172 ANNUAL OF SCIENTIFIC DISCOVERY. 



discharge; hence it offers a. comparatively' unobstructed channel 

 for the passage of the electricity, and, of course, prevents any 

 dangerous accumulation. The rod anticipates the danger; it 

 gradually and safely transmits to earth an amount of electric en- 

 ergy which, if discharged at once, would have manifested intense 

 violence. If the powder in a cannon were burned grain by grain 

 during a few seconds, it would not even move the ball, and yet 

 the same force has been expended as when exploded at once. He 

 had been inclined to consider the electricity of the cloud to bear 

 to that of the earth the relation of intensity to quantity ; that an 

 equivalencj' of force may exist between all. Quantity in the gal- 

 vanic battery has its equivalent force in the intense flash of the 

 induction coil. It may also be admitted that quantity in the earth 

 is represented by intensity on the points of the rod. In this case, 

 an identity of action is established between the points and the 

 cloud. It need hardly be said that to insulate a rod from the 

 building it is intended to protect is useless, if not worse. The 

 house is in a state of electric tension as well as the rod, and the 

 object of the rod is to relieve all such tension. To do this it must 

 be in electric communication with the house. Indeed, the insula- 

 tion is after all a sheer pretence, and is practically impossible, for 

 the building and rod are connected throuo^h the earth. If the 

 roof is metallic all the better. It affords surface to diffuse the 

 force, and sharp edges and innumerable points to discharge it. 

 No better rod can be constructed to connect such a roof with the 

 the earth than its water conductors. Pass iron or copper rods 

 from these into moist earth, or better, connect with the water-pipes 

 of a city, or the water of a well, or the gas-pipes, and insurance 

 against lightning would be profitable to the company insuring. 



LIGHTNING-RODS. 



At the 1868 meeting of the American Association, Mr. James 

 Bushee presented a paper on the defects of lightning-rods. 



The use of metallic rods for the protection of life and property 

 from the destructive effects of atmospheric electricity is acknowl- 

 edged to be efficient when the laws of electrical science are re- 

 garded. The writer of the paper had had various opportunities 

 for observing the effects of lightning, and his attention was early 

 called to the singular fact that a large majority of the buildings 

 struck and injured were those having rods attached, and instances 

 liave occurred where houses with rods have been affected with the 

 current, while houses in the vicinity, without rods, have escaped. 

 Hence some had doubted the efficacy of lightning-rods, and 

 others had rejected them altogether as wrong in principle and 

 positively dangerous. The Avriter believed, however, that there 

 was, in these implements, a remedy for the effects of lightning. 



The question thus arose, What is the cause of the numerous 

 casualtius from lightning where rods are used, and how, if possi- 

 ble, can such disasters be prevented ? To answer this question he 

 had for 10 or 12 years examined the cases occurring in Worcester, 



