458 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



diameter of its pinion of 6, f for a pinion of 7, f for one of 8, -^ for one of 

 10, -jV, or a quarter, for a pinion of 12, and so on. 



XLIf^. New Experiments on the Leyden Phial, respecting the Termination of 

 Conductors. By Benj. Wilson, Esq., F. R. S. p. ggg. 



In the 64th volume of the Philos. Trans., there is a paper of Mr. Henly's 

 on the subject of conductors, containing several experiments, intended to show 

 that pointed terminations are preferable to spherical ones for securing build- 

 ings, &c. from accidents by lightning. On those experiments Mr. W. made 

 some observations, and particularly on the 5th, where a point and ball were 

 placed at the same distance from a sphere of copper, so as to make part of the 

 circuit in the Leyden experiment. In the description of that experiment Mr. W. 

 objected to the 2 chains employed, because the metallic communication was, by 

 that method, considerably interrupted, on account of a want of contact between 

 the several links composing the chains. He did not then repeat the experiment, 

 because the particular circumstances attending the Leyden phial appeared very 

 unlike what happen in nature; and therefore he contented himself with pointing 

 out the several circumstances in which they differed; and in observing that, 

 according to Mr. Henly's account, the point did not protect the rounded end 

 from being struck, which it ought to have done, if Dr. Franklin's philosophy 

 was well founded. 



Since that time an occcasion has offered which made it necessary to try this 

 particular experiment. The occasion alluded to arose from a late investigation of 

 Mr. Nairne's experiments by Dr. Musgrave, who was desirous of having 

 that experiment repeated; because, as it stood in Mr. Henly's account, it 

 seemed to contradict a considerable part of the doctor's reasoning. Not being 

 furnished with an apparatus to make the experiment, he requested Mr. Cavallo 

 to assist him with his; and though it was not so complete for the purpose as 

 could be wished, yet it answered sufficiently well to show, that an attention to 

 the circumstance of a perfect communication in this experiment was very material 

 to discover the truth ; and that the want of it had probably occasioned the ball 

 to be struck in preference to the point, as related by Mr. Henly: for on 

 employing a wire instead of the chains, the point was struck at more than 3 

 times the distance of the ball. 



Seeing so great a difference between the two experiments, Mr. W. procured 

 such an apparatus as he thought would be the least exceptionable for determining 

 the fact on which these different appearances seemed to depend; namely, a 

 perfect and an imperfect circuit of communication with the Leyden phial. The 

 circuit of communication was divided into two parts. A bent rod of brass, with 

 a ball of the same metal, -f- of an inch in diameter, screwed on to its upper 



