in a Letter to M. Gay-Lussac. 357 



until it reaches the shortest distance, or a little beyond, on 

 account of time entering as an element into this effect. After- 

 wards, by reason of the increasing distance, the current di- 

 minishes in intensity without ever altering its direction rela- 

 tively to its proper course. It is only when it arrives at the 

 parts most distant, at which the electricity excited is dis- 

 charged, that a current is manifested in an opposite direction, 

 or in one more or less oblique. I apprehend that it is wholly 

 useless to speak of the partial alterations in the direction of 

 the currents through the parts that are the nearest to the 

 centre, or to the circumference; two or three curves that I 

 have rudely traced will show in what directions these altera- 

 tions take place. 



The second consequence arising from the memoir of the 

 Italian philosophers is, that " the direction of the currents 

 upon the parts that enter is contrary to that of the producing 

 currents; (that is, of those that are considered as existing in 

 the magnet) while on the other side the direction in the 

 two systems is identical." This assertion is exactly contrary 

 to the reality (F. 117.). In figures 1. and 2. I have indicated, 

 by means of arrows, the direction of the currents in the mag- 

 netic pole, which is the same as the direction given by Messrs. 

 Nobili and Antenori in fig. J. pi. iii. But my figure 2, as 

 well as the indications of the galvanometer, shows evidently 

 that the currents in the parts that enter w, w, n, when they 

 approach the magnet, pass through in the same direction as 

 the current in this side of the pole of the magnet ; and that 

 the currents in the parts that recede s, s, s, follow a direc- 

 tion contrary to those supposed to exist in the side of the 

 magnetic pole from which they recede. 



I may be mistaken, but it appears to me that Messrs. Nobili 

 and Antenori suppose that circular currents are excited in 

 the part of the metal adjacent to the pole, in absolutely the 

 same manner as those formed in the helix, when it is made to 

 approach the magnet, and that when this part of the disc re- 

 cedes, the circular currents are somehow reversed, as occurs 

 in the helix during its recession from the magnet. A passage 

 in their first paper, and another at the end of page 284, ap- 

 pear to imply that such is their opinion. This idea occurred 

 to me above a year ago, but I soon saw from numerous ex- 

 periments, some of which I have just referred to, that it was 

 by no means satisfactory ; and when I had fully verified that 

 the action of the helix in its approach to, and recession 

 from the pole was wholly explained (F. 42.) by the law as- 

 signed (F. 1 14.), I was forced to abandon my previous ideas. 



The memoir afterwards proceeds (p. 288.) to explain the 



