852 Mr. E. W. B. Gill : Comparison of 



complain if mass turns out to be a length when we announce 

 that matter is a system of electrons whose mass becomes 

 infinite if it moves with the velocity of light ? 



To the man of simple mind, the situation in science to-day 

 is marvellously like that during the struggle between Galileo 

 and the mediaeval schoolmen. Galileo won because he held 

 fast to the belief that men of science must deal with a sensible 

 world and not with a phantasmic system of intricate logic. 

 If the age of Galileo seems -outworn as an example, there is 

 also the conviction of Faraday that science has always had 

 the task of u repressing and dissolving the phantoms of the 

 imagination." The cost of thrusting us into a continuum of 

 four dimensions where time is confused w T ith space and the 

 velocity of light in vacuo is our foot-rule in order that we 

 may solve logically a few comparatively insignificant phe- 

 nomena is too great. 



Cincinnati, 8 March, 1921. 



XCII. Comparison of Processes of Ionization which give rise to 

 Currents in Gases. By E. W. B. Gill, ALA., B.Sc, 

 Fellow of Alert o-?i College, Oxford*. 



1. rjlHE experimental verification of the theory of 

 JL ionization by collision given by Professor Townsend 

 depends principally on the comparison of the currents 

 obtained between parallel plates with the formula for the 

 currents calculated on the hypothesis that all the new ions 

 are generated in the gas by the collisions of electrons or 

 positive ions with molecules of the gas. 



With a view of finding to what extent the quantum theory 

 of radiation may be applied to effects produced by collisions 

 with molecules, a large number of experiments have recently 

 been made to determine the minimum potential required to 

 ionize a molecule of gas by collision, and the minimum 

 potential required to excite radiation by impacts between 

 electrons and molecules ; which radiation has the effect of 

 setting free electrons from a metal electrode. The latter 

 potential has been found to be the smaller of the two, 

 so that in many cases in which the additional currents have 



* Communicated bv Prof. J. S. Townsend. F.E.S. 



