380 WRITINGS OF JOSEPH HENRY. [1855- 



this prediction, on the occurrence of the first thunder-storm 

 the apparatus received a discharge from the cloud, which 

 fused several holes in the upper part of the ball and indented 

 the surface, but fortunately did no damage to the building. 

 The apparatus was then removed, and the ball deposited in 

 the museum of the Smithsonian Institution as an interest- 

 ing illustration of the chemical and mechanical effects of a 

 discharge of lightning. 



Effects of telegraph wires. — In 1846, the Hon. S. D. Ingham, 

 of Pennsylvania, requested the opinion of the American 

 Philosophical Society as to whether security in regard to 

 accidents from lightning is increased or lessened by the 

 erection of telegraph wires, the poles of which are placed 

 by the side of the roads along which persons with horses 

 and carriages are constantly passing. The subject was 

 referred to the writer, from whose report in regard to it 

 the following facts and deductions are given. * The wires 

 of a telegraph are liable to be struck by a direct charge 

 from the clouds, and several instances of this kind have be*en 

 observed. About the 20th of May, 1846, the lightning struck 

 the elevated part of the wire which is supported on a high 

 mast where the wire 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 reg- 

 ular intervals down the supporting poles. At each point 

 where the discharge took place along a pole a number of 

 sharp explosions were heard in succession, resembling the 

 rapid reports of several rifles. During another storm the 

 wire was struck in two places on the route between New 

 York and Philadelphia. At one of these places twelve poles 

 were struck and at the other eight. In some instances the 

 lightning has been seen coursing along the wire like a stream 

 of light, and in one case it is described as exploding from 

 the wire in several places, though there were no bodies in 

 the vicinity to attract it from the conductor. 



That the wires of the telegraph should be frequently struck 



* [Proceedings Am. Phil. Society, June 19, 1846, see ante, vol. i, p. 244.] 



