344 PHILOSOPHICAL TRANSACTIONS. [ANNO 1778. 



ing charge in the cylinder was something less than in the last experiment. 



yth Observation. — This is a further instance of the advantage derived from 

 having rounded terminations of a given length on a building, compared with 

 pointed ones, that are only 2 or 3 feet longer. 



Exp. 16. On charging the great cylinder as before, that is, by 20 turns of 

 the wheel, and when the model, without any conductor on it, was let go, there 

 was no explosion in or on any part of it, during the time of its passing by the 

 cylinder ; though the model itself was properly connected with metal from the 

 top of the roof to the bottom of it, and afterwards to the well. — Exp. 17. But 

 when the experiment, with the long pointed conductor on the model, was 

 repeated, and after the wheel had been turned an equal number of times, the 

 point was struck, as it passed the cylinder ; and, at the same instant also, a very 

 small stream-like explosion appeared between the two cramps at the corner of 

 the model, darting as it seemed from one to the other, in a direction that was 

 rather particular. This stream-like appearance, I apprehended, was nothing 

 more than the effect of a small explosion in consequence of the motion of the 

 model. 



Sth Observation. — The 13th experiment showed, that the corner of the 

 model, where the 2 cramps were inserted, passed safely by the charged cylinder, 

 without affording even the least luminous effect ; and consequently proved, that 

 in such circumstances the 2 cramps could not possibly be struck, because the 

 charge in the cylinder remained the same, or very nearly so, after the model had 

 passed. 



Qth Observation. — But in the 17th experiment, the pointed conductor was 

 fixed in its place on the model, just like that at Purfieet ; when not only the 

 point was struck, as the model passed the cylinder ; but, at the same instant, a 

 small explosion was seen between the 2 cramps at the corner. That this light 

 between the cramps arose from a different cause than what had been suggested 

 by the 2d Purfieet committee, appeared from some circumstances accompanying 

 that effect. For example, these cramps had no connection with the gutter or 

 spouts next them, but were quite separate, and at the distance of 6 or 7 inches 

 from any metallic communication. And it is well-known to philosophers, that 

 lightning always passes where it meets with the least resistance ; they also know 

 that the least resistance in the present instance nmst have been along the con- 

 ductor at the top to the hips, gutters, and spout, and so on to the wire at the 

 bottom to the well. According to this law, the cramps themselves, then, were 

 not properly circumstanced to receive the fluid as it passed to tiie earth, on 

 account of the metallic communication, described above, being interrupted 

 more than 6 inches. 



Exp. 18. To each end of a slender substitute made of wood, about 11 feet in 



