shock of lightning reduced in one part of it to the thickness of a slender wire only. Since then we are at all times ignorant of the quantity of lightning in the earth and its atmosphere; and the difference in the effects, between blunted and pointed ends, in-causing a discharge in our electrical experiments, appears to be as one to twelve, it is easy to comprehend the very great danger this noble fabric has probably escaped by having no pointed apparatus upon it.

From the above observations, I am naturally led to consider a part of the proceedings of the committee, respecting the magazines at Purfleet; when a certain number of conductors, with tapering points at the top, were resolved on, as necessary to protect the several buildings where the powder is deposited. For it was agreed on at the same meeting, that the board-house, which is a large building for the use of the board officers, and which stands considerably higher than the magazines, as was observed above, did not require any point at the top, because it was apprehended to be perfectly secure, by reason of the copings on the roof, the gutters and pipes to carry off the water being all of lead, and further, because those pipes communicated with two wells, which always contained water.

I was not a little surprised at this last resolution, which appeared to be so inconsistent with the former. Because, if points were necessary in one place, they ought to be so in another. And onthe other hand, if the board-house is secure by the leaden accidental conductors, which have no points, why ought not the magazines to be equally secure, when put into the same circumstances? I therefore enforced the inconsistency of such a resolution in the strongest terms. Notwithstanding which, the gentlemen at that time thought proper to confirm their resolution. However, at the next meeting of the committee, I observed that they had been pleased, in the mean time, to make an amendment in favour of points for the board-house; which amendment was no sooner proposed than approved of.

Why my observation was rejected at the preceding meeting, I must leave to the judgment of others. But it certainly carries an appearance as if manifest contradiction, on further reflection, must have been the cause of that alteration.

And I am inclined to believe, from some gentlemen of the committee expressing their opinion, "of its being a matter of mere indifference whether blunted or pointed conductors were made use of," that they have not considered this subject with all the due attention which so important an object deserves. For if our experiments show that points, from the nature of their shape, and other circumstances attending them, resist the attacks of this fluid less than blunted ones, and that blunted conductors, of proper dimensions, are sufficient to convey away the lightning safely, whenever it attacks them, why should we have recourse to a method which is at best uncertain, and which some time or other may be productive of the most fatal effects?

But perhaps no argument can be brought with more force against

the principle of points, than Dr. Franklin's own words, which are published in his experiments, p. 481, where he declares positively, "buildings that have their roofs covered with lead, or other metal, and spouts of metal continued from the roofs into the ground, to carry off the water, are never hurt by lightning; as whenever it falls on such a building, it passes in the metals, and not in the walls."

This is the case with the British Museum, a building also of considerable consequence, where there are no other conductors than what are formed by the copings, gutters, and pipes, which are all of lead, and communicate with the ground. Now it is from the great quantity of metal contained in the several pipes, together with the other circumstances attending them, that I considered that building, in a former paper laid before the Royal Society, as being sufficiently secured from those dangerous accidents. But if any gentleman should be disposed to entertain a doubt about it, or indeed of any other part of my reasoning on this subject, a declaration of those doubts may be attended with good consequences, as they will necessarily open the door to a more minute investigation.

I have now, sir, gone through the reasons which I proposed to lay before the Royal Society for the rejecting of points. And I am very sorry, in the course of this letter, to have been under the necessity of mentioning any differences in opinion, which passed between the members of the committee to whom this important matter was referred. I think, however, I shall stand excused to the society and the public, when it appears, as I hope it now sufficiently does, what my motive has been; namely, to state clearly, and impartially, the objections which I conceived to lie against pointed conductors; and to disclose, without any reserve, the principles on which such objections are grounded.

P.S. Mr. Delaval, who was one of the committee, has given me leave to insert his opinion on this subject, which is this :-That he concurs with me in thinking that such conductors as are elevated higher than the buildings to which they are applied, or are pointed at the top, are improper and dangerous. He was desirous of delivering his opinion at the committee, but as the meetings of it were held in the summer only, his absence from London prevented his attendance.

NOTE.-Mr. Gould acquaints us in his letter that he examined the four conductors in the lantern and stone gallery of St. Paul's church, the morning after the lightning happened. That no marks whatever appeared on the conductor to the south, which was the first he attended to. That he next examined the conductor to the west, and observed a thick rust lying on the pavement in the stone gallery, as if it had been cleaned off from the conductor with a tool: that several parts of the iron appeared black, particularly the screws or nuts something like the effects left by gunpowder on iron or steel, or a smoky fire. That the conductors to the north showed no marks, no more than that to the south. But that, on examining the con

ductor to the east, he found stronger marks abundantly, than on the west conductor, it being much blacker; particularly on the nut and screws: the rust lying in great quantities on the pavement. And the extreme part of the conductor, that goes into the water trunk, seemed like a piece of iron newly taken out of a forge by a smith, without working it on the anvil.

Mr. Gould has since added to the account in his letter some circumstances which I apprehend ought not to be omitted. He says, that where the end of the conductor, on the east side, points towards the water trunk, a stone surrounds part of it, leaving an interval, half an inch wide or more, between them, and about four or five inches long, which is a little more than the breadth of the conductor that this interval was filled up with dirt, and had been so for some time, occasioned by frequent showers of rain washing the pavement in the stone gallery: that, after the lightning happened, he observed a hole was made through the dirt, one quarter of an inch in diameter, and about two inches in length: that the hole was close to the iron; and that, on stooping down his head, he perceived a very disagreeable smell of sulphur from the stone, dirt, and conductor, particularly the last.

On hearing this account, Mr. Delaval and myself, a few days ago, went and examined the conductors again; but more carefully than before. For, on causing the stone to be removed, which covered the top of the water trunk, we had an opportunity of examining near two feet more of the iron which points to the water trunk than we could perceive before this stone was removed, when we observed that the conducting iron did not touch the lead. We likewise observed that there was a very thick coat of rust all over that part of the iron; particularly at the end next the lead, where the water entered the trunk. As the necessity of attending to these circumstances will be obvious to any one, who is but in the least degree acquainted with these researches, the danger of neglecting them will be seen in the strongest light, by the gentlemen of the committee who recommended the conductors for the security of that cathedral.

A Letter to Sir JOHN PRINGLE, Bart. Pr. R.S., on Pointed Conductors. Dec. 17, 1772.

SIR,-Having heard and considered the objections to our report, concerning the fixing pointed conductors to the magazines at Purfleet, contained in a letter from Mr. Wilson to Sir Charles Frederick, and read to the Royal Society, we do hereby acquaint you, that we find no reason to change our opinion, or vary from that report.— We have the honour to be, &c., H. Cavendish, W. Watson, B. Franklin, J. Robertson.

Papers relative to an Accident from Lightning at Purfleet,
May 15, 1777.

A Letter from Mr. BODDINGTON, Secretary to the Board of Ordnance, to Dr. HORSLEY, Secretary to the Royal Society, with Two Enclosures from Mr. NICKSON, Storekeeper at Purfleet, giving an Account of the Accident.

Office of Ordnance, May 31, 1777. SIR, I am directed by the lieutenant-general, and the rest of the principal officers of the Ordnance, to transmit to you the copies of the reports and plan received from Purfleet, on occasion of some damage done by lightning; which reports and plan they desire you will please to lay before the Royal Society.-I am, &c.,

To Dr. Horsley, Sec. R. S.

JOHN BODDINGTON.

To Sir Charles Frederick, Knt. of the Bath.

Purfleet, May 16, 1777. HONOURABLE SIR,-Yesterday afternoon, we had much rain and distant thunder; but at six a very heavy cloud, in passing over the house, presented us with part of its contents, which struck the northeast corner of the house on one of the cramps that held the copingstones together, forced off about a square foot of that stone and one brick, and has displaced about a cube foot of brick-work underneath. It has not been yet discovered that any of the conductors have acted during the passage of that cloud, though the flash and report were both very great. One of my servants was out of doors by the coach-house at the same time, and narrowly escaped falling by the strength of the flash: the others were in the house, but were much frightened. My son says, that there is a dent in the cramp, on which the lightning fell, and I intend to preserve it as a curiosity. If the conductor on the house has acted, it is imperceptible, as I am informed. I thought this account would be acceptable to you from honourable sir, &c., EDWARD NICKSON.

To the Right Hon. Lord Amherst, Lieut.-General of his Majesty's Ordnance, &c.

Office of Ordnance, Purfleet, May 20, 1777. MY LORD,-Iu obedience to your lordship's commands of the 19th instant, directing me to report concerning the accident that happened to the Board's house by lightning on the 15th, I beg leave to acquaint your lordship, that on that day there had been much rain and distant thunder; but, about six o'clock in the afternoon, a very heavy cloud hung over the house for some time, which I looked at from the back parlour window, and, it being quite calm, made me suspect that some of our conductors might find employment from it. I had not been long at the window before a violent flash of lightning and clap of thunder came together; and, as soon as the rain would permit any

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body to move about, one of the labourers brought me some pieces of stone and a brick, which were struck off from the coping on the parapet wall of the building from the north-east corner. On my son's coming home, I desired him to go and view the top of the house. On his return he told me, that the lightning had struck one of the cramps that held the coping together, and had made a dent in the lead of the cramp, and the stone adjoining to it, as if struck by a musket-ball; that the quantity of stone thrown down might amount to about a square foot; and that it had disturbed about a cube foot of brick-work underneath: and, according to your lordship's commands, the distance from the point of the conductor on the house to the part struck has been measured by him this day, and amounts to forty-six feet. All the conductors at this place are pointed, and it has not yet been discovered that any of them have acted on this occasion. If your lordship should want any farther explanation, my son waits on you with a small drawing of the elevation of the east front of the house, and of the part struck, which I hope will be satisfactory to your lordship, and to the honourable Board,-I am, &c., EDWARD NICKSON.

The Report of the Committee appointed by the Royal Society, for Examining the Effect of Lightning, May 15, 1777, on the Parapet Wall of the House of the Board of Ordnance, at Purfleet, in Essex.

The iron cramp on which the lightning fell was cemented into the coping stones on the parapet wall, near the north-east corner, with lead and on that lead, at one end of the cramp, there appeared to have been a small fusion; the end of the lead, and part of the 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 seven inches of the plate, which communicated with the gutter, and served as a fillet 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 seven inches of stone, brick, and mortar, it fell on the corner of the plate of lead above-mentioned, 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 performed their office. At the distance of seven and a half feet from the place stricken, a large leaden pipe went down from the gutter to a cistern of water in the yard. The fain, Mr. Nickson informed us, had fallen plentifully for some time before the stroke; so that the mortar, bricks, &c., did probably form an imperfect conductor, for the distance of seven inches, between the iron cramp in the coping stones and the filleting lead above-mentioned.