236 Contributions to Electricity and Magnetism. 



instead of affording any new light, seemed to render the obscu- 

 rity 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 experi- 

 ments 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 ; the coils 

 in alternate directions. 



115. After various hypotheses had been formed, and in succes- 

 sion 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 distance between the ribands was 

 nearly one inch and a half, while in the latter it was only the 

 thickness of the glass, or about g'^th of an inch. 



116. In order to put this supposition to the test of experiment, 

 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 ^'^th of an inch. When a discharge from the 

 half gallon jar was passed through one of these, an induced cur- 

 rent in the same direction was obtained from the other. The 

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

 ^'flth of an inch ; 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 diffe?'ent direction, or to be minus. No other change 

 was observed in the direction of the current with a farther in- 

 crease of distance ; the intensity of the induction gradually dimin- 

 ished as the ribands were separated. The existence and direction 

 of the current, in this experiment, were determined by the polar- 

 ity of the needle in the spiral attached to the ends of one of the 

 ribands. 



117. The question at this time arose, whether the direction of 

 the current, as indicated by the polarity of the needle, was the 



* 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 distance. 



