276 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XIV.) 



between the magnet and these helices (1713.), produced not the least effect, whether 

 the former were quiescent or in rapid revolution (1715.). So here no evidence of the 

 influence of the intermediate particles could be obtained (171O.). 



1720. The magnet was then removed and replaced by a flat helix, corresponding 

 to the two former, the three being parallel to each other. The middle helix was so 

 arranged that a voltaic current could be sent through it at pleasure. The former 

 galvanometer was removed, and one with a double coil employed, one of the lateral 

 helices being connected with one coil, and the other helix with the other coil, in such 

 manner that when a voltaic current was sent through the middle helix its inductive 

 action (26.) on the lateral helices should cause currents in them, having contrary 

 directions in the coils of the galvanometer. By a little adjustment of the distances 

 these induced currents were rendered exactly equal, and the galvanometer needle 

 remained stationary notwithstanding their frequent production in the instrument. I 

 will call the middle coil C, and the external coils A and B. 



1721. A plate of copper 0*7 of an inch thick and six inches square, was placed be- 

 tween coils C and B, their respective distances remaining unchanged ; and then a 

 voltaic current from twenty pairs of 4-inch plates was sent through the coil C, and in- 

 termitted, in periods fitted to produce an effect on the galvanometer (1712.), if any 

 difference had been produced in the effect of C on A and B. But notwithstanding 

 the presence of air in one interval and copper in the other, the inductive effect was 

 exactly alike on the two coils, and as if air had occupied both intervals. So that 

 notwithstanding the facility with which any induced currents might form in the 

 thick copper plate, the coil outside of it was just as much affected by the central helix 

 C as if no such conductor as the copper had been there. 



] 722. Then, for the copper plate was substituted one of sulphur 0*9 of an inch thick ; 

 still the results were exactly the same, i. e. there was no action at the galvanometer. 



1723. Thus it appears that when a voltaic current in one wire is exerting its induc- 

 tive action to produce a contrary or a similar current in a neighbouring wire, accord- 

 ing as the primary current is commencing or ceasing, it makes not the least difference 

 whether the intervening space is occupied by such insulating bodies as air, sulphur and 

 shell- lac, or such conducting bodies as copper, and the other non-magnetic metals. 



1724. A correspondent effect was obtained with the like forces when resident in a 

 magnet thus. A single flat helix (1718.) was connected with a galvanometer, and a ma- 

 gnetic pole placed near to it ; then by moving the magnet to and from the helix, or the 

 helix to and from the magnet, currents were produced indicated by the galvanometer. 



1725. The thick copper plate (1721.) was afterwards interposed between the ma- 

 gnetic pole and the helix ; nevertheless on moving these to and fro, effects, exactly 

 the same in direction and amount, were obtained as if the copper had not been there. 

 So also on introducing a plate of sulphur into the interval, not the least influence on 

 the currents produced by motion of the magnet or coils could be obtained. 



1726. These results, with many others which I have not thought it needful to de- 



