45 



rious combination inverted, that is, with a small copper ball in the 

 interior of a large hollow sphere of zinc ; and from these the author 

 concludes that, in this case also, the law of radiation is maintained, 

 although the force is reduced to one half of that obtained from the 

 former combination. 



In order to ascertain the effect of cutting off the lateral radiation 

 from the zinc ball, it was placed in a glass tube, six inches long, 

 within half an inch of the lower aperture, over which a piece of mem- 

 brane was tied, and the tube plunged into the solution of copper con- 

 tained in a brass hemisphere, so as to rest upon the bottom. The 

 results obtained by this arrangement, as also those when the zinc ball 

 was raised in the tube to the surface of the solution, showed that the 

 action of the zinc ball had been propagated from the aperture of the 

 glass tube, as from a centre, diverging from this in the solution. 



The experiments next described appear to have an important bear- 

 ing on a question of vital interest in the theory of electiicity, which 

 has been discussed by Air. Faraday, in a paper recently read to this 

 Society : viz., whether the forces emanating from a centre of electric 

 action act, like other central forces, in straight lines ; or whether 

 they are propagated from particle to particle in the surrounding mat- 

 ter, and may, consequently, when obstacles interfere with their 

 rectilinear propagation, exert their influence in curved lines. An 

 elliptical plate of copper, one side of which was covered with 

 lac varnish, was placed in an earthen pan, with the varnished 

 side upwards, and covered to the depth of a few inches ^vith 

 the acid solution of copper. The zinc ball, placed in the tube 

 half an inch from the diaphragm, was plunged just below the surface 

 of the solution, and the circuit being completed, the galvanometer 

 indicated an action nearly equal to that which had been previously 

 observed when both sides of the copper had been exposed. The 

 under side of the copper presented the appearance of a border of pre- 

 cipitated compact pink copper, varying from 14- to -|- of an inch in 

 width, and the remainder was covered with precipitated copper of a 

 darker red colour, into which the border gradually passed; and similar 

 results were obtained with a circular disc of copper, having one side 

 varnished. It hence appears, that the under surface, which, by itself, 

 is capable of sustaining from the ball in the centre of the solution an 

 action nearly as great as the upper surface, when combined with the 

 latter adds no more than about one- eighth part of its efficiency ; and 

 whereas, with the upper surface, the action varies in some inverse 

 ratio of the distance of the generating from the conducting surface, 

 vrith the under surface, there is a maximum point, on both sides of 

 which it decreases : and this point is doubtless dependent on the 

 angle at which the force v\'hich radiates from the ball meets the edge 

 of the plate. The author having been led to the conclusion, that the 

 force developed by voltaic combinations is subject to the law of ra- 

 diant forces, had been utterly at a loss to understand how, upon this 

 hypothesis, it could extend its influence to the side of a plate oppo- 

 site to that to which it was directed in right lines ; but having per- 

 used Mr. Faraday's " Eleventh series of experimental researches in 



