132 Prof. F. T. Trouton and Mr. H. R. Noble. [June 11, 



"The Forces Acting on a Charged Condenser moving through 

 Space." By Professor F. T. TKOUTON, F.R.S., and H. R. NOBLE, 

 B.Sc., University College, London. Received June 11, 

 Read June 18, 1903. 



(Abstract.) 



If a charged condenser be placed with its plane in the direction of the 

 sether drift, then on the assumption that a moving charge develops a 

 magnetic field, there will be associated with the condenser a magnetic 

 field perpendicular to the lines of electric induction, and to the direction 

 of the motion. If N be the electrostatic energy of the condenser, 

 the magnetic energy produced when moving with velocity w through 

 the aether with its plates parallel to the motion is N (w/v) 2 , where 

 v is the usual velocity of propagation. But when the plates of the 

 condenser are perpendicular to the direction of motion, the effects of the 

 opposite charges will neutralise each other, and there will be no 

 magnetic field produced. Thus if we have a condenser freely suspended 

 with its plates making an angle ^ with the direction of the aether drift, 

 the magnetic energy is N (w/v) 2 cos 2 ^. The couple tending to increase 

 ^ is - dE/d\/;, which is N (w/v) 2 sin 2 ^. By utilising the Earth's 

 motion through space, we can arrange (generally) the experiment so 

 that ^ = 45 and w is the total velocity of the Earth through space. 

 The couple is then a maximum equal to 10~ 8 N for the orbital 

 velocity alone, and to 2*3 x 10~ 8 N when we include the Sun's proper 

 motion. 



A condenser was suspended by a fine wire and charged. The charges 

 were let into the plates of the condenser by means of this suspending 

 wire, and by a wire which hung from beneath dipping into a liquid 

 terminal. Observations were made at different times in the day when 

 the plane of the condenser made various angles with the direction of the 

 drift. 



The final form of the apparatus is as follows : The suspension is a 

 phosphor bronze strip 37 cm. long, the finest that could be obtained. 

 This was soldered at its lower end A to a copper cap, fixed to the 

 condenser protecting the projecting tin foil tags and making contact 

 with them by means of fusible metal. The upper end of the suspension 

 was wound on a small windlass which was insulated by a mica plate 

 fixed to an annular wooden ring, forming the lid to the inner zinc 

 vessel. A small glass bell jar covered the windlass, contact being 

 made by a wire passing through the small cork at the top. A small 

 brass tube shields the upper part of the suspension, and a thin metal 

 cylinder protects the point of support. The condenser is inserted in 

 a celluloid ball, to diminish the effect of convection currents. Two 

 cylindrical zinc vessels protect the apparatus, the interspace being 



