of Substances upon Voltaic Action. 457 



was compared with that of the usual copper bars, the sur- 

 faces of each pair being -£$ inch from the axis of the 

 electrodes. The result of this experiment was that the 

 sheets gave somewhat less than one-half — viz. a proportion 

 of .1-0 to 2*69— of that of the bars, but a much larger pro- 

 portion than that which was due to their relative mass, which 

 was 1*0 to 153*84, doubtless because their mean distance was 

 much less than that of the bars, viz. as 10 to 8*838 from the 

 surfaces of the electrodes. The influence therefore came 

 from the internal mass of the influencing substance as well as 

 from its superficial particles, and -so far agrees with the action 

 of gravity. - - • . ■ v 



Influence of Distance. 

 The only experiments on the influence of distance of the ; 

 bars from the electrodes were made with a pair of bars of> 

 wrought iron of "the usual dimensions. With the nearest 

 surfaces of the bars at a distance of ^ i ncn from the 

 axis of the electrodes, and at jj inch, the numbers ob- 

 tained were respectively 63-06 and 20*31, the latter being 

 considerably greater than the calculated theoretical amount. 



Influence of Screens. 



A number of series of experiments and observations were 

 made in the usual manner for the purpose of detecting, if 

 possible, an influence of screens. Each series with a single pair 

 of bars and a single pair of screens extended over five days. 

 The bars included copper, bismuth, lead, and zinc ; and the 

 screens comprised copper, lead, zinc, and tinned iron ; the bars 

 Were of the usual dimensions; the screens were 22 inches : 

 long and 2 inches wide, and the thicknesses of them were : — 

 copper *013 inch, lead *009 inch, zinc *010 inch, and tinned iron 

 •006 inch. The nearest surfaces of them were at a distance- 

 of 3% inch from the axis of the electrodes, and the bars were 

 in immediate contact with them. Copper bars were used' 

 with screens of lead, zinc, and tinned iron ; lead ones with" 

 copper, zinc, and tinned iron ; bismuth with copper, lead,' 

 zinc, and tinned iron ; and zinc with those of lead : no 

 screening effect was detected in any of the eleven instances;' 

 As the radiant influence was not manifestly intercepted by 

 screens, it appears to partake so far of the nature of gravity. 



I have to express thanks to Messrs. Stock & Taylor, 

 of Birmingham, for the loan of 74 cwt. of lead ; to Messrs. 

 Osier for the preparation and loan of bars of glass, brass, and 

 plaster; and to the Magnesium Company, Patricroft, Man- 

 chester, for preparing and lending the bars of magnesium, 

 bismuth, and antimony. 



