MR. DANIELL ON VOLTAIC COMBINATIONS. 45 



For this purpose I made use of the calorific galvanometer (as it has been named by 

 M. De la Rive,) instead of the magnetic ; and the zinc ball was a little larger than 

 in the preceding experiments, measuring 1 J inch in diameter, and presenting therefore 

 a surface of 3'94 square inches. The sphere was charged as before, and when the 

 ball was placed in the centre 



The index advanced 90 



When drawn nearly to the top .... 90 

 When thrust nearly to the bottom ... 87 



The index remained perfectly steady during several repetitions of the experiments ; 

 and when the connexion with the brass sphere was changed to opposite points. 

 There can be no doubt that these results indicate the same equality of action as be- 

 fore ; the slight difference in the lower position being, probably, owing to accidental 

 circumstances, such as the unequal thickness of the membrane at that point, or the 

 speedy saturation of the acid when the solution cannot fall away from the zinc. 

 Thus it would appear, that in none of these positions was there any virtual approxi- 

 mation of the generating and conducting surfaces. The diffusion of the precipitated 

 copper was, however, very much influenced by the position of the ball ; when near 

 the top or the bottom, it was thrown down in a compact layer on a segment imme- 

 diately in its vicinity, and became thinner and thinner over the more remote parts of 

 the sphere. It was only when exactly in the centre that the diffusion was perfectly 

 equal. To observe this effect with the greatest distinctness, the action in each case 

 should not be allowed to continue more than ten or fifteen minutes ; for the deposi- 

 tion becomes compact in every part in a longer time, when it is not so easy to judge 

 of the difference of thickness. 



My next step was to measure the effects of different portions of the sphere in com- 

 bination with the zinc ball. I took the lower hemisphere alone of the apparatus and 

 filled it with the solution of copper, and placing a wooden bar across it which sup- 

 ported the membranous bag to carry the acid, I had it in my power to immerse the 

 ball in any required position. 



I first placed the same ball as in the last experiment just below the surface exactly 

 in the centre, and the calorific galvanometer indicated 90°: upon removing it within 

 half an inch of the bottom it rose to 115°. 



On another occasion I placed the ball in three different positions upon the surface 

 of the liquid in the hemisphere, namely, in the centre and close to each side : in 

 each position the instrument marked 86°. Upon Ipwering it as close as possible to 

 the bottom it rose to 100°. In all these experiments the precipitated copper was dif- 

 fused over the whole hemisphere. 



It is worthy of remark, that the amount of force thus called into action at the 

 surface of the liquid in the hemisphere, is nearly the same as that from the whole 

 charged sphere, or either of its hemispheres. 



These results, I conceive, are not in opposition to the law of radiant forces sug- 



