351 
If we except nitrogen, nitrous oxide and cyanogen, the approach 
towards constancy seems remarkable. Considering the imperfect 
nature of the data at our disposal the agreement between the values 
of the product vA seems as close as could have been expected. If 
we confine ourselves to the following gases: 
H 2 , 0 2 , Air, CO, C0 2 , NH 3 , CS 2 , S0 2 
we find the mean of the values of vA to be 16,3. It is much to 
be desired that new experiments be made from which the exact 
value of this constant could be deduced. 
The next remark called for by the inspection of the table is 
that there are undoubtedly cases in which the rule fails, nitrogen 
being a conspicuous example; the behaviour of N 2 0 and of C 2 N 2 
is-perhaps less surprising. We think it would be premature to dwell 
on the explanation of these anomalies; we cannot but feel that the 
law enunciated in this § rests upon a foundation of truth allthough 
it appears to be subject to restriction vhen expressed in the rough 
form which unfortunately was the only one we have been able to 
verify. 
§ 25. In the paper quoted Drude has called attention to the 
fact that the value of the quantity e/m which can be deduced from 
the Electromagnetic Theory of Dispersion does not agree very 
exactly with the accepted value of this constant 1 ). From (1), § 24., 
the same result can be obtained. If we assume 
e M (0° C., 760 mm.) = 1,29.10 10 gm 1/a cm -3 ' 2 sec -1 (1) 
we have (in electromagnetic units) 
e_ 21.918. 10 7 
m [a A] ^ 
where [a A] is the value of the supposed constant expressed in 10~ 7 cm 2 . 
Substituting 16,3 for [a A] we find 
- = 1,34.10’. (3) 
m w 
In order to arrive at 1,865.10 7 , the value of e/m generally accep¬ 
ted on the authority of Kaufmann. Seitz, Simon and Starke, we 
would have to assume [aA\ = 11,75. 
1 ) cf. J. Koch, Annalen d. Physik, Bd. 17 ., p. 665. 1905. 
