ON ELECTRO-DYNAMIC INDUCTION. 9 



ginning 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 

 direction, beyond the helix and coil, produces a more perfect screening than 

 one of the same metal and of the same thickness, 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 magnetizing 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 afterward found of some importance, that although 

 the needle of the galvanometer was powerfully deflected when the instrument 

 was placed in the circuit of the secondary current, yet a very 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 motion 

 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 instruments, is as follows, namely : 

 the direction of the secondary current is, as stated by Dr. Faraday, adverse to 

 that of the primary current, and, also, the direction of each succeeding current 

 is opposite to that of the one which produced it. We have, therefore, from 

 these results, and those formerly obtained, (III. 92,) the following series of di- 

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

 at that of ending of the battery current. 



Primary current, .... 

 Secondary current, . . . 

 Current of the third order, . 



At the Beginning. 



+ . . 



At the Ending 

 • • + 



Current of the fourth order, 





. . + 



Current of the fifth order, . 



+ . . 







26. These two series, at first sight, may appear very different, but, with a 

 little attention, they will be seen to be of the same nature. If we allow that 



VIII. — c 



