161 
124. 27 
75.79 
2460 
50. 39 
1336 
7852 
3.177 
(919) 
