340 Intelligence and Miscellaneous Articles. 



the proportion of acid correspondent to the formula BO G C Q H 3 O 

 would be 75 - 2 per cent. The product obtained was evidently a little 

 impure, and contained, besides some boracic methylic aether, some of 

 the compounds of boracic acid with the pyrogenous compounds, 

 which it is so difficult to separate from pyroxylic spirit. — Ibid. 



ON A SIMPLE METHOD OF PROTECTING FROM LIGHTNING, 

 BUILDINGS WITH METALLIC ROOFS. BY PROF. HENRY. 



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 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 con- 

 fined to the surface. From a series of experiments presented to the 

 American Philosophical Society, by Professor Henry, on this subject, 

 it appears that the electrical discharge passes, or tends to pass, prin- 

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

 furnished with from two to four perpendicular gutters (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 

 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 j^sed along this hori- 

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



