624 PHILOSOPHICAL TRANSACTIONS. [aNNO 176g. 



The coinmittee recommend therefore, that a bar of iron, of an inch and a quarter 

 square, may be placed between the pine-apple, or the lead in contact with it, and 

 the upper part of this stair case; and that another iron bar, similar to this last, 

 may be adjusted so as to pass from the bottom of the stair-case to the lead on 

 the roof of the church. The roof, as has been already mentioned, communicates 

 with the leaden pipes, and these with the ground. 



These towers, from their near situation to the cupola, which is a building so 

 much higher, may possibly be less liable to mischiefs from lightning than if they 

 were erected at a more considerable distance. As the direction of the lightning 

 is, however, uncertain, from a variety of causes, as also to what extent one 

 building will protect another, the committee are of opinion, that this apparatus 

 to the towers will be expedient. 



It is to be remarked, that wherever iron is employed as a conductor of light- 

 ning, especial care must be taken to prevent its becoming rusty ; as, from being 

 long exposed to the moist atmosphere, it will be corroded to a considerable 

 depth: and so much of the iron %s is corroded ceases to be of use as a con- 

 ductor; the committee therefore have, in directing the size of these iron bars, 

 made some allowance for the waste of the iron by rust. 



The size, as well as number, of the iron bars recommended here by the com- 

 mittee, are only to be considered as applicable to St. Paul's, and not as a standard 

 for any church or building of less dimensions ; as in these last, conductors of a 

 smaller size, and fewer in number, may answer the purpose as securely as the 

 larger. But St. Paul's church is particularly circumstanced ; it is an edifice not 

 only of great height, but its cupola, to say nothing of the lead on the body of 

 the church, presents a large surface of metal to the clouds; on which account it 

 is very liable to receive greater quantities of the electric fluid; and, from large 

 quantities of such an elastic power, great mischiefs may arise to this magnificent 

 building, in consequence of obstructions the fluid may meet with in passing 

 through it. For these reasons we have recommended very large conductors, 

 that it may pass through them into the ground, as readily as it enters. 



These, Sir, are our sentiments in regard to the matter, referred to us by the 

 Royal Society, on the request of the Dean and Chapter of St. Paul's. If they 

 should be acceptable to the Society, and by their means to the Dean and Chap- 

 ter ; and if, by being carried into execution, they should at all contribute to the 

 preservation of that noble fabric, it will be a great satisfaction to us. We are, 

 with very great respect. Sir, your most obedient, humble servants, W. Watson, 

 B. Franklin, B. Wilson, John Canton, Edward Delaval. 



