234 Contributions to Electricity and Magnetism. 



foot in diameter, the intensity of magnetism appeared to be some- 

 what diminished, if the extra quantity was on the negative side ; 

 and this might be expected, since the free electricity, in its escape 

 to the earth through the riband, in this case would tend to induce 

 a feeble current in the opposite direction to that of the jar. 



106. The spark from an insulated conductor may be considered 

 as consisting almost entirely of this free or extra electricity, and 

 it was found that this was also capable of producing an induced 

 current, precisely the same as that from the jar. In the experi- 

 ment which gave this result, one end of the outer riband of the 

 cylinder (100) was connected with the earth, and the other caused 

 to receive a spark from a conductor fourteen feet long, and nearly 

 a foot in diameter. The direction of the induced current was 

 the same as that of the spark from the conductor. 



107. From these experiments it appears evident that the dis- 

 charge from the Leyden jar possesses the property of inducing a 

 secondary current precisely the same as the galvanic apparatus, 

 and also that this induction is only so far connected with the 

 phenomenon of the lateral discharge as this latter partakes of the 

 nature of an ordinary electrical current, 



108. Experiments were next made in reference to the produc- 

 tion of currents of the different orders by ordinary electricity. 

 For this purpose a second cylinder was prepared with ribands of 

 tinfoil, in a similar manner to the one before described. The 

 two were then so connected that the secondary current from the 

 first would circulate around the second. When a discharge 

 was passed through the outer riband of the first cylinder, a ter- 

 tiary current was induced in the inner riband of the second. 

 This was rendered manifest by the magnetizing of a needle in a 

 spiral, joining the ends of the last mentioned riband. 



109. Also by the addition, in the same way, of a third cylin- 

 der, a current of the fourth order was developed. The same 

 result was likewise obtained by using the arrangement of the 

 coils and helices shown in Fig. 9. For these experiments, how- 

 ever, the coils were furnished 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 between the conductors of different orders. Figures 8 and 9. 

 The precaution was taken to place the metal between two plates 



