Proceedings of the Polytechnic Association. 809 



Dr. L. Bradley said he wished to call attention to one point, and 

 that was, as copper and steel have different degrees of expansibility, 

 what would be the effect of the heating and cooling of these two 

 metals? He apprehended there would be a serious change in their 

 molecular arrangement. A lightning rod should have a bright point 

 at the top, and good communication with the earth, and if it is at 

 the proper height, it will protect a building from common lightning, 

 as it will pass down the rod silently into the earth. But when a 

 thunder-bolt, or what is called " ball-lightning," occurs, there is no 

 lightning rod that will carry it to the ground ; no lightning rod will 

 protect a building against that kind of lightning. 



Dr. Boynton replied that he had never known of " ball .lightning " 

 being near a good lightning conductor. The lightning rod is to 

 prevent the thunder-bolts of the heavens from accumulating. This 

 wire is so light that it can be stretched to nearly a straiglit line, 

 and in this condition it has stood the heat and cold for over a 

 year. 



Dr. Vanderweyde remarked that he noticed a lightning rod on a 

 house in Troy last winter. The rod was split and the painters put 

 plenty of paint in the crack, thus destroying communication with the 

 earth. Another rod on a church in Albany had the end of it resting 

 on a wood-pile, the rod was a very fine iron one. In Germantown, 

 Philadelphia, a building was struck by lightning, and he examined 

 the rod, which he found the end to be embedded only eight inches in 

 dry sand. The end of a lightning rod should go to where there was 

 moist earth, or to a well or stream of water. The lightning rod 

 here shown seems to be a very perfect one, free from oxydation and 

 continuous ; and no doubt when the French government, or Academy 

 of Science make another report, it will be in favor of the one of Moses 

 G. Farmer. 



Prof. J. A. Whitney said that those who live in the city know but 

 little of the effects of lightning. Here lightning seems to be a 

 small affair, but the damage done in the country makes lightning 

 rods very popular there. He had seen a small building on the farm 

 on which he was reared struck by lightning and shattered to pieces. 

 The ordinary iron lightning rods, made in joints are often put up by 

 men who know very little about them, and hence we see so many 

 useless on-es. This is due partly to their mode of construction, and 

 the want of skill in those who put them up. The lightning rod 

 of Mr. Farmer seems to overcome these objections, as a ffaw cannot 



