342 EECENT PROGRESS IN PHYSICS. | 



insulating substances were interposed between the main and secondary 

 spirals. 



If solid insulators possess a greater specific inductive capacity than 

 air a well marked distinction should be made by means of the secondary 

 current between solid conductors and insulators of electricity. Thus, 

 while conductors, used as interposed plates, diminish the secondary 

 current obtained through the medium of the air, insulators, applied 

 as interposed plates, should increase the current. 



In spite of careful investigation Riess was unable to find such an 

 increase of the secondary current by the interposition of insulating ; 

 plates, such as glass, shellac, &c. The use of these plates changes in no i 

 respect the force of the secondary current, which was found just as i 

 great as though air only had been between the sj)irals. — (Pog. Ann., 

 L, 18.) 



§ 64. Action of the conducting wire of a battery upon itself. — We have ' 

 seen that no electrical current can be generated by induction in a wire • 

 with free ends. The conducting wire of an electrical battery is sucli I 

 a wire, but since its free ends pass into broad metallic surfaces, ^: 

 allowing the accumulation of opposite electricities, it is necessary to 

 examine experimentally whether one part of the wire may not have 

 an inductive action on another part. 



Riess sought to solve this question in the following manner: 

 (Pog. Ann., L, 19.) 



The two spirals, one of which had served hitherto as the main, the 

 other as the secondary spiral, were placed at a short distance apart, ' 

 and joined so as to form a single conducting wire, so that, on being 

 introduced into the circuit of the battery, the discharge current had to 

 pass through both. 



In one case the outer end of one of the spirals was united with the cen- 

 tral end of the other in such a way that when the discharge current in 

 the one spiral passed from the middle to the outside, it had to pass from 

 the middle to the outside in the other also ; and, consequently, the 

 discharge traversed the two spirals in the same direction. 



The outer end of one spiral was then joined to the outer end of the 

 other, so that the current which traversed the one from the middle 

 to the outside went from the outside to the middle in the other ; the 

 discharge thus traversing the two spirals in opposite directions. 



Now, if one part of the conducting circuit can act upon another, ' 

 each spiral in the first case must cause in the other a current in the 

 same direction as the main current, but in the last mode of connecting 

 the spirals a current opposed to the main current ; and hence, in the 

 last case the force of the current, cceteris paribus, should be weaker 

 than in the first. 



The thermometer being introduced into the circuit along with the 

 combined spirals, it indicated, under like circumstances, perfectly 

 equal temperature, in whichever manner the spirals were united ; hence 

 it follows, that in the discharge of a battery no part of the conducting 

 wire acts inductively upon another part. 



§ 65. Retardation of the electrical discharge by conductors near the 

 conducting wire of a battery. — Riess introduced into the conducting 



