502 II A. Bumstead — lorentz-Fitz Gerald Hypothesis. 



It is scarcely necessary to point out that such problems as 

 we have been considering do not lead to any practicable 

 experimental tests. In order to detect deviations, it would be 

 necessary to measure the periods in question with an accuracy 

 such that the errors should be less than 10~ s , which is quite 

 out of the question at present. This does not however affect 

 the legitimacy of the use of such methods in following out the 

 consequences of the principle; just as the impossibility of 

 actually constructing a reversible engine does not invalidate 

 that method of applying the second law of thermodynamics. 

 More general methods might be used ; but there is some 

 advantage, especially in a comparatively new subject, in the 

 simplicity and concreteness of ideas derived from the consid- 

 eration of special problems. 



Applications to Gravitation. 



A promising direction in which to look for possible tests of 

 the hypothesis is among the consequences of the deduction 

 that gravitational forces must vary with motion through the 

 ether in the same manner as electrical forces. If we have a 



Fig. 2. 







W> 



E, 



p 







/e 



— * — 









point charge e moving alone the axis of a?, with the uniform 

 velocity v, the electric intensity at a point P whose coordinates 

 are r, 6 is 



E=v * 'd-* 1 ) , r _ (1) 



r 2 (l -/3 2 sin 2 0)f x V ; 



,v 

 where r x is a unit vector in the direction of r and /3— — .* The 



magnetic force is perpendicular to the plane of r and v and 

 has the magnitude 



V ! r 2 (i _ p* sin 2 0), 



* Electromagnetic units are used. 



(2) 



