On Electro- Dynamic Induction. 237 



true one, since the magnetizing spiral might possibly itself, in 

 some cases, induce an opposite current. To satisfy myself on 

 this point, a series of charges, of various intensity and quantity, 

 from a single spark of the large conductor to the full charge of 

 nine jars, were passed through the small spiral, which had been 

 used in all the experiments ; but they all gave the same polarity. 

 The interior of this spiral is so small, that the needle is through- 

 out in contact with the wire. 



118. The fact of a change in the direction of the induced cur- 

 rent by a change in the distance of the conductors, being thus 

 established, a great number and variety of experiments were 

 made to determine the other conditions on which the change 

 depends. These were sought for in a variation of the intensity 

 and quantity of the primary discharge, in the length and thick- 

 ness of the wire, and in the form of the circuit. The results 

 were, however, in many cases, anomalous, and are not sufficiently 

 definite to be placed in detail before the Society. I hope to re- 

 sume the investigation at another time, and will therefore at 

 present briefly state only those general facts which appear well 

 established. 



119. With a single half gallon jar, and the conductors sepa- 

 rated to a distance less than -^\\h of an inch, the induced current 

 is always in the same direction as the primary. But when the 

 conductors are gradually separated, there is always found a dis- 

 tance at which the current begins to change its direction. This 

 distance depends certainly on the amount of the discharge, and 

 probably on the intensity ; and also on the length and thickness 

 of the conductors. With a battery of eight half gallon jars, and 

 parallel wires of about ten feet long, the change in the direction 

 did not take place at a less distance than from twelve to fifteen 

 inches, and with a still larger battery and longer conductors, no 

 change was found, although the induction was produced at the 

 distance of several feet. 



120. The facts given in the last paragraph relate to the induc- 

 tive action of the primary current ; but it appears from the results 

 detailed in paragraphs 110 and 114, that the currents of all the 

 other orders also change the direction of the inductive influence 

 with a change of the distance. In these cases, however, the 

 change always takes place at a very small distance from the con- 

 ducting wire ; and in this respect the result is similar to the efiect 

 of di primary current from the discharge of a small jar. 



