ON ELECTRO-DYNAMIC INDUCTION. 329 



With a double coating of silk, and the contiguous conductors separated 

 by a large plate of glass. 



110. Screening effects precisely the same as those exhibited in the 

 action of galvanism were produced by interposing a plate of metal be- 

 tween the conductors of different orders, Figures 8 and 9. The pre- 

 caution was taken to place the plate between two frames of glass, in 

 order to be assured that the effect was not due to a want of perfect in- 

 sulation. 



111. Also analogous results were found when the experiments were 

 made with coils interposed instead of plates, as described in paragraph 

 68. When the ends of the interposed coils were separated, no screen- 

 ing was observed, but when joined, the effect was produced. The 

 existence of the induced current, in all these experiments, was deter- 

 mined by the magnetism of a needle in a spiral attached to one of the 

 coils. 



112. Likewise shocks were obtained from the secondary current by 



p. an arrangement shown in Fig. 12. 



----- <s=5 Helices No. 2 and No. 3 united are put 



/^^"^^ within a glass jar, and coil No. 2 is 



{/" '^ placed around the same. When the 



'^^^~^=^::ajsiK ^^^^^^ handles are grasped, a shock is felt at 



*^^~^-^^=="^^^^^^^P "■ the moment of the discharge, through 



- liiZ!3 the outer coil. The shocks, however, 



** were very different in intensity with 



a coil No. 2, 6 an inverted bell glass, *' •' 



c helices No. 2 and 3. different discharges from the jar. In 



some cases no shock was received, when again, with a less charge, a 

 severe one was obtained. But these irregularities find an explanation 

 in a subsequent part of the investigation. 



113. In all these experiments, the results with ordinary and galvanic 

 electricity are similar. But at this stage of the investigation there ap- 

 peared what at first was considered a remarkable difference in the ac- 

 tion of the two. I allude to the direction of the currents of the dif- 

 ferent orders. These, in the experiments with the glass cylinders, 

 instead of exhibiting 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. 



