136 WRITINGS OP JOSEPH HENRY. [1838 



ing 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 between the conductors of different orders. 

 Figures 8 and 9. The precaution 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 insulation. 



111. Also analogous results were found when the experi- 

 ments were made with coils interposed instead of plates, as 

 described in paragraph 68. When the ends of the inter- 

 posed coils were separated, no screening was observed, but 

 when joined, the effect was produced. The existence of the 

 induced current, in all these experiments, was determined 

 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 an arrangement shown in Fig. 12. Helices No. 



'h 



Fig. 12. — a coil No. 2, b an inverted bell glass, c helices No. 2 and 3. 



2 and No. 3 united are put within a glass jar, and coil No. 2 

 is placed around the same. When the handles are grasped, 

 a shock is felt at the moment of the discharge, through the 

 outer coil. The shocks however were very different in in- 

 tensity with 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 appeared what at first was considered a 



