372 PHILOSOPHICAL TRANSACTIONS. [aNNO 1773 



about 100 feet from the river, which rises in high tides within a {ew inches of 

 the level of the ground, its brackish water also soaking through to the wells that 

 are dug near to the buildings. 



The barrels of powder, when the magazines are full, lie piled on each other up 

 to the spring of the arches ; and there are 4 copper hoops on each barrel, which, 

 with a number of perpendicular iron bars, (that came down through the arches, 

 to support a long grooved piece of timber, wherein the crane was usually moved 

 and guided to any part where it was wanted) formed broken conductors within 

 the building, the more dangerous from their being incomplete, as the explosion 

 from hoop to hoop, in the passage of lightning drawn down through the bars 

 among the barrels, might easily happen to fire the powder contained in them. 

 But the workmen were removing all those iron bars (by the advice of some 

 members of this society, who had been previously consulted) ; a measure we very 

 much approve of. 



On an elevated ground, nearly equal in height with the tops of the magazines, 

 and 150 yards from them, is the house where the board usually meet. It is a 

 lofty building, with a pointed hip roof, the copings of lead down to the gutters, 

 from which leaden pipes descend at each end of the building into the water of 

 wells of 40 feet deep, for the purpose of conveying water forced up by engines to 

 a cistern in the roof. There is also a proof-house, adjoining to the end of one 

 of the magazines, and a clock-house, at the distance of feet from them, 

 which has a weathercock on an iron spindle, and probably some incomplete con- 

 ductors within, such as the wire usually extending up from a clock to its hammer, 

 the clock, pendulum rod, &c. 



The blowing up of a magazine of gunpowder by lightning, within a few years 

 past, at Brescia in Italy, which demolished a considerable part of the town, with 

 the loss of many lives, does, in our opinion, strongly urge the propriety of 

 guarding such magazines from that kind of danger; and since it is now well 

 known, from many observations, that metals have the property of conducting 

 lightning, and a method has been discovered of using that property for the 

 security of buildings, by so disposing and fixing iron rods, as to receive, and 

 convey away, such lightning as might otherwise have damaged them ; which 

 method has been practised near 20 years in many places, and attended with 

 success, in all the instances that have come to our knowledge, we cannot there- 

 fore but think it advisable to provide conductors of that kind, for the magazines 

 in question. 



In common cases, it has been judged sufficient, if the lower part of the con- 

 ductor were sunk 3 or 4 feet into the ground, till it came to moist earth; but 

 this being a case of the greatest importance, we are of opinion that greater 

 precaution should be taken. Therefore we should advise, that at each end of 



