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



ferior to copper in cutting off the inductric influence of a con- 

 ductor; and this difference is perceptible with either the first 

 or second induced current; also the difference of magnetizing 

 power between the first and second induced current still re- 

 mains. 



Having reversed the plates, that is, having placed the cop- 

 per where the lead was, and the lead where the copper was, 

 other circumstances being the same as before, the magnetism 

 of the indicating needle announced a current of electricity the 

 reverse of that obtained when the plates were in their former 

 position. In this, and generally in all the following experi- 

 ments, the mercury was not employed to complete the battery 

 circuit, which was effected by bringing together two copper 

 wires ; I have found the results identical with either method. 



A plate of tin ^th of an inch thick and the usual size of 

 4*5 inches square, was placed between A and B, and the similar 

 plate of copper between B and C ; no effect was produced on 

 the needle by completing the battery circuit twelve times ; but 

 when the circuit was closed and opened by drawing one of the 

 terminal wires a few times over a file, the eye end of the needle 

 became as the marked end of a magnet. 



On placing the copper plate between A and B, and the tin 

 plate between B and C, and interrupting the battery current 

 as before, the point of the needle became as the marked end 

 of a magnet. Hence tin acts with regard to copper as lead 

 does, but the difference between tin and copper is less than 

 between lead and copper. 



I now placed between A and B a plate of zinc ~th of an 

 inch thick, and between B and C the similar plate of copper; 

 but although I employed the file I could obtain no magnetism, 

 even when another similar copper plate was laid on that pre- 

 viously used. 



It occurred to me that perhaps such thick plates of metal 

 were unsuited to develope the effects sought ; for denoting by 

 P, P' those portions of the magnetic force which found their 



p 

 way respectively to A and C, then, although p might be very 



great and go on increasing with the thickness of the metal 

 plates, yet P— P', which must be the magnetizing force, might 

 be very small and capable of increase by a somewhat dimi- 

 nished thickness of the plates. This proved to be true. 



I placed between A and B a plate of zinc -j^ydth of an inch 

 thick, and between B and C a plate of copper ^th of an inch 

 thick ; the battery circuit was closed and opened ten times, 

 when the eye end of the indicating needle was its marked mag- 

 netic end. I now reversed the order of the plates, and closed 



