1840] WRITINGS OF JOSEPH HENRY. 151 



article is formed of a long, fine wire, making about one 

 hundred turns around the axis of a hollow piece of straw 

 about two inches and a half long: also the spiral mentioned 

 in connection with a coil, is formed of a short wire which 

 makes about twenty turns around a similar piece of straw. 

 The reason of the use of the two instruments in these two 

 cases is the same as that for the galvanometers, under sim- 

 ilar circumstances, namely, the helix gives a current of in- 

 tensity, but of small quantity, while the coil produces one of 

 considerable quantity, but of feeble intensity. 



SECTION I. 



On the Induction produced at the moment of the Beginning oj a 

 Galvanic Current, Sec. 



6. It will be recollected that the arrangement of appara- 

 tus employed in my last series of experiments gave a power- 

 ful induction at the moment of breaking the galvanic cir- 

 cuit, but the effect at making the same was so feeble as 

 scarcely to be perceptible. I was unable in any case to get 

 indications of currents of the third or fourth orders from the 

 beginning induction, and its action was therefore supposed 

 to be so feeble as not materially to affect the results obtained. 



7. Subsequent reflection however led me to conclude that 

 in order to complete this part of my investigations, a more 

 careful study of the induction at the beginning of the cur- 

 rent would be desirable; and accordingly on resuming the 

 experiments, my attention was first directed to the discovery 

 of some means by which the intensity of this induction 

 might be increased. After some preliminary experiments, 

 it appeared probable that the desired result could be ob- 

 tained by using a compound galvanic batter}^ instead of the 

 single one before employed. In reference to this conjecture, 

 the constant battery before mentioned (3) was constructed, 

 and a series of experiments instituted with it, the results of 

 which agreed with my anticipation. 



8. In the first experiment, coil No. 2, which it will be re- 

 membered (No. Ill, 7,) consists of a copper ribbon about sixty 

 feet long, coiled on itself like the main spring of a watch, 



