30 Prof. Henry on Electrical Induction 
the case. Sparks were seen at the breaks in the continuity of 
the rail, with every flash of a distant thunder-cloud. 
Similar effects, but in a greater degree, must be produced on 
the wire of the telegraph, by every discharge in the heavens; 
and the phenomena which I witnessed on the 19th of June in 
storm at Washington, and another at Jersey City. The portion 
of the circuit of the telegraph which entered the building, and 
was connected with one pole of the galvanic battery, happened 
to pass within the distance of less than an inch of the wire 
which served to form the connexion of the other pole with the 
earth. Across this space, at an interval of every few minutes, a 
series of sparks in rapid succession was observed to pass; an 
when one of the storms arrived so near Philadelphia that the 
lightning could be seen, each series of sparks was found to be 
simultaneous with a flash in the heavens. Now we cannot sup- 
se, for a moment, that the wire was actually struck at the time 
each flash took place ; and indeed it was observed that the sparks 
were produced when the cloud and flash were at the distance of 
several miles to the east of the line of the wire. The inevitable | 
conclusion is, that all the exhibition of electrical phenomena wit- 
nessed during the afternoon, was purely the effect of induction, 
or the mere disturbance of the natural electricity of the wire at a 
distance, without any transfer of the fluid from the cloud to the 
us. . i bas 
_ The discharge between the two portions of the wire continued 
for more than an hour, when the effect became so powerful, that 
the superintendent, alarmed for the safety of the building, con- 
nected the long wire with the city gas pipes, and thus transmitted 
the current silently to the ground. I was surprised at the quan- 
tity and intensity of the current; it is well known, that to affect 
a common galvanometer with ordinary electricity, requires the 
discharge of a large battery ; but such was the quantity of the 
induced current exhibited on this occasion, that the needle of an 
ordinary vertical galvanometer, with a short wire, and apparently 
of little sensibility, was moved several degrees. 
The pungency of the spark was also, as might have been ex- 
pected, very great. When a small. break was made in the cir- 
uit, and the parts joined by the fore-finger and thumb, the dis- 
charge transmitted through the hand affected the whole arm up 
to the shoulder. I was informed by the superintendent, that on 
another ¢casion a spark passed over the surface of the spool of 
wire, surrounding the legs of the horse-shoe magnet at right an- 
