MONATOMIC GAS: DIFFUSION, VISCOSITY, AND THEEMAL CONDUCTION. 177 
probably little more knowledge would be gained from it than may be deduced from 
the above discussion and from Table IV. of § 13 (i). 
( i) Variation of D 12 with v r : v 2 . Comparison with Experiment. 
In view of the conflicting theories regarding the relation between I) I2 and i>Jv 2 , 
several series of experiments to test the question were made at Halle during the years 
1904-1909, under the direction of Prof. E. Dorn.* The gases used were helium 
argon by Schmidt and Lonius, oxygen—hydrogen by Deutsch and Jackmann, 
carbon dioxide—hydrogen and oxygen—-nitrogen by Jackmann. In Jackmann’s 
summary of the experiments it is pointed out that the observed variations in D 12 , 
though far from negligible, are small compared with those predicted by Meyer’s 
theory, while Gross’s theory (cf § 13 (g)) is equally unsuccessful in that it predicts 
variations of the right order hut in the wrong direction. 
Jeans! compares these observations both with Meyer’s theory and with the 
corrected form of Meyer’s theory after allowing for the persistence of velocities 
( cf. § 13 ( g ). The following table is taken from § 446 of his treatise (2nd edition), 
and relates to the pair of gases, helium—argon :— 
Table IV.—Variation of D 12 for He-A. 
D 12 observed 
(Schmidt and Lonius). 
Dio (calculated). 
Meyer’s theory. 
Meyer’s theory oorrected 
(Jeans, Kuenen). 
2-65 
0-961 
0-548 
0-910 
1-00 
1-000 
1-000 
1-000 
0-31 
1 -036 
1*526 
1-110 
In this table the values of D 12 have been multiplied by a factor in order to make the 
value corresponding to = v 2 equal to unity, for convenience of comparison. Jeans 
remarks, a propos of the above table, that the observed variations of D 12 are 
insignificant compared with those predicted by Meyer’s theory, being small even 
compared with those predicted by the corrected theory, and that Maxwell’s simpler 
formula (according to which D 12 is independent of vfv^) is after all the most accurate 
numerically. We shall see, however, that the present theory, with its correction 
V'/V to the usual first approximation (13'06) to D 12 , gives results which are in much 
closer accordance with the observed phenomena. 
* Schmidt, ‘Halle Dissertation’ (1904), and ‘Ann. d. Phys.,’ 14, p.801, 1904; Deutsch, ‘Halle,’ 
1907 ; Jackmann, ‘Halle,’ 1906; Lonius, ‘Halle,’ 1909, and ‘Ann. d. Phys.,’ 29, p. 664, 1909, where 
the results of the whole series of experiments are summarised arid discussed. 
t Jeans’ ‘ Dynamical Theory of Gases ’ (2nd ed.), § 446. 
