»< barus.] VISCOSITY OF GASES. 241 
Jlomb's method of vibrating plates, a method which does not serve well 
for the determination of the thermal relations of mean free path, although 
it has been applied with this end more or less fully in view by Meyer, 1 
by Maxwell 2 himself, by Puluj, 3 and others. Among these observers 
only Puluj, using an apparatus devised by Kundt and Warburg, suc- 
ceeded in deriving good results. Very important service was therefore 
done to this branch of molecular kinetics by the elaborate researches 
of O. E. Meyer. 4 Availing himself of the general differential equations 
for the motion of a viscous fluid published by Stokes, 5 or those more 
recently published by Stefan, 6 O. E. Meyer deduces the well-known 
equation, in which the rate of transpiration is fully expressed in terms 
of the terminal pressures, the viscosity of the gas, the coefficient of 
external friction, and of the dimensions of the capillary tube through 
which the gaseous flow takes place. Calculating from this result the 
volume of gas transpiring during a given time, under given conditions, 
Meyer reaches a result which, for gases, is the complete analogue of the 
law for liquids experimentally deduced by Poiseuille 7 and flagen, 8 and 
to which Stokes 9 and others (Neumann, Wiedemann, Hagenbach, Ste- 
fan, Helmholtz) have given a theoretical foundation. It is by using 
this equation that Meyer 10 himself, discussing Graham's results, in later 
work, 11 partly in conjunction with Springmiihl, 12 derived the first good 
results for the thermal coefficient of viscosity. Such results have since 
i been obtained in greater number and with greater elegance in transpi- 
i ration experiments, made by Puluj, 13 v. Obermayer, 14 E. Wiedemann, 15 
Warburg, 16 Schumann, 17 and particularly by Holman, 18 to whose elegant 
and elaborate researches I have already referred. 
In all of these cases, however, the data in hand are essentially low- 
temperature results. The largest range of temperatures occurs in 
Obermayer's later research, in which the thermal relations of the vis- 
l O. E. Meyer: Pogg. Ann., vol. 125, 1865, p. 177 ; 5th series, vol. 23, 1871, p. 14. 
- Maxwell : Phil. Trails., 1866 (I), p. 249. 
3 Puluj: Wieii. Sitznngsber., vol. 73 (2), 1876, p. 589. 
4 O. E. Meyer: Pogg. Ann., vol. 127, 1866, pp. 253,353. 
^ Stokes: Trans. Cambridge Philos. Soc., vol. 8, 1847, p. 287. 
e Stefan: Wien. Ber., vol. 46 (2), 1862, p. 8. 
7 Poiseuille: Mem. Sav. Strang., vol. 9, 1846, p. 433; Ann.cb. et pbys. (3), vol. 7, 
1843, p. 50. 
sHagen: Abb. d.JBerl. Akad., 1854, p. 17. 
9 Stokes: Trans. Cambridge Pbilos. Soc., vol.8, 1847, p. 287. 
10 Meyer: Pogg. Ann., vol. 127, 1866, p. 367. 
11 Meyer: Pogg. Ann., vol. 148, 1873, p. 1 ; ibid., p. 203. 
13 Meyer u. Springmiihl: ibid., p. 503. 
I 3 Puluj : Wiener Sitznngsber., vol. 69, p. 287 ; vol. 70, p. 243, 1874. 
14 V. Obermayer: Wiener Sitzungsber., vol. 71, 1875, p. 281 ; vol. 73, 1876, p. 433. 
15 E. Wiedemann : Fortsckr. d. Physik, vol. 32, 1876, p. 206. 
1,3 Warburg: Pogg. Ann., vol. 159, 1876, p. 403. 
17 O. Schumann: Wied. Ann., vol. 23, 1884, p. 353. 
18 Holman : Proc. Ann. Acad. Arts and Sci., vol. 12, 1876, p. 41 ; ibid., vol. 21, 1886, p. 1. 
Bull. 54 16 (895) 
