334 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



adjoining stone, being indented about half an inch in diameter, and a quarter of 

 an inch deep, as though a musket-ball had been fired against them. The iron 

 cramp was situated over a plate of lead, and the ends of it, which were inserted 

 in the stone, came within 7 inches of the plate, which communicated with the 

 gutter, and served as a tillet to it: this gutter was a part of the main conductor 

 of the building. When the lightning had quitted the iron cramp, and had 

 passed through 7 inches of stone, brick, and mortar, it fell on the corner of 

 the plate of lead abovementioned, as appeared by the fusion of a very small 

 portion of it discovered by pulling out the bricks, mortar, &c. on purpose to 

 examine into this particular. From this place no further effect of the lightning 

 could be traced; the metallic conductors to the earth having effectually per- 

 formed their office. At the distance of 74- feet from the place stricken, a large 

 leaden pipe went down from the gutter to a cistern of water in the yard. The 

 rain, Mr. Nickson informed us, liad fallen plentifully for some time before 

 the stroke; so that the mortar, bricks, &c. did probably form an imperfect con- 

 ductor, for the distance of ^ inches, between the iron cramp in the copeing 

 stones, and the filleting of lead abovementioned. 



At the termination of the iron cramp in the copeing stone, a piece of the 

 stone, with one brick, was stricken off; and a few other bricks were loosened, 

 and removed less than half an inch from their places. The damage done to the 

 parapet of the building is so inconsiderable, that it would scarcely deserve 

 notice, was it not an evident proof that the metallic communication with the 

 earth, hath, in this case, efi^ectually prevented any further injury. 



The conducting rod on the ridge, near the centre of the house, showed no 

 marks of its having been afi^ccted by the lightning in this case: and it is remark- 

 able, that the surface of one of the hip-rafters, A\ inches in diameter, covered 

 with lead (communicating with the gutter) and reaching within 28 inches of the 

 place stricken, seems not to have been at all affected. 



The method we would recommend of preventing similar accidents to the 

 parapet of this building for the future, is the following: let a channel of the 

 same size with the cramps be made from cramp to cramp in the copeing stones, 

 quite round the building: let this channel be filled with lead, and let a metallic 

 communication by plates about 6 inches broad be made from that lead in 4 places 

 (one at each side or corner of the parapet) to the filleting of lead which is in 

 contact with the gutter, which gutter is part of the main conductor to the 

 building. W. Henley, T. Lane, E. Nairne, J. Planla. 



June 19, 1777. 



3. Mr. IVilsons Disstnl from the ahove Report. — When this important sub- 

 ject was first debated in the Purfleet committee of 1772, a passage was quoted 

 from Dr. Franklin's philosophical publications, respecting the nature of sucii 



