560 Prof. J. Henry's Contribuiiofis 



galvanism, as well as from electricity, first produces an in- 

 ductive action in the direction of itself, and that the inverse 

 influence takes place at a little distance from the wire. 



128. To test this, the compound helix was placed on coil 

 No. 1, to receive the induction, and its ends joined to those 

 of the outer riband of tinfoil of the glass cylinder, while the 

 magnetizing spiral was attached to the ends of the inner ri- 

 band. A feeble tertiary current was produced by this ar- 

 rangement, which in two cases gave a polarity to the needle 

 indicating a direction the same as that of the primary current. 

 In other cases the magnetism was either imperceptible or 

 minus. With an arrangement of two coils of wires around 

 two glass cylinders, one within the other, the same effect was 

 produced. The magnetism was less when the distance of the 

 two sets of spires was smaller, indicating, as it would appear, 

 an approximation to a position of neutrality. These results 

 are rather of a negative kind, yet they appear to indicate the 

 same change with distance in the case of the galvanic cur- 

 rents, as in that of the discharge of ordinary electricity. The 

 distance however at which the change takes place would seem 

 to be less in the former than in the latter. 



129. There is a perfect analogy between the inductive ac- 

 tion of the primary current from the galvanic apparatus and 

 of that from the larger electrical battery. The point of change, 

 in each, appears to be at a great distance. 



J30. The neutralizing effect described in Section IV. may 

 now be more definitely explained by saying, that when a third 

 conductor is acted on at the same time by a primary and se- 

 condary current (unless it be very near the second wire) it 

 will fall into the region of the plus influence of the former, and 

 into that of the viimis influence of the latter; and hence no 

 induction will be produced. 



131. This will be rendered perfectly clear by fig. 15, in 

 which a represents the con- 

 ductor of the primary cur- S' ^' 



rent, b that of the second- ^ + ^ 



ary, and c the third con- -j-__ -. i-- b 



ductor. The characters + o 



~' c 



-h + +, &c., beginning at + _ 



the middle of the first + — 



conductor and extending ■*"" 



downwards, represent the constant plus influence of the 



primary current, and those -}- , &c., beginning at the 



second conductor, indicate its inductive influence as changing 

 with the distance. The third conductor, as is shown by the 



