1838] WRITINGS OP JOSEPH HENRY. 137 



remarkable difference in the action of the two. I allude to 

 the direction of the currents of the different orders. These, 

 in the experiments with the glass cylinders, instead of ex- 

 hibiting the alternations of the galvanic currents (92), were 

 all in the same direction as the discharge from the jar, or 

 in other words, they were all plus. 



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

 a series of experiments was instituted ; but the first fact de- 

 veloped, instead of affording any new light, seemed to ren- 

 der 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 how- 

 ever 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 

 succession disproved by experiment, the idea occurred to me 

 that the direction of the currents might depend on the dis- 

 tance 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 ribbons was nearly one inch and a half, while 

 in the latter it was only the thickness of the glass, or about 

 ■j^^th 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 

 -g^th 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 ribbons 

 were then separated, by plates of glass, to the distance of ^V^h 

 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 



*This idea was not immediately adopted, because I had previously experi- 

 mented on the direction of the secondary current from galvanism, and found 

 no change in reference to distance. 



