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On Electro-Dynamic Induction. 235 
of glass, in order to be assured that the effect was not due to a 
want of perfect insulation. “oigs 
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 sep- 
arated, 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. 
Fig. 12. 
a coil No. 2, } an inverted bell glass, ¢ helices No, 2 and 3. 
112. Likewise shocks were obtained from the secondary cur- 
rent by an arrangement shown in Fig. 12. Helices No. 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 intensity 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 investi- 
gation there appeared what at first was considered a remarkable 
difference in the action of the two. T allude to the direction of 
the currents of the different 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. 
114. To discover, if possible, the cause of this difference, a 
Series of experiments was instituted ; but the first fact developed, 
