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Professor Henry also made a communication relative to a 

 simple method of protecting from lightning, buildings covered 

 with metallic roofs. 



On the principle of electrical induction, houses thus covered are 

 evidently more liable to be struck than those furnished either with 

 shingle or tile. Fortunately, however, they admit of very simple 

 means of perfect protection. It is evident, from well established prin- 

 ciples of electrical action, that if the outside of a house were encased 

 entirely in a coating of metal, the most violent discharge which might 

 fall upon it from the clouds would pass silently to the earth without 

 damaging the house, or endangering the inmates. It is also evident, 

 that if the house be merely covered with a roof of metal, without pro- 

 jecting chimneys, and this roof were put in metallic connexion with 

 the ground, the building would be perfectly protected. To make a 

 protection, therefore, of this kind, the Professor advises that the me- 

 tallic roof be placed in connexion with the ground, by means of the 

 tin or copper gutters which serve to lead the water from the roof to 

 the earth. For this purpose, it is sufficient to solder to the lower end 

 of the gutter a riband of sheet copper, two or three inches wide, sur- 

 rounding it with charcoal, and continuing it out from the house until 

 it terminates in moist ground. The upper ends of these gutters are 

 generally soldered to the roof; but if they are not in metallic contact, 

 the two should be joined by a slip of sheet copper. The only part of 

 the house unprotected by this arrangement will be the chimneys ; and 

 in order to secure these, it will only be necessary to erect a short rod 

 against the chimney, soldered at its lower end to the metal of the 

 roof, and extending fifteen or twenty inches above the top of the 

 flue. 



Considerable discussion in late years has taken place in reference 

 to the transmission of electricity along a conductor ; whether it passes 

 through the whole capacity of the rod, or is principally confined to 

 the surface. From a series of experiments presented to the Ameri- 

 can Philosophical Society, by Professor Henry, on this subject, it ap- 

 pears that the electrical discharge passes, or tends to pass, principally 

 at the surface ; and as an ordinary sized house is commonly fur- 

 nished with from two to four perpendicular gutters (generally two in 

 front and two in the rear), the surface of these will be sufficient to 

 conduct, silently, the most violent discharge which may fall from the 

 clouds. 



Professor Henry also stated, that he had lately examined a house 



