Scientific Intelligence — Meteorology. 375 



generally a lull of wind at the line of minimum pressure, and some- 

 times a calm. When the wind changes to the west, the barometer 

 generally begins to rise. There is generally but little wind near the 

 line of maximum pressure, and on each side of that line the winds 

 are irregular, but tend outwards from that line. The fluctuations 

 of the barometer are generally greater in the northern than in the 

 southern parts of the United States, and greater in the eastern than 

 in the western parts.* (Ibid.) 



5. Protection from Lightning of Houses with Metallic Roofs. — 

 Professor Henry 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 

 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 damaging the house, or endangering the inmates. It also 

 is evident, that if the house be merely covered with a roof of metal, 

 without projecting chimneys, and this 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 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, 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 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 sixteen 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 

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

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

 furnished with from two to four perpendicular gutters (generally two 

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



* We should like to see evidenco of the second part of this statement. 



