VOL. LIV.] PHILOSOPHICAL TRANSACTIONS. 149 



tallic cross, ball, gallery, dome, &c.) and secure it effectually, would require a 

 bar of metal 1 indhes diameter, if not more, and a building like the British 

 Museum, one considerably less. But it appears there is no occasion for any at 

 that repository, as it is already provided, though from accident, like many other 

 buildings, with very effectual conductors. The copings of the roof, and the 

 several spouts, which are continued from it into the ground, being all of lead. 



That conductors ought to be thicker than is generally imagined, seems to ap- 

 pear from a late instance taken notice of in St. Bride's church by Mr. Delaval 

 and Dr. Watson, where an iron bar 1^ inches broad, and 4- an inch thick, or 

 more, was bent and broken asunder by the violence of the lightning. The Ed- 

 dystone Lighthouse, which stands on a rock surrounded by the sea, the work of 

 Mr. Smeaton, was thought to be an object very likely to suffer by lightning; 

 and the more so, as the top of it consisted of a copper ball 1 feet in diameter, 

 with a chimney of the same metal, passing through it down to the 2d floor, but 

 no farther. Directions were therefore given to make a communication of metal 

 from the lowest part of the copper chimney down to the sea; which was executed 

 accordingly about the year 1760, or soon after the building was finished. Now 

 if, instead of the copper ball, a pointed bar of metal had been put in its place, 

 or above it, and communicated with the conducting matter below, there is no 

 saying what might be the consequence of so powerful an invitation, to an edifice 

 thus particularly situated. 



Since the former part of this paper was communicated to the r. s., that is, 

 on the 5th of August, 1764, I received the following account from Capt. Dib- 

 den, commander of a merchant ship, who says, that in the year \75g, he was 

 taken by the French, and carried prisoner to Fort Royal in Martinico. That in 

 removing him thence some time after, and on foot to St. Pierre, which is about 

 20 miles, his conductor, or guard, stopped at a small chapel 5 miles from the last 

 place, to shelter themselves from the heavy rain which fell during a violent thun- 

 der storm. That the chapel had no steeple or tower belonging to it, but stood 

 on an eminence with 3 or 4 poor low houses near it. That soon after they were 

 thus sheltered, a violent flash of lightning struck 2 soldiers dead, who had been 

 leaning against the wall of the chapel between 2 buttresses, and not far from 

 the rest of the company, being all on the leeward side of the chapel. That it 

 made an opening in the wall about 4 feet high, arid about 3 feet broad, and in 

 that part only against which they rested. 



That Capt. Dibden, along with other persons, entered at this hole immediately 

 after, to see if any other damage had been done to the chapel. That they ob- 

 served a square bar of iron near the hole, and on the ground, about 4 feet long, 

 and \\ inch thick, making an angle with the wall, as they suppose, to support 

 the upper part of an inclined tombstone, which was also thrown down and broken 



