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those which we have received from Paris and Berlin, they are the only ones that the last summer here has produced; and as they were made by persons worthy of credit, they tend to establish the authenticity of those transmitted from our correspondents.

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SECTION III.

Considerations to prevent Lightning from doing Mischief to great Works, high Buildings, and large Magazines*.

By Mr. Wilson, F.R.S.

LONG experience, since the discovery by Dr. Franklin, has now established a truth among philosophers, that lightning, like the electric fluid, passes more freely through iron, copper, and other metals, than through dry wood, stone, or marble. Instances of this truth are innumerable: and to be convinced of it, we need only trace the late violent effects of lightning on St. Bride's church, and the houses in Essex-street, &c. For, on examining these buildings, it appears that there are certain thick bars of iron, through which the lightning has passed, without producing any visible effects; and, on the contrary, in certain parts where the junctions of those bars with the stone, or wood, are made, there the lightning, rushing from the iron, has broke the stone to pieces, and shivered the wood. From the like experience we also learn, that if the iron is too slender for conducting the lightning, it is either dashed into pieces, or exploded like gun-powder; just in the same manner as we are able, by the electric power, to break and dissipate in vapour a very slender wire. Bars of metal, of a proper thickness, and conveniently disposed, seem therefore necessary for the security of such buildings.

It is to be noted, that the mischiefs caused by lightning are not always owing to its direction from the clouds to the buildings, or other eminences, and thence to the earth; but sometimes, on the contrary, from the earth, buildings, and other eminences, to the clouds. For the principle on which its direction depends, appears to arise from the restoration of a certain equilibrium, in a subtile

* See farther on this subject, the articles in Section v.

and elastic fluid, previously disturbed by various causes. Now, according to the laws of elastic fluids, the endeavour to restore the equilibrium of such a fluid, will be in that direction where the resistance to its passage happens to be the least. On this principle we therefore see a necessity, either to open a passage for it to go freely through, by placing certain bars of metal properly, or to stop the passage of the fluid through such buildings entirely. The last method would be dangerous to put in practice; because, if high buildings were so secured, the lightning would then attack the lower buildings, which are far more numerous, and probably would destroy a greater number of people, cattle, &c. Whereas, if the first method is preferred, the high buildings will then tend to protect the lower ones more effectually; and may with pro. priety be considered as so many pipes to carry off the lightning quietly, either from the earth to the clouds, or from the clouds to the earth. And that several proper conductors are necessary to carry off the lightning, more readily than some of the accidental or partial conductors in a large town are capable of, appears from this; that we are able to collect small quantities of the electric fluid, with a slender apparatus in our hands only; whilst it is exposed in the street, garden, or other open place, during the hovering of such clouds as occasion violent lightning.

From repeated observations of this kind, there is reason to believe, that the quantity of lightning at particular times, is so very great, that it would be dangerous to invite it to any buildings, and that unnecessarily, in the most powerful manner we are able; by suffering the several conductors to end in a point at the top. On which account it is apprehended, that pointed bars, or rods, of metal, ought always to be avoided. And as the lightning must visit us some way or other, from necessity, to restore the equili brium, there can be no reason to invite it at all; but, on the con trary, when it happens to attack our buildings, we ought only so to contrive our apparatus, as to be able to carry the lightning away again by such suitable conductors, properly fixed, as will very little, if at all, promote any increase of its quantity.

To attain which desirable end, in some degree at least, it is proposed, that the several buildings remain as they are at the top; that is, without having any metal above them, either pointed or not, by way of a conductor. On the inside of the highest part of

such building, and within a foot or two of the top, it may be pro per to fix a rounded bar of metal, and to continue it down along the side of the wall to any kind of moisture in the ground.

But if the building happens to be mounted with an iron spindle, for supporting a vane, or other ornament, and it should not be conve. nient to have it taken away, then the bar of metal ought to com. municate with that spindle. And as to the diameter of such a metal bar, it will probably depend on the height of the building; for it is apprehended the great church of St. Paul's, to complete the partial conductors (which are the metallic cross, ball, gallery, dome, &c.) and secure it effectually, would require a bar of metal two inches 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 appear from a late instance taken notice of in St. Bride's church, by Mr. Delaval, and Dr. Watson, where an iron bar, 2 inches broad, and half an inch thick, or more, was bent and broken asunder by the violence of the lightning. The Eddystone. 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, two feet in diameter, with a chimney of the same metal, passing through it down to the second 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 Captain Dibden, commander of a merchant ship, who says, that in the year 1759, 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 twenty miles, his conductors, or guard, stopped at a small chapel, five miles from the last place, to shelter themselves from the heavy rain which fell during a violent thunder-storm. That the chapel had no steeple or tower belonging to it, but stood on an eminence, with three or four poor low houses near it. That soon after they were thus sheltered, a violent flash of lightning struck two soldiers dead, who had been leaning against the wall of the chapel, between two 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 four feet high, and about three feet broad, and in that part only against which they rested.

That Captain 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 observed a square bar of iron near the hole, and on the ground, about four feet long, and 14 inches 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 to pieces. That this bar was joined in the middle to one end of another bar, about one foot long, and one inch thick, which laid horizontally, and, passing to the wall, had been there fastened with lead. That the lightning, in rushing along the inclined bar, had wasted or reduced its thickness in some places very considerably, insomuch that it looked like a burnt poker which had been long used; and broke the bar into two pieces, about an inch above the joining of the lesser bar, the ends of which had a burnt flaky appearance. That the other parts of the bar were changed in colour to a grey, or whitish hue, resembling iron after it has been exposed to a violent heat and then suffered to cool. That the horizontal bar had also undergone an extraordinary change by the lightning, but particularly at that end next the wall of the chapel, it being reduced from one inch in diameter to the size of a slender wire, but tapering towards the wall. That when the soldiers rested against the wall, their heads were about the same height with the shortest bar; and, from what he can recol. lect, were very near being opposite to that end which was inserted in the wall. That the two soldiers were forced from the wall at the same instant by the lightning; so that their feet, which were

one yard or mere from it, were nearest to the wall, and their heads the farthest off. That their flesh appeared very black. That their clothes were burnt and scorched in many parts, and their belts shrivelled up, as if they had been exposed to a large fire. That Captain Dibden, and other people, felt a disagreeable kind of an electric shock, at the same instant that the soldiers were killed.

Captain Dibden gave an account also, that he was lately at Virginia, 1763 that the inhabitants of Norfolk had changed their opinions in respect to fixing of wires and small rods of iron on the tops of their houses; from the frequent instances they have lately had of their being melted, or destroyed, by the violence of the lightning and that now they adopted, in their stead, rods of iron from half an inch thick to three-fourths of an inch thick, or more. That those rods ended in a point at the top, and extended from three feet above their houses down to the ground; and that many houses had one of these conducting irons at each end. The Capt. added, that though the pine trees are considerably higher than the oaks in the American woods, yet the oaks are the oftenest attacked by the lightning: and that he does not remember any oaks grow. ing among the pine trees, when the latter have suffered by light. ning, which must be owing to the greater resistance arising from the unctuous nature of the pine trees.

[Phil. Trans. 1764.

SECTION IV.

Thunder-storms remarkable from their violence, or the pecu. liarity of their effects.

1. Strange effect of Thunder and Lightning on Wheat and Rye in the Granaries of Dantzic.

By M. Christopher Kirby.

You doubtless know how much this city is famed for its numerous and convenient granaries, it being the repository of all sorts of grain the fruitful kingdom of Poland affords. In those granaries are laid up chiefly wheat and rye, in parcels of twenty to

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