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struck by lightning, which exhibited some effects of an interesting 

 kind. The lightning struck the top of the chimney, passed down the 

 interior of the flue to a point opposite a mass of iron placed on the 

 floor of the garret, where it pierced the chimney ; thence it passed 

 explosively, breaking the, plaster, into a bedroom below, where it 

 came in contact with a copper bell-wire, and passed along this hori- 

 zontally and silently for about six feet; thence it leaped explosively 

 through the air a distance of about ten feet, through a dormer win- 

 dow, breaking the sash, and scattering the fragments across the 

 street. It was evidently attracted to this point by the upper end of a 

 perpendicular gutter, which was near the window. It passed silently 

 down the gutter, exhibiting scarcely any mark of its passage until it 

 arrived at the termination, about a foot from the ground. Here again 

 an explosion appeared to have taken place, since the windows of the 

 cellar were broken. A bed, in which a man was sleeping at the 

 time, was situated against the wall, immediately under the bell- wire ; 

 and although his body was parallel to the wire, and not distant from 

 it more than four feet, he was not only uninjured, but not sensibly 

 affected. The size of the hole in the chimney, and the fact that the 

 lightning passed along the copper wire without melting it, show that 

 the discharge was a small one, and yet the mechanical effects, in 

 breaking the plaster, and projecting the window frame across the 

 street, were astonishingly great. 



These effects the Professor attributes to a sudden repulsive energy, 

 or expansive force developed in the air along the path of the dis- 

 charge. Indeed, he conceives that most of the mechanical effects 

 which are often witnessed in cases of buildings struck by lightning, 

 may be referred to the same cause. In the case of a house struck 

 within a few miles of Princeton, the discharge entered the chimney, 

 burst open the flue, and passed along the cockloft to the other end of 

 the house ; and such was the explosive force in this confined space, 

 that nearly the whole roof was blown off. This effect was, in all 

 probability, due to the same cause which suddenly expands the air in 

 the experiment with Kinnersly's electrical air thermometer. 



Dr. Patterson stated, that Mr. Jefferson was of the opinion 

 that metal roofs protected buildings, not from being struck, but 

 from the danger of the stroke; the contrary opinion is gene- 

 rally held, but Prof. Henry's experiments show that Mr. Jef- 

 ferson was correct. Dr. P. saw the lightning strike a row of 

 dormitories with metal roofs, at the University of Virginia; 



