70 Royal Society : — 



ing the ball, the material of which the ball is made, and a very- 

 slight difference between the temperatures of the mass and the 

 ball, exert so strong an influence over the attractive and repulsive 

 force, and it has been so difficult for me to eliminate all interfering 

 actions of temperature, electricity, &c, that I have not yet been 

 able to get distinct evidence of an independent force (not being of 

 the nature of heat) urging the ball and the mass together. 



" Experiment has, however, showed me that, whilst the action is 

 in one direction in dense air, and in the opposite direction in a 

 vacuum, there is an intermediate pressure at which differences of 

 temperature appear to exert little or no interfering action. By 

 experimenting at this critical pressure, it would seem that such an 

 action as was obtained by Cavendish, Eeich, and Baily should be 

 rendered evident." 



After discussing the explanations which may be given of these 

 actions, and showing that they cannot be due to air-currents, the 

 author refers to evidences of this repulsive action of heat, and at- 

 tractive action of cold, in nature. In that portion of the sun's 

 radiation which is called heat, we have the radial repulsive force, 

 possessing successive propagation, required to explain the pheno- 

 mena of comets and the shape and changes of the nebulae. To 

 compare small things with great — to argue from pieces of straw up 

 to heavenly bodies — it is not improbable that the attraction, now 

 shown to exist between a cold and a warm body, will equally prevail 

 when, for the temperature of melting ice is substituted the cold of 

 space, for a pith ball a celestial sphere, and for an artificial va- 

 cuum a stellar void. In the radiant molecular energy of cosmical 

 masses may at last be found that " agent acting constantly accord- 

 ing to certain laws," which Newton held to be the cause of gravity. 



January 8, 1874, — Joseph Dalton Hooker, C.B., President, in 

 the Chair. 



The following communication was read : — 



" On Electrotorsion." By Greorge Grore, F.B.S. 



This communication contains an account of a new phenomenon 

 (of rods and wires of iron becoming twisted while under the in- 

 fluence of electric currents), and a full description of the con- 

 ditions under which it occurs, the necessary apparatus, and the 

 methods of using it. 



The phenomenon of torsion thus produced is not a microscopic 

 one, but may be made to exceed in some cases a twist of a quarter 

 of a circle, the end of a suitable index moving through a space of 

 80 centimetres (=31 inches). It is always attended by emission 

 of sound. 



The torsions are produced by the combined influence of helical 

 and axial electric currents, one current passing through a long 

 copper-wire coil surrounding the bar or wire, and the other, in 

 an axial direction, through the iron itself. The cause of them is the 

 combined influence of magnetism in the ordinary longitudinal direc- 



