557 
to Electricity and Magnetism* 
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 110 and 114, 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 this respect the 
result is similar to the effect of primary 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 y^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. 
0 
stance of about an inch, and afterwards constantly separated 
after each discharge of the whole battery through the thick 
wire. When a break was made in the second wire at a, no 
magnetism was developed in a needle in the spiral at 5; but 
when the circuit was complete, th^ needle at each discharge 
