VOL. LXVIII.J PHILOSOPHICAL TRANSACTIONS. 343 



without any other change of circumstances, the wheel having been turned the 

 same number of times, I suffered the model to pass : the rounded end, in this 

 case, was not struck. However, the instant after it had passed, the quantity of 

 the charge that remained in the cylinder was taken in the same manner by the 

 hand ; on which the sensation was more violent than in the last experiment. 



bth Observation. — From tlie last 2 experiments it appears, that though every 

 circumstance was the same, excepting the diflFerent terminations of the 2 con- 

 ductors, yet the pointed one only was struck ; though they were both of the 

 same length, and passed at equal distances from the cylinder. Hence we col- 

 lect, that the quantity of lightning discharged from the great cylinder into the 

 point, when an explosion happened, was considerably greater than the quantity 

 discharged into the rounded end, when there was no explosion. 



At the first rise of a difference in opinion, respecting the proper termination 

 and length for conductors, I was prevailed on by some learned members of the 

 R. s., in the year 1764, to publish my sentiments on that subject. Accordingly, 

 in a letter addressed to the marquis of Rockingham * (after slating several 

 reasons against the use of points, as I suppose they invited the lightning) I there 

 recommended that conductors should not only be rounded at their ends, but be 

 made considerably shorter than those which Dr. Franklin contended for, and 

 indeed should not exceed the highest part of the building. In the following 

 experiment, however, I did not place the pointed conductor below, nor on a 

 level with the highest part of the building, but above it, even ^ of the length 

 of that in tiie 12th and I3th experiment. 



Exp. 14. The model being thus furnished, and every thing else put exactly 

 into the same circumstances as in the 13th experiment, the great cylinder was 

 charged by 20 turns of the wheel. On letting go the model, it passed the 

 cylinder at the distance of 7 inches, without being struck : but the charge that 

 remained in the cylinder at the instant after the model had passed it, was so 

 considerable, that there appeared no material difference whether the model thus 

 circumstanced was suffered to pass or not. 



6th Observation. — This last experiment shows, that a thunder-cloud may pass 

 a conductor so circumstanced without the latter being struck, or suffering the 

 least injury ; which it will not do in other circumstances, that is, when the 

 conductor is pointed, and raised 10 feet above the building. 



Exp. 15. On repeating the 14th experiment, but with a rounded conductor, 

 which was f of the whole length of that in the 12th experiment (all other cir- 

 cumstances remaining the same) and after charging the cylinder by an equal 

 number of turns, it passed also without being struck. In this case, the remain- 



» Phil. Trans, vol. S'l.— Orig. 



