It is only necessary to make a metallic communication between this iron work and the lead which carries off the water. This frequently reaches to the ground or very near it. From the bottom of this, the metallic communication should continue to the nearest water, or at least to very moist ground; though where it can be procured, water should be preferred. Care must be taken likewise, that metallic communications be added to those parts of the lead which serve to convey the water from the top, as do not already touch or come near each other. And these may be either of lead or of copper wire, such as before mentioned. In thunder storms attended with rain, sufficient in quantity to run off in streams, a great portion of the electric matter runs off in, and is dissipated by, these streams; and buildings are thus preserved from damage.

What happened to St. Bride's cannot but give us some apprehensions for that noble edifice St. Paul's. This is above 100 feet higher than St. Bride's, and therefore more in the way of accident from thunder storms. On its magnificent lantern is placed a cross of metal, which is inserted into the stone of the lantern; and this is supported by a truncated cone of brickwork, which arises from the arches of stone below. The cupola is covered with lead, which is continued to the spouts of the same material. These bring down the water to the stone gallery under the cupola, and end within about a foot of the stone. From hence the water is conveyed to a considerable distance, in a stone trough or channel to the leaden spouts; and these are carried down the building, and terminate, as I was informed on inquiry, in the common sewer. By this arrangement the metallic communication is interrupted. In a thunder storm, during rain, the water carries off in streams the electricity as perfectly as the most complete metallic communication would; but when there is no rain it is otherwise; and these interruptions are the great cause of danger. To lessen which, as far as we can conclude at present, it would be expedient to make, by the means of several copper wires, small rods, or pieces of lead, a metallic communication between the gilded cross, and the lead of the cupola: and again, from the leaden spouts of the stone gallery to those which bring the water thence; care being taken that from the bottom of these last there should be a metallic communication, if there should be found none at present, with the water in the common sewer. Thus, without much expense, a complete metallic communication may be made between the top of St. Paul's church and the water; which had it been done at St. Bride's, the ravages so lately experienced had in all probability been prevented.

From considering the circumstances of this thunder storm, I cannot but be of opinion, that the injury done to St. Bride's prevented mischief to St. Paul's. St. Bride's is a very high building, and within a small distance nearly west of St. Paul's. When this distance is considered, and that the lightning came in the direction of St. Bride's to St. Paul's, and that when the thunder cloud

came near the former, it exploded there, and parted with much of its force; what was left did no damage to the latter, though the latter is a much higher and more exposed building, and having a metallic cross at its top.

I have recommended as metallic conductors copper wires of the size of a goose quill; as, when of that thickness, they may easily be bent to any direction, and where thought necessary, any number may be employed. I consider this as a kind of standard, from what Dr. Franklin wrote to Mons. Dalibard, of Paris, on this subject.* He observes, in a church which suffered greatly by lightning at Newbury, in New England, that though a small wire was beaten to pieces by lightning, and dissipated by its force, the rod of a pendulum conducted the whole without being melted or otherwise injured by it; and that, great as the quantity was in this instance, and which utterly destroyed the small wire, no damage was done to the building, as far as the small wire and the pendulum of the clock extended: and in the remarkable instance mentioned by Mr. Kinnersley, in his letter to Dr. Franklin, where a brass wire of about two lines thick, ten inches long, and terminating in a very acute point, was inserted into the iron rod, about two inches and a half only of its top were melted by the lightning; the remaining part of it transmitting the lightning without being fused by it.

You will observe in this disquisition, that I have no where mentioned the apparatus attracting the lightning. I have avoided introducing the term attraction here, operating as an active principle; as I consider the apparatus purely passive, and only affording, from the aptness of its parts to that purpose, an easy and uninterrupted passage to the lightning, and thereby preventing its violent efforts.

You will pardon, sir, this long digression in relation to St. Bride's Church as it gives so positive and explicit an answer to part of your seventh question; such a one as could not, without the late thunder storm, have been furnished, at least from hence: to wit, that without a proper apparatus, weathercocks placed at the tops of any buildings are dangerous to them in thunder storms; but more especially to powder magazines. The accidents which have lately happened to St. Bride's and South Weald Churches, if considered as great electrical experiments, furnish very important, and, I flatter myself, useful conclusions. They are too hazardous and expensive, however, to wish to see often repeated.

If the erecting of an apparatus of this sort should become general in countries where thunder storms are frequent, and often attended with mischief, though damage should be really averted by it, the operation of the apparatus would be unseen, and therefore unknown, unless in such rare instances as that mentioned by Mr. Kinnersley. To make its effects apparent, as has been hinted to me by Dr. Heberden, a very deservedly eminent physician here, if chains are Philosophical Transactions Abridged," vol. x. "Philosophical Transactions Abridged," vol. x.

employed as metallic communications, instead of wires or rods, whenever the lightning comes near enough to affect the apparatus in a considerable degree, it will, without mischief, be visible in the dark, by its sparkling and snapping in its passage, at the links of the chain. The effects of the apparatus may be observed in another manner. If the metallic commuications are by the means of a wire or single rod, there may be, in some parts of its length, in any place convenient for observation, a space left where the metal is discontinued; but this space should not exceed two inches. The two extremities of the metal at this interruption should be furnished with brass knobs not less than an inch in diameter. By this method though the effects of the apparatus would not be considerably lessened, they might be observed. For at times when no lightning was visible, but when clouds replete with it came near the apparatus, or rain from them fell upon it, there would be a snapping from one of the brass nobs to the other. When indeed the lightning was near, there would not only be this snapping, but, if the cause was great, a stream of fire would be seen, as in M. Romas's kite,* to pass from one of these to the other, as the best and nearest conductor. If danger however is apprehended, a piece of chain may be always at hand to be hung occasionally on the upper knob, so as readily to fall in contact with the lower. Otherwise, if while the metallic communication is divided, though when entire it is apprehended it may be touched with safety, a person should touch the rod above the division, and at the same time touch or come very near the rod below the division with any part of his body; and at the same instant if a smart stroke of lightning affected the apparatus, he would certainly be destroyed, as happened to Professor Richmann, at Petersburg; the lightning going through his body from one part of the apparatus to the other, which it is believed it will not do while the metallic communication is complete.

8. I have not heard that there has been here of late any particular mode of buildings adapted to powder magazines, to diminish the shock of the explosion in case of accident: nor do I believe that any attention has been here given in constructing these buildings, to prevent, by an apparatus of this kind, the effects of lightning.

An Account of the Effects of Lightning on St. Bride's Church, Fleet-street, on the 18th of June, 1764. By EDWard Delaval, Esq., F.R.S.

THE Construction of this spire is somewhat similar to that of an apparatus purposely contrived to draw the lightning from the clouds, as it runs up towards a point, and ends in a metal vane and cross, the figure of which, as well as the materials they consist of, seem calculated to admit the lightning with the least resistance. The first marks of it are seen at the top of the copper cross, which is

• 16 Philosophical Transactions Abridged," vol. xi.

the highest part of the building, the gilding is by the explosion partly torn off and partly discoloured, so as to differ remarkably from the rest of the cross where the gilding is very well preserved. Some small pieces of solder are melted; and all this part appears as if it had been exposed to the fire. The lightning seems to have entered here, and to have been conducted thence by an iron spindle twenty feet in length, and two inches in diameter; of which ten feet were surrounded by the copper ball, vane, and cross; and the lower half was inclosed in a groove cut through the middle of the solid stones which composed the upper part of the spire, and rested on the bottom of that groove, which was sunk five inches deep into the lowest of those solid stones: this last mentioned stone being three feet broad and one deep. The interval between the sides of the spindle and the groove made to receive it was filled up by melted lead poured in between them.

The lightning accumulated in the metal, having its passage towards the earth strongly resisted at this place, has in expanding itself formed a hole, by bursting off from the lower part of the spindle the stones contiguous to it on that side. At each of the angles of the metal, the stone on which it rested is cracked, which probably was occasioned by the lightning issuing with greater freedom from those parts, than from the flat surface. No part of the spindle is in the least injured by the lightning, notwithstanding the great quantity which, from its effects, appears to have been accumulated in it.* From hence, as low as to the cornice, it seems to have been conducted along the surface of the spire, which was wetted by the rain that had fallen in the morning, before the lightning; and having been accumulated in the iron bars, in discharging itself from them, it has made the greatest explosion at this place.

Under this part the freedom of its passage seems to have been hindered by all the dry stonework underneath, which was defended from the rain by the cornices: and it appears from some experiments which I formerly made,+ that dry freestone, when warmed to a certain degree (which probably does not exceed the heat which the stones of buildings acquire in hot weather) resists the passage of the electric fluid or lightning so strongly, that with plates of that stone, instead of glass, I performed the Leyden experiment. Under the cornice, the lightning descended only by leaping from one iron to another; and at every leap its force seems to have been weakened, and at last to have been quite dissipated.

On examining the inside of the steeple, beginning from the top, the first effect of the lightning that appears is a hole in the stonework, beginning immediately above an iron bar which served to support the top of the window or opening, and running upwards

In the year 1750, the stones surrounding this spindle were so much damaged, that there was a necessity of taking them down and rebuilding that part of the spire. The cause of this was not known at that time: it is probable that it was occasioned in the same manner as the present accident. + "Philosophical Transactions Abridged," vol. xi.

towards the two cross iron bars: this, when viewed from the outside of the church, is seen to have spread round most of the lower part of the spire, so that it seems in great danger of falling. The next stroke is about four feet below: at this place four iron bars lie horizontally across the spire, and are tied together by chain bars which are inclosed in the stonework: where the end of one of the cross bars is inserted in the stone, the lightning has burst open a hole; and when the same is viewed at the outside, a great part of the cornice appears to be broken off. Where the two iron bars serving to support the top of the windows meet and are joined together, the lightning accumulated in them has broken off the pier by which they were inclosed. A bar of iron, which served to support the top of the window in the same manner as those last mentioned, twentyone inches long, clear of the stonework, and half an inch thick, is broken, and the stones immediately above it are shattered and disjointed. The sills of two windows of this story are torn off from iron bars which lay beneath them.

An iron bar, No. 1, about twenty-five inches long, was inclosed nine inches deep in the stonework of the pier, separating the east arch from the arch next it towards the north: the end of this bar joins at a right angle another bar, No. 2, which is laid across the arch. The lightning accumulated in the iron No. 1, which was inclosed in the stonework, has burst off all the stone that surrounded it, and part of the pier adjoining. The flaw is continued downwards, meeting with smaller iron cramps in its way. At the next arch, lying immediately under the last mentioned one, an iron was inclosed in the stone in the same manner as the bar at No. 1: the stone is torn off from this iron exactly in the same manner as at No. 1: but the damage has not reached much farther than the stone which was contiguous to, and covered this bar. As the bottom of this arch the sill stone, which covered some cramps of iron, is torn off from its place. At the next arch under this, the force of the lightning seems to have been much diminished, a small part of one stone only being broken.

From the wall at the west side of the south window of the belfry, some stones are thrown down one chalky stone in particular is reduced into an impalpable powder, and the wall under the west window is almost covered with the powder: this stroke seems to have been directed towards the bells, one of which is very near the place damaged the bells have not been examined, nor can they, it is said, without danger of shaking the spire by their motion. This is the lowest mark which is left of the effects of the lightning.

In every part that is damaged, the lightning has acted as an elastic fluid, endeavouring to expand itself where it was accumulated in the metal and the effects are exactly similar to those which would have been produced by gunpowder pent up in the same places, and exploded. Among many other stones thrown to a considerable distance by these explosions, one weighing above seventy pounds was removed fifty yards eastwards from the steeple, where it