The Theory of the Small Ion in Gases. "817 



the mirrors on long rods, but the mirrors would have to be 

 a long way below the roof and above the ground. Of course, 

 if P is infinite, or nearly so, the roof would screen off the 

 aetherial stream, which would go down the walls supporting 

 the roof into the earth. It is remarkable tbmt two theories 

 like the present one and the accepted theory of a stagnant 

 aether both appear capable of accounting for ail the facts, and 

 that it is difficult to see how to devise a crucial experiment. 

 Under these circumstances all that can be said is that the 

 theorv here proposed does not involve the existence of the 

 complicated second order compensations which appear to be 

 necessary it' the aether is stagnant, even for the explanation 

 of the motion of a system in a straight line with uniform 

 velocity. 



If the aether is really absolutely stagnant, it is difficult to 

 see how any phenomena can take place in it. 



LXXXII. The Theory of the Small Ion in Gases. 



To the Editors of the Philosophical Magazine, 

 Gentlemen, — 



IN the Phil. Mag. of January Mr. Wellisch raises certain 

 points to show that they tend to support his form of the 

 theory of the small ion rather than mine. We agree about 

 the small ion's not consisting of a cluster of molecules, but 

 resembling rather the ion of the ordinary theory of electrolytic 

 solutions. Mr. Wellisch holds that the effect of the cluster 

 is caused by the increase of the ordinary frictional resistance 

 to the motion of the ion caused by its electric attraction of 

 the molecules of the gas. The view which I take is that 

 besides this effect of electrical attraction there is a dissipative 

 frictional force caused by it, one of two now types of viscosity, 

 whose retarding effect must be added to that of the ordinary 

 collisional viscosity. Mr. Wellisch points out that one of the 

 theoretical formulae for the resistance to the motion of a 

 spherical molecule or ion amongst other molecules make- it> 

 amount larger than that given by the formula which 1 used. 

 With the larger ordinary resistance furnished by that formula, 

 and with a large increase of that ordinary resistance brought 

 about by electric attraction in the way in which he calculates 

 it, Mr. Wellisch does not need any viscositv of electric origin 

 to explain the experimental magnitude of the mobility of the 

 ions in the commoner gases. Concerning the different nume- 

 rical coefficients yielded by different methods of handling 

 the kinetic theory of spherical molecules, ir is probable that 

 physicists will ultimately be decided in their choice by the 

 one that applies over the greatest range of experimental 

 Phil. May. S. 0*. Vol. 19. No. 113. May 1910. 3 G 



