49$ II. A. Bumstead — Lorentz-Fitz Gerald Hypothesis. 



quences. This will doubtless lead to further experimental 

 tests ; and even apart from direct tests, one may regard the 

 evidence for the principle as being strengthened if it intro- 

 duces simplification and harmony into the theory of phenom- 

 ena which are apparently remote from those that led originally 

 to its adoption. 



As the dimensions of all bodies are altered by motion 

 through the ether, it is plain that such motion must be taken 

 into account in the exact theory of even purely dynamical 

 phenomena. As such applications are not very familiar and 

 present some points of interest, it seems not altogether super- 

 fluous to consider a few very simple dynamical cases from this 

 point of view. 



The Torsion Pendulum. • 



Suppose a bar of length L (when at rest) hung up by a 

 torsion wire in the ordinary way. Let the apparatus be car- 



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B ^>^ 





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// ' \\ 

 / i \\ 



/ i \^ 

 I i \ 





i \\ 



i \ 



i M * 







M,J 



ried by the earth through the ether with the velocity v in a 

 direction perpendicular to the wire ; and let us consider the 

 period of the pendulum when the bar is clamped to the wire 

 in two different positions : (1) with its length perpendicular to 

 the earth's motion, and (2) parallel to the direction of motion. 

 By the principle of relativity the two periods must be equal. 

 As, the length of the bar in the first position is L and in the 

 second position Vl — /3 2 L, it appears at first sight that the mass 

 of every particle of the bar should be greater in position (2) 

 when it is moving perpendicularly to the earth's motion than 

 in (1) when it is moving parallel to it. This would make the 



