354 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



method of firing gunpowder by a luminous stream of the matter of lightning 

 surely merits the most serious attention; and more especially in those cases where 

 pointed conductors are fixed to secure magazines of gunpowder from such 

 accidents. In repeating the last experiment, tliere were one or two instances 

 where the powder was fired without making use of the long wire; but never 

 with the great cylinder alone: for we were obliged to connect it with the brass 

 drums by means of a wire 10 or 12 feet long. It was however a considerable 

 time, (10 minutes or more) before the experiment succeeded even with this last 

 apparatus. This was not the case with tinder; for it fired pretty readily, and 

 sometimes with the great cylinder alone. . ■ ; 



Exp. 50. Before the apparatus was taken down in the Pantheon, attempts 

 were made several days to fire gunpowder, but without success, except in one 

 instance, which was attended with some difficulty. This failure seemed to be 

 owing to a variety of causes, the chief of which appeared to be moisture that 

 affected the silk lines, and perhaps the powder itself However, when the coiled 

 wires on the silk lines were properly joined to the long wire, as in the 49th 

 experiment, it was found that gunpowder could be fired very readily. This is 

 another proof of the increase of velocity by increasing the length of the wire. 

 The explosion of gunpowder, in the particular manner related above, without 

 the assistance of the Leyden charge, and even without a sjjark, is an effect which 

 could not easily be deduced from reasoning on any experiments hitherto made; 

 for though gunpowder has been frequently fired with the Leyden charge, yet 

 there is a difference in the 1 cases. 



5. A Report of the Committee, appointed by the Roi/al Society, to consider 

 of the most Effectual Method of Securing the Powder Magazines at Purjleet, 

 against the Effects of Lightning; in Compliance with the Request of the Board 

 of Ordnance. — It being referred to us to consider, whether any thing more than 

 what was formerly directed by the committee of the r. s. in the year 1772 can be 

 done, for the preservation of his majesty's magazines at Pui-fleet: having atten- 

 tively examined the experiments and observations of Mr. Wilson, contained in a 

 paper referred to the society by the Board of Ordnance; and having maturely 

 considered the subject at large, we submit it as our opinion : 



1. That it is very improbable, that the powder magazines, guarded in the 

 manner in which they are at present, should receive any damage from lightning. 



2. That they would be still less liable to be injured if 3 other elevated pointed 

 rods, similar to those already erected, were to be fixed on the roof of each of 

 the 5 magazines, between the extreme rods, at equal distances from each other, 

 with 3 strips of lead, about one foot in breadth, strongly connected with them, 

 and carried down the roof, from the ridge to the ea\es, on each side of the build- 

 ing; thence two of them to be continued into the earth, and to terminate at the 



