to Electricity and Magnetism. 557 



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 in- 

 ductive action of the primary current; but it appears from 

 the results detailed in paragraphs IJO and IH, that the cur- 

 rents 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 conducting wire; and in diis respect the 

 result is similar to the effect of a jirimart/ current from the dis- 

 charge of a small jar. 



121. The most important experiments, in reference to di- 

 stance, were made in the lecture-room of my respected friend 

 Dr. Hare of Philadelphia, with the splendid electrical appa- 

 ratus described in the fifth volume (new series) of the Trans- 

 actions of this Society. The battery consists of thirty-two 

 jars, each of the capacity of a gallon. A thick copper wire 

 of about J^th of an inch in diameter and eighty feet in length, 

 was stretched across the lecture-room, and its ends brought 

 to the battery, so as to form a trapezium, the longer side of 

 which was about thirty-five feet. Along this side a wire was 

 stretched of the ordinary bell size, and the extreme ends of 

 this joined by a spiral, similar to the arrangement shown in 

 fig. 13. The two wires were at first placed within the di- 



Fig. 13. 



\ 

 J. 



\ 



b 

 c place of the battery, h spiral, 

 stance of about an inch, and afterwards constandy separated 

 after each discharge of the whole battery through the thick 

 wire. When a break was made in the second wire at ^, no 

 magnetism was developed in a needle in the spiral at h\ but 

 when the circuit was complete, the needle at each discharge 



