438 The Theory of Aether and Electrons in the 



charging, similar to that which would be produced if the mass 

 of a body at the surface of the earth were suddenly to become 

 greater. Moreover, it was conjectured that the condenser, 

 when freely suspended, would tend to move so as to assume the 

 longitudinal orientation, which is that of maximum kinetic 

 energy* : the transverse position would therefore be one of 

 unstable equilibrium. 



For both effects a search was made by Fitz Gerald's pupil 

 Trouton :f in the experiments designed to observe the turning 

 couple, a condenser was suspended in a vertical plane by a 

 fine wire, and charged. If the plane of the condenser were 

 that of the meridian, about noon there should be no couple 

 tending to alter the orientation, because the drift of aether due 

 to the earth's motion would be at right angles to this plane; 

 at any other hour, a couple should act. The effect to be 

 detected was extremely small ; for the magnetic force due to 

 the motion of the charges would be of order w/c, where w 

 denotes the velocity of the earth ; so the magnetic energy of 

 the system, which depends on the square of the force, would be 

 of order (w/c)' ; and the couple, which depends on the derivate 

 of this with respect to the azimuth, would therefore be likewise 

 of the second order in (w/c). 



No couple could be detected. As the energy of the magnetic 

 field must be derived from some source, there seems to be no 

 escape from the conclusion that the electrostatic energy of a 

 charged condenser is diminished by the fraction (w/c)" of its 

 amount when the condenser is moving with velocity w at 

 right angles to its lines of electrostatic force. To explain this 

 diminution, it is necessary to admit Fitz Gerald's hypothesis 

 of contraction. The negative result of the experiment may be 

 taken to indicate^ that the kinetic potential of the system, 

 when the Fitz Gerald contraction is taken into account as a 



* Larmor, in Fitz Gerald's Scientific Papers, p 566. 



t F. T. Trouton. Trans. Roy. Dub. Soc., April, 1902; F. T. Trouton and 

 H. R. Noble, Phil. Trans, ccii (1903), p. 165. 



J Cf. P. Langevin, Comptes Rendus, cxl (1905), p. 1171. 



