about of an inch, more or lefs; the distance appearing to be generally lefs when the power is greateft; and whether they pierce or only make impreffions upon it, they leave evident marks of motion from two different parts, and in two contrary directions.

When two flips of tin-foil are put into the middle of the quire, including two or more leaves between them, if the electricity be but weak, the counteracting powers only ftrike against the flips, but leave an impreffion; if the fhock be ftronger, one of the flips is pierced, but feldom both; and it appeared in general to Mr. Symmer, that the power which iffued from the outfide, acts with greater force, than that which proceeded from within.

To break thick pieces of glass. Place a thick piece of glafs on the ivory plate of the univerfal difcharger, fig. 15, pl.1, and a thick piece of ivory on the glafs, on which a weight from one to feven pounds is to be placed; take off the balls a, b, bring the points of the wires against the edge of the glafs, and pafs the discharge through the wires, by connecting one of the wires with the hook of the battery, and forming a communication, when the battery is charged, from the other wire to the ball. By this operation the glafs will be broken, and fome part of it fhivered to an impalpable powder. When the piece of glafs is ftrong enough to refift the fhock, the glafs is often marked by the explofion with the moft lively and beautiful colours.

Place a piece of very dry white wood between the balls of the univerfal difcharger, the fibres of the wood to be in the fame direction with the wires, pass the shock through them, and the wood will be torn to pieces; or run the points into the wood, and then pafs the fhock through them.

To melt wires by the electrical fluid, you

ought

ought to have a battery containing at least 30 fquare feet of coated furface; you may then connect the outfide coating with a wire of about th of an inch in diameter, and from 12 to 24 inches in length; faften the other end of the wire to one of the balls of the difcharging rod; on making the difcharge, the wire will become red hot, then melt and fall upon the floor or table in glowing globules. Sometimes the fparks are thrown to a confiderable diftance, if the force of the battery be very great, they will be entirely difperfed by the explosion.*

* For a further variety of experiments, fee my Essay on Electricity.

LECTURE

LECTURE XLVIII.

ON LIGHTNING, AND THE USEFULNESS OF METALLIC CONDUCTORS TO DEFEND BUILDINGS FROM IT'S EFFECTS.

No

OTHING can be more natural than to pafs from the electrical battery to lightning itself, for the former feems to be more than an imitation; it is nature invested with her own attire. The light and found accompanying thefe phenomena, when exhibited on the great fcale of nature, are indeed fo awfully fublime, that we can fcarce with propriety reflect on the weakness of thofe, who, in ages lefs informed, fuppofed it to be the immediate minister of vengeance from an angry Deity. They are now more rationally confidered, as the natural means of refloring a neceffary equilibrium; the rough difcords of nature productive of general harmony.

The phenomena of lightning are always furprifing, and fometimes terrible; there is no appearance in which there is more diverfity, no two flashes being obfervad exactly fimilar to each other.

On a fummer's evening, it may often be perceived to play among the clouds; this kind is quite inoffenfive, and is not accompanied with thunder.

When the lightning is accompanied with thunder, it is well defined, and has generally a zigzag form; fometimes it only makes one angle like

the

the letter V, fometimes it appears like the arch of a circle. But the most formidable and destructive form which lightning is ever known to affume, is that of balls of fire. The motion of thefe is very often easily perceptible to the eye, but wherever they fall, much mifchief is the refult of their explosion. The next to this, in it's deftructive effects, is the zig-zag kind; for that fpecies, whofe flashes are indiftinct, and whofe form cannot be easily obferved, is feldom known to do much hurt. You may confider the colour of lightning as an indication of it's power to do mifchief, the paleft and brightest flashes being most destructive.

There feems to be a kind of omniprefent property in the ziz-zag kind of lightning when near. If two perfons are ftanding in a room, looking different ways, and a loud clap of thunder happens, accompanied with the ziz-zag lightning, they will both diftinctly fee the flash, not only by that indiftinct kind of illumination of the atmofphere, which is occafioned by fire of any kind, but the very form of the lightning itself, and every angle it makes in it's courfe will be as diftinctly perceptible, as though they had looked directly at the cloud from whence it proceeded. If a perfon was at that time to be looking on a book, or other object which he held in his hand, he would diftinctly fee the form of the lightning between him and the object. This property feems peculiar to lightning.

The effects of lightning are generally confined within a small space; and are feldom fimilar to those which accompany explosions of gunpowder, or of inflammable air in mines. Inftances of this kind, however, have occurred; the following is one of the most remarkable of which we have any diftinct account: "August 2, 1763, about fix in the evening, there arofe at Anderlight, about a league

league from Bruffels, a conflict of feveral winds borne upon a thick fog. This conflict lafted four or five minutes, and was attended with a frightful hiffing noise, which could be compared to nothing but the yellings of an infinite number of wild beafts. The clould then opening, difcovered a kind of very bright lightning, and in an inftant the roofs of one fide of the houfes were carried off and difperfed at a distance; above 1000 large trees were broke off, fome near the ground, others near the top, fome torn up by the roots; and many both of the branches and tops carried to the diftance of. 60, 100, or 120 paces; whole coppices were laid on one fide, as corn is by ordinary winds. The glafs of the windows which were most exposed was fhivered to pieces. A tent in a gentleman's garden was carried to the diftance of 4000 paces; and a branch torn from a large tree, ftruck a girl in the forehead as fhe was coming into town, at the distance of 40 paces from the trunk of the tree, and killed her on the spot."

Thunder-ftorms will fometimes produce moft violent whirlwinds, fuch as are by fome philofophers attributed to electricity; nay, even occafion an agitation of the waters of the ocean itfelf; and all this too after the thunder and lightning. has ceafed. Of this we have the following inftances. "Great Malvern, October 16, 1761. On Wednesday last we had the moft violent thunder ever known in the memory of man. At a quarter past four in the afternoon, they were furprised with a moft fhocking and difmal noife; 100 forges all at work at once, could fcarce equal it. Upon the fide of the hill about 400 yards to the fouth-west, there appeared a prodigious fmoke, attended with the fame violent noife, as if a volcano had burst out of the hill; it foon defcended, and paffed on within about 100 yards of the fouth VOL. IV.

Bb

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