CHAPTER XII. 

 INCREASE OF INERTIA DUE TO VERY RAPID MOTION. 



THE hypothesis to which we have been led is that 

 the inertia of an electron is wholly of an electrical 

 character, and is explained by the known magnetic 

 effect of an electric charge in motion, and the con- 

 sequent reaction to any change in that motion. 



Usually inertia is treated as constant and quite 

 independent of speed ; but now arises the question 

 whether the distribution of charge on a charged body, 

 together with its lines of force, will remain constant 

 and unaltered while the body is rapidly moving ; 

 because if the distribution of lines of force is altered, 

 then the inertia due to their lateral motion will 

 probably be altered too. This can be made plain 

 after referring back to Chap. II. 



Thus, for instance, imagine that the lines of electric 

 force of a body in motion became more concentrated 

 towards the axis or line of motion ; the effect would 

 be at once to diminish the lateral component of their 

 motion, therefore to diminish the magnetic force which 

 that lateral component causes, and thus to diminish 

 the apparent or electromagnetic inertia of the moving 

 charge. 



On the other hand, if the lines opened out and 

 became concentrated towards the equator, or plane 



