Mr. R. Phillips on Volta- Electric Induction. 267 



In concluding I cannot but observe, that the power pos- 

 sessed by the different metals I have yet employed to shut off 

 the circumferential influence of an electric current varies as 

 their electric conduction ; for we have them in the order of 

 copper, zinc, tin and lead, which is that of their relative powers 

 of electric conduction according to Harris. This view is further 

 confirmed by the difference produced by thick and thin plates 

 of the same metal. Indeed the following experiment clearly 

 shows that the office of a metal, in thus intercepting volta- 

 electric induction, is that of an electric conductor. 



The former arrangement of A, B and C was restored ; and 

 of two similar plates of zinc, each T ^dth of an inch thick, one 

 was placed between A and B and the other between B and C ; 

 then by the aid of a file I rapidly made and broke the battery 

 current through B, but could obtain no magnetism in the in- 

 dicating needle. I now removed the plate from between B 

 and C, and commencing at the middle point of one of its edges, 

 I cut a slit at a right angle to the edge 3'5 inches long and -1 

 of an inch wide ; the plate was then replaced in its former 

 position between B and C, and the battery closed and opened 

 once through B, which made the point of the indicating needle 

 as the marked end of a magnet. When the position of the 

 plates was reversed, the magnetism of the indicator was also 

 reversed. Therefore a plate is to its fellow which has been 

 slit as copper is to lead ; and, moreover, the only assignable 

 use of the slit is to prevent the circulation of electric currents. 



With regard to constructing the three coils with which these 

 foregoing results are to be obtained, I would remark they 

 should not be much more than half an inch thick each ; they 

 may however contain any quantity of wire, and be of any dia- 

 meter consistently with the power of the battery. I propose 

 to call this instrument a differential volta-inductometer. 



By means of my three small coils it is easy to obtain a shock 

 from the specific induction of a metal, by removing the indi- 

 cator from the ends of the coils A and C, these coils being of 

 course set so as to tend to circulate the induced current in 

 opposite directions through each other; then having placed a 

 plate of copper next B and brought the unattached ends of A 

 and C to one's tongue, on closing and opening the battery 

 circuit through B the shock is obtained. 



7 Prospect Place, Ball's Pond Road, 

 August 8, 1848. 



T2 



