1838] WRITINGS OF JOSEPH HENRY. 135 



peared to be somewhat 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 ribbon, 

 in this case would tend to induce a feeble current in the op- 

 posite direction to that of the jar. 



106. The spark from an insulated conductor may be con- 

 sidered 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 experiment which gave this result, 

 one end of the outer ribbon of the cylinder (100) was con- 

 nected 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 

 discharge from the Leyden jar possesses the property of in- 

 ducing a secondary current precisely the same as the gal- 

 vanic 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 pro- 

 duction of currents of the different orders by ordinary elec- 

 tricity. For this purpose a second cylinder was prepared 

 with ribbons of tinfoil, in a similar manner to the one before 

 described. The two were then so connected that the second- 

 ary current from the first would circulate around the second. 

 When a discharge was passed through the outer ribbon of 

 the first cylinder, a tertiary current was induced in the inner 

 ribbon of the second. This was rendered manifest by the 

 magnetizing of a needle in a spiral joining the ends of the 

 last mentioned ribbon. 



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

 cylinder, 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 experi- 

 ments however the coils were furnished with a double coat- 



