428 PHILOSOPHICAL TRANSACTIONS. [aNNO 17/8. 



in regard to the termination of conductors for the preservation of buildings from 

 the effects of lightning. Some gentlemen think that they should not terminate 

 in a point, but be blunted ; and also that they should not exceed the highest part 

 of the buildings ;* they also think, that to prevent lightning from doing mis- 

 chief to great works, high buildings, and large magazines, the several buildings 

 should remain as they are at top, that is, without having any metal above them, 

 either pointed or not, by way of a conductor ; but that on the inside of the 

 highest part of such a building, and within a foot or 2 of the top, it may be 

 proper to fix a rounded bar of metal, and thence continue it down along the side 

 of the wall to any kind of moisture in the ground. -j- Others again are of a 

 directly contrary opinion ; thinking a conductor should not only terminate in a 

 point, but be considerably elevated above the highest part of the building. ;}: As 

 it most certainly would be of great consequence to mankind to know which is the 

 most eligible of these opinions, I have attempted, by what I could learn from 

 the artificial lightning of our electrical machines, to determine which method is 

 best to secure buildings from the effects of lightning : whether 1 have succeeded 

 I leave to the judgement of others to decide from the following experiments and 

 observations, which are submitted with all due deference. 



In the apparatus vised in the following experiments, the diameter of the glass 

 cylinder was 18 inches; the length of the conductor, which was of wood covered 

 with tin foil, was 6 feet, and its diameter 1 foot. At the end of this conductor 

 was screwed a brass ball, called c, of 4-i- inches diameter. This conductor 

 when charged by the glass cylinder, being intended to represent a cloud charged 

 with electricity or matter of lightning, will, for distinction sake, be called the 

 artificial cloud, in the following experiments. There was a brass rod, called d, 

 on a stand covered with tin foil, having a good metallic communication with the 

 earth ; at one end of this rod were screwed other rods, terminating with different 

 sized balls, or a rod terminating with a point. This rod was moveable in a 

 socket, in order that it might be placed with its termination at different distances 

 from the ball at the end of the artificial cloud. As the terminations on this rod 

 were to receive, from our artificial cloud, the stroke or sparks of our artificial 

 lightning, it will be called the receiving rod in the following experiment. The 

 receiving rod with its stand was intended to represent a conductor to a house, on 

 which different terminations might be placed. 



Before relating the experiments it may be proper first to premise, that electric 



* Mr. Wilson's new Experiments on the Nature and Use of Conductors, p. 7. — Orig. 

 t Mr. Wilson's Letter to the Marquis of Rockingham, Phil. Trans, vol. 54, p. 247. — Orig. 



I Ibid. p. '203. — Orig. 



