Prof. Henry on Electrical Induction, §c. 25 
Art. I.—On the Induction of Atmospheric Electricity on the 
Wires of the Electrical Telegraph ; by Prof. Joseru Henry.* 
Tue action of the electricity of the atmosphere on the wires of 
the electrical telegraph, is at the present time a subject of much 
importance, both on account of its practical bearing, and the 
number of purely scientific questions which it involves. I have 
accordingly given due attention to the letter referred to me, and 
have succeeded in collecting a number of facts in reference to 
the action in question. Some of these are from the observations 
of different persons along the principal lines, and others from my 
own investigations during a thunder-storm on the 19th of June, 
when I was so fortunate as to be present in the office of the tel- 
egraph in Philadelphia, while a series of very interesting electri- 
-eal phenomena was exhibited. In connexion with the facts de- 
rived from these sources, I must ask the indulgence of the society 
in frequently referring, in the course of this communication, to 
the results of my previous investigations in dynamic electricity, 
accounts of which are to be found in the Proceedings and 'Trans- 
actions of this Institution. 
the 20th of May, the lightning struck the clevated part of the 
wire, which is supported on a high mast at the place where the 
telegraph crosses the Hackensack river. The fluid passed along 
the wire each way, from the point which received the discharge, 
for several miles, striking off at irregular intervals down the sup- 
porting poles. At each place where the discharge to a pole took - 
place, a number of sharp explosions were heard in succession, re- 
sembling the rapid reports of several rifles. « During another 
storm, the wire was struck in two places in Pennsylvania, on the 
pole escaped the discharge; and the same phenomenon was s 
served, though in a less marked degree, near the Hackensac 
river. In some instances the lightning has been seen coursing 
along the wire in a stream of light; and in another case 1t 1s ce- 
scribed as exploding from the wire at certain points, though 
“Ves Hap peds ee Be ao 
* Communieated by the author from the Proceedings of the American Philo: 
sophical Society, vol iv, p. 260.000 
rconp Srrizs, Vol. ili, No, 7.—Jan., 1847. ‘ 
