VOL. LIX.J PHILOSOPHICAL TRANSACTIONS. 621 



and Chapter of St. Paul's, the Society did us the honour to appoint us a com- 

 mittee to examine that magnificent structure, and, as far as our experience 

 would enable us, to prevent mischief to it from lightning, by a properly disposed 

 apparatus ; we lay before you the following as our opinion on it, to be communi- 

 cated, if you think proper, to the Royal Society. And here, sir, you will permit 

 us to take notice of, and acknowledge, the obligations we were under to Mr. 

 Mylne, a very worthy member of this society, who is surveyor of St. Paul's, and 

 attended several meetings of the committee. This gentleman furnished us with 

 a great variety of information, in regard to the structure of the several parts of 

 this fabric, which, without his assistance, could not easily have been obtained. 



As all metals are now known readily to conduct or transmit the electric fluid, 

 or, which is the same thing, lightning through them ; the large quantity of lead, 

 and some iron, disposed in different parts of St. Paul's church, will, by having 

 its several parts connected, where there is at present no such connection, prevent 

 the erecting a considerable part of the apparatus, which otherwise we should 

 judge absolutely necessary. 



We are of opinion that, caeteris paribus, all buildings on the same level are 

 liable to be injured by lightning in proportion to their height : and that the 

 danger is increased by crosses, weather-cocks, or pieces of metal, in any form, 

 placed upon or near their tops, unless there is a complete metallic communica- 

 tion from these to the bottom of the building, which metal should terminate 

 either in water or moist ground. 



In St. Paul's church, the objects of our more particular attention were the 

 dome and its lantern, and the two towers at the west end. The roof over the 

 body of the church, being completely covered with lead, will, we conceive, pre- 

 vent mischief to it from lightning; and the more so, as the lead on the roof 

 joins to that of the several leaden spouts, which come down the sides of the 

 building, and terminate in the ground at a considerable depth. For our more 

 certain information, one of these spouts was examined; and it was found to 

 descend perpendicularly about 3 feet under the surface of the earth : and then, 

 after being laid about 7 feet in an inclined direction, it ended in a brick drain, 

 which communicates with the sewer. These circumstances induce us to con- 

 clude, that what has been just now described is a sufficient metallic communica- 

 tion between the roof of the church and the ground. 



No part of this whole fabric seems to be in so dangerous a situation of being 

 injured by lightning as the stone lantern placed above the dome. This danger 

 arises not only from its height, but from the different pieces of metal in different 

 parts of it, being at present detached and separated from each other. This stone 

 lantern is supported by a truncated cone of brick-work, of no more than 1 8 



