238 Contributions to Electricity and Magnetism. 
121. The most important experiments, in reference to distance, 
were made in the Jecture room of my respected friend Dr. Hare 
of Philadelphia, with the splendid electrical apparatus described 
in the Fifth Volume (new series,) of the ‘Transactions of this 
Society. The battery consists of thirty-two jars, each of the 
capacity of a gallon. A thick copper wire of about ;;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 
fect. Along this side a wire was stretched of the ordinary bell 
size, and the extreme ends of Fig. 13. 
this joined by a spiral, similar to ec 
the arrangement shown in Fig. 
13.. The two wires were at 
first placed within the distance 
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 de- 
veloped in a needle in the spiral 
at 6, but when the circuit was 
complete, the needle at each dis- © -— oe am 
charge indicated a currentin the — Place of the battery, ? sp _ 
same direction as that of the battery. When the distance of the 
two wires was inereased to sixteen inches, and the ends of the 
second wire placed in two glasses of mercury, and a finger of 
each hand plunged into the metal, a shock was received. The 
direction of the current was still the same, but the magnetism 
not as strong as at a less distance. 
122. "The second wire was next arranged around the other, 5° 
as to enclose it. The magnetism by this arrangement appeare 
stronger than with the last; the direction of the current was 
still the same, and continued thus, until the two wires were at 
every point separated to the diktnee of twelve feet, except in 
one place where they were obliged to be crossed at the distance 
of seven feet, but here the wires were made to form a right angi? 
with each other, and the effect of the approximation was there 
fore (46) considered as nothing. The needle at this surprising 
