370 Mr. J. J. Waterston on some Electrical Experiments. 



Had the Messrs. Siemens followed this plan, then the use of 

 the wrong specific gravity would not so much influence the 

 value of their coils as means of comparison, as the differences 

 in the values of the coils themselves ; for when we find a Siemens 

 unit used, we must first discover what value it has, because, as 

 already pointed out, the different issues have different values. 



LII. On some Electrical Experiments. 

 By J. J. Waterston, Esq. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN § 30 of the paper on Electric Experiments, T have in- 

 advertently stated that the leaves of the electroscope diverged 

 with negative electricity, instead of positive. The experiment 

 was meant to direct attention to a simple mode of proving, by 

 means of a Leyden jar and electroscope, that the force of electric 

 induction is capable of acting in curved lines, a fact which appears 

 to deserve that distinct announcement due to a fundamental 

 characteristic of the electric force. 



Suppose we take a coated plate of glass properly insulated, and 

 charge it highly with positive electricity on the side A, and ne- 

 gative on the opposite side B. After leaving it in this charged 

 state for a few seconds, let an electroscope be brought with its 

 cap near the centre of A, but not touching it : the leaves are found 

 to diverge with positive in consequence of the free positive on 

 the outer side of coating A acting inductively on the cap of elec- 

 troscope, exciting upon it negative, and on the gold-leaves a cor- 

 responding amount of positive. In the same way, if we remove 

 the electroscope from near A and place it on the opposite side close 

 to centre of B, the leaves will diverge with negative from the 

 action of the free negative on the outer side of B. 



While the electroscope is thus stationed close to B, let A be 

 touched: the leaves increase their divergence, showing that the 

 free negative on the outer side of B has received an augmenta- 

 tion. The electroscope is then to be immediately removed to 

 the opposite side, and the cap made to touch the centre of coat- 

 ing A. The leaves do not open, there is no longer electric 

 excitement on the outer side of A : it has been discharged by 

 touching. If we gradually remove the electroscope further away 

 from the plate, but still keep it opposite the centre of A, the 

 leaves diverge with negative more and more until a certain maxi- 

 mum is attained, after which they gradually sink as the distance 

 is further increased. The inductive action cannot come from 

 an> part of the adjacent coating A, which is altogether positive; it 



