330 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



114. To discover, if possible, the cause of this difference, a series of 

 experiments was instituted ; but the first fact developed, instead of af- 

 fording any new light, seemed to render the obscurity more profound. 

 When the directions of the currents were taken in the arrangement of 

 the coils (Fig. 9) the discrepancy vanished. Alternations were found 

 the same as in the case of galvanism. This result was so extraordinary 

 that the experiments were many times repeated, first with the glass 

 cylinders, and then with the coils ; the results, however, were always 

 the same. The cylinders gave currents all in one direction j the coils 

 in alternate directions. 



115. After various hypotheses had been formed, and in succession 

 disproved by experiment, the idea occurred to me that the direction of 

 the currents might depend on the distance of the conductors, and this 

 appeared to be the only difference existing in the arrangement of the 

 experiments with the coils and the cylinders.* In the former the dis- 

 tance between the ribands was nearly one inch and a half, while in 

 the latter it was only the thickness of the glass, or about Toth of an 

 inch. 



116. In order to test this idea, two narrow slips of tinfoil, about 

 twelve feet long, were stretched parallel to each other, and separated 

 by thin plates of mica to the distance of about rVth of an inch. When 

 a discharge from the half gallon jar was passed through one of these, 

 an induced current in the same direction was obtained from the other. 

 The ribands were then separated, by plates of glass, to the distance of 

 aVth of an inch j the current was still in the same direction, or plus. 

 When the distance was increased to about |th of an inch, no induced 

 current could be obtained ; and when they were still further separated 

 the current again appeared, but was now found to have a different di- 

 rection, or to he minus. No other change was observed in the direc- 

 tion of the current ; the intensity of the induction decreased as the 

 ribands were separated. The existence and direction of the current, in 

 this experiment, were determined by the polarity of the needle in the 

 spiral attached to the ends of one of the ribands. 



* This idea was not immediately adopted, because I had previously experimented on the 

 direction of the secondary current from galvanism, and found no change in reference to dis- 

 tance. 



