622 FHILOSOPHICAL TKANSACTIONS. [aNNO \76Q. 



inches, or 2 bricks thick. To the honour however of the architectural sagacity 

 of Sir Christopher Wren, who was formerly our president, this support of the 

 lantern, which has already stood much above half a century, has not in the 

 least given way in any of its parts. How far it would sustain the violence of a 

 stroke of lightning will, it is to be hoped, never be tried: and what we have now 

 to propose will, we flatter ourselves, lessen the probaljility of its being injured 

 by it. The first object of our attention, therefore, was to make a complete me- 

 tallic communication between the cross, placed over this lantern, and the leaden 

 covering of the great dome ; as from its height, if any lightning was in its neigh- 

 bourhood, it would most probably affect the cross. 



This cross with the ball, both composed of metal, are supported by, and con- 

 nected with 7 iron rods. These descend perpendicularly through the small leaden 

 dome, which covers the lantern, and are inserted into and pass through a strong 

 frame of timber, placed horizontally under that dome. The lower extremities 

 of these iron rods are fastened to the under surface of this timber frame with iron 

 nuts and screws. 



From this timber work, several large iron bars, placed at some distance from 

 the ends of the above-mentioned iron rods, descend obliquely, and are fixed in 

 the stone- work of the lantern. The upper ends of each of these oblique iron 

 bars pass through the frame of timber before mentioned, and are fastened to its 

 upper surface with iron nuts and screws. Between these iron bars and the leaden 

 covering of the great dome, there is at present no metallic communication. To 

 this arrangement, therefore, is owing the danger from lightning, which the 

 committee apprehends that this part of the building is liable to. To obviate 

 which, we are of opinion, that 4 additional iron bars, each not less than an inch 

 square, should te securely placed over the frame of timber before mentioned in 

 such a manner, that one end of each of these 4 additional iron bars may be in 

 contact with one of the perpendicular iron rods, and the other end of each be in 

 contact with one of the iron nuts and screws, which fasten the obliquely descend- 

 ing iron bars to this frame of timber. At the bottom of these oblique iron bars, 

 just above where they are inserted into the stone-work, the committee recom- 

 mends, that a ring, made of bar iron, of about an inch square, should be placed 

 60 as to be fastened to, and be in contact with, these iron bars. 



From this proposed ring to the upper part of the lead which covers the great 

 cupola, the distance is about 48 feet. In this space, we are of opinion, that 4 

 iron bars should be placed, each not less than an inch square. These siiould be 

 fixed within the lantern in such a manner, that the upper end of each should 

 be fastened to, and in contact with, the iron ring before mentioned, and their 

 lower ends in contact with the lead on the upper part of the cupola ; from which 



