206 Mr. C. Tomlinson's Experiments on the Electrical Fly, 



points will give off a stream of electricity \ this will remove a 

 part of the pressure which the fluid would have exerted on that 

 side if no efflux had taken place; but as the pressure of the fluid 

 on the opposite side of the wire in the opposite direction still 

 operates in full force, the wire will be impelled in the direction 

 of that force, that is, in a direction opposite to that of the stream ; 

 and this taking place at all the four points, the whole system will 

 revolve backward with considerable rapidity/' 



Becquerel* says, "The experiment of the electric fly shows 

 that the motion of bodies in electrical phenomena is really due 

 to the difference in pressure which the air exerts on all the points 

 of these bodies." Then, after describing the tourniquet, he 

 adds, "The electricity escaping by the points, the pressure 

 exerted by the air on the extremities being greatly diminished, 

 the needle turns in a contrary direction." 



Despretzf, after describing the fly, says, {l Ce phenumene est 

 absolument pareil a celui que nous avons observe pour lesliquides. ,} 



Lardnerf says, "When the electricity comes from the con- 

 ductor to the wires, it w T ill escape from the wires at these four 

 points respectively, and the force with which it leaves them will 

 be attended with a proportionate recoil, which will cause the wire 

 to spin rapidly on the centre." 



Harris §, speaking of the electrical aura or gale, says, "The 

 reactive force of this current upon the point itself, and from 

 which it appears to flow, is so great as to give the point motion 

 in a reverse direction when free to move." 



Biess || says, " This rotation arises from the mutual repulsion 

 of the electrified points and the particles of air" ^. 



De la Rive**, in 1853, though not altogether satisfied with it, 

 adopts the French theory as given by Biot in 1816. He says, 

 " In this experiment the electric fluid that is spread over the 

 stems of the mill exercises everywhere a pressure on the surround- 

 ing air ; if it found no escape, the opposite pressures being always 

 equal, the apparatus would remain at rest. But it escapes by 

 the points where it overcomes the atmospheric pressure ; and as it 

 no longer exercises any pressure on the orifice of escape, the 

 pressure which continues to be exercised on the opposite point 



* Traite experiment ale de V Electricite, vol. ii. (1834) p. 194. 



t Traite de Physique, fifth edit. Bruxelles, 1837, p. 271. 



X Manual of Electricity, &c. Cabinet Cyclopaedia (1841), vol. i. p. 330. 

 See also the Handbook of Natural Philosophy,' "Electricity," &c. (1856) 

 p. 62. 



§ Rudimentary Electricity, second edit. (1851), p. 151. 



|| Die Lehre von der Reibungselectricitdt (Berlin, 1853), vol. ii. p. 153. 



5T " Diese Rotation entsteht durch gegenseitige Abstossung der elektri- 

 sirten Spitzen und Lufttheilchen." 



** Treatise on Electricity. Translated by Walker (1853), vol. i. p. 130. 



