1845] WRITINGS OF JOSEPH HENRY. 231 



ON THE PROTECTION OF HOUSES FROM LIGHTNING. 



(Proceedings of the American Philosophical Society, vol. iv, pp. 179, 180.) 



June, 20, 1845. 



Professor Henry made a communication relative to a simple 

 method of protecting from lightning buildings covered with 

 metallic roofs. 



On the principle of electric 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 principles 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 dam- 

 aging the house, or endangering the inmates. It is also evi- 

 dent, that if the house be merely covered "with a roof of 

 metal, without projecting chimneys, and this roof were put in 

 metallic connection with the ground, the building would be 

 perfectly protected. To make a protection therefore of this 

 kind the Professor advises that the metallic roof be placed 

 in connection with the ground by means of the tin or cop- 

 per gutters which serve to lead the water from the roof to 

 the earth. For this purpose it is sufficent to solder to the 

 lower end of the gutter a ribbon of sheet copper, two or three 

 inches wide, surrounding 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 chim- 

 neys; 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 



