Stoney — On Double Lines in the Spectra of Gases. 203 



shifted round with an apsidal motion that carries it once round 

 while the electron performs 1984 of its little elliptic revolutions. 

 It further appears from the observations that in this case the 

 direction of the apsidal shift is the same as the direction in which 

 the electron revolves in the ellipse. These events occur with such 

 extraordinary rapidity within the molecules of sodium, that slow 

 as the apsidal circuits seem when compared with the much swifter 

 revolutions of the electron, there is time for something like 36 of 

 them to be completed within the average duration of the flights of 

 a molecule between its encounters with other molecules, assuming 

 (as is indicated by the kinetic theory of gases) that it is exposed to 

 about 7000 millions of these encounters every second. 



