432 PHILOSOPHICAL TRANSACTIONS. ("aNNO 1778. 



only -j^-Trpart of an inch diameter: on charging the artificial cloud, it struck to the 

 ball D, as in the first experiment, viz. 17-ro- inches. 



Observation 1. — From the first 3 experiments it appears, that the artificial 

 cloud strikes at distances greater as the termination of the conductor is more 

 blunted, or as it terminates with the larger ball; and that the striking distance is 

 less as the end of the conductor tends more to a point; and in the 4th experi- 

 ment, that when the end of the conductor is pointed, the point is not struck at 

 any distance whatever: but continues luminous to a certain distance, carrying 

 off silently the electricity of the artificial cloud. It seems from these experi- 

 ments, that pointed conductors are to be preferred before those terminating with 

 a large ball, the pointed one depriving the cloud silently of its electric fire; 

 whereas the ball receives the electric fire in a strong spark. And in the 5th 

 experiment, where a point projects but -j-l of an inch from a ball of 4 inches 

 diameter, neither the ball, nor peint projecting from it, is struck at any distance. 

 This seems to show the utility of a pointed rod, even if it projects but a small 

 distance above the highest part of a building. The 6th experiment shows, that 

 a point within the surface of a ball does not prevent the ball being struck. The 

 7th and 8th experiments likewise show, that our artificial cloud strikes to a ball 

 of 4 inches diameter, only at the distance of 6-^ inches, when the point is 

 drawn out Q inches from the 3-i inch ball, placed opposite to the side of the 

 artificial cloud; and that when the point projects only 1 inch, that then it 

 strikes to the 4 inch ball at i6-^ inches distance. 



May we not from these last 2 mentioned experiments conclude, that the more 

 elevated our pointed conductors are, the greater is the chance of preserving our 

 buildino-s from the effects of lightning? For here the point being elevated oi- 

 projecting Q inches out of the ball, representing the highest part of a building, 

 was found continually depriving the artificial cloud of its electric fire to such a 

 degree that it would not strike half the distance that it did when tiie point was 

 elevated only 1 inch. And from the Qth experiment we learn, that the con- 

 ductor terminating in a point acts at a far greater distance than one terminating 

 with a ball, in carrying otf the electric fire, or matter of lightning from the 

 artificial cloud. And though the point was luminous so far, yet there was no 

 distance whatever at which the artificial cloud would strike to it. 



From the 10th and 1 Ith experiments we learn, that the metallic part of the 

 conductor being separated or discontinued is the reason that the artificial cloud 

 strikes to the point; and that it strikes farther to the point as the number of 

 the separations are increased; and that if the metallic communication with the 

 moist earth be made complete, then the charged cloud will not strike to the 

 point. When a conductor to a building, terminating in a point, has been 

 struck, Mr. N, thinks that tlierc IkmI \\u\. t)een a complete and sufiicieiit metallic 



