158 WRITINGS OP JOSEPH HENRY. [1840 



induction. In short, the series of induced currents produced 

 at the beginning of the primary current appeared to possess 

 all the properties belonging to those of the induction at the 

 ending of the same current. 



23. I may mention in this place that I have found in the 

 course of these experiments that the neutralizing power of a 

 plate of metal depends in some measure on its superficial 

 extent. Thus a broad plate which extends in every direc- 

 tion beyond the helix and coil, produces a more perfect 

 screening than one of the same metal and of the same thick- 

 ness, but of a diameter only a little greater than that of the 

 coil. 



24. The next step in the investigation was to determine 

 the direction of the currents of the different orders produced 

 by the beginning induction; and for this purpose the mag- 

 netizing spirals (5) were used, and the results obtained by 

 these verified by the indications of the galvanometer. It 

 should be stated here, as a fact which was afterwards found 

 of some importance, that although the needle of the galva- 

 nometer was powerfully deflected when the instrument was 

 placed in the circuit of the secondary current, yet a ver}' 

 feeble effect was produced on it by the action of a current 

 of the third, fourth, or fifth order. The directions however 

 of these currents, as indicated by the feeble motions of the 

 needle, were the same as those given by the magnetizing 

 spiral. 



25. The direction of the different currents produced at the 

 making of the battery current, as determined by these in- 

 struments, is as follows, namely: the direction of the sec- 

 ondary current is, as stated by Dr. Faraday, adverse to that 

 of the primary current, and also the direction of each suc- 

 ceeding current is opposite to that of the one which produced 

 it. We have therefore from these results, and those formerly 

 obtained, (No. Ill, 92,) the following series of directions of 

 currents, one produced at the moment of beginning, and the 

 other at that of ending of the battery current. 



