charged as often as you please, but the wood will remain in its place, because the electric fluid runs through the wire to %, and makes its way by the chain to the outside of the phial.

Charles. Then if x be supposed the weathercock of the church, the lightning having overcharged this, by its endeavours to reach another conductor, as cz, forced away the stone or stones represented by a b c d?

Tutor. That is what I mean to convey to your minds by the first experiment; and the second shows very clearly that if an iron rod had gone from the weathercock to the ground, without interruption, it would have conducted away the electricity silently, and without doing any injury to the church.

James. How was it that all the stones were not beaten down?

Tutor. Because, in its passage downwards, it met with many other conductors. I will read part of what Dr. Watson says on this fact, who examined it very attentively:

"The lightning," says he, "first took a weathercock, which was fixed at the top of the steeple, and was conducted without injuring the metal or any thing else, as low as where the large iron bar or spindle which supported it terminated; there the metallic communication ceasing, part of the lightning exploded, cracked and shattered the obelisk which terminated the spire of the steeple, in its whole diameter,

and threw off, at that place, several large pieces of Portland stone. Here it likewise removed a stone from its place, but not far enough to be thrown down. From thence the lightning seemed to have rushed upon two horizontal iron bars, which were placed within the building across each other. At the end of one of these iron bars, it exploded again, and threw off a considerable quantity of stone. Almost all the damage was done where the ends of the iron bars had been inserted into the stone, or placed under it; and in some places, its passage might be traced from one iron bar to another.'

The thunder holds his black tremendous throne:
From cloud to cloud the rending lightnings rage;
Till, in the furious elemental war

Dissolv'd the whole precipitated mass
Unbroken floods and solid torrents pours.

THOMSON.

CONVERSATION XXXIX.

On Atmospheric Electricity--Of Falling Stars-Of the Aurora Borealis Of Water-spouts, and WhirlwindsOf Earthquakes.

Charles. Does the air always contain electricity?

Tutor. Yes; and it is owing to the electricity of the atmosphere that we observe a number of curious and interesting phenomena, such as falling stars; the aurora borealis, or northern lights; the ignis fatuus, or Will-with-thewisp.

James. I have frequently seen what people call falling stars, but I never knew that they were occasioned merely by electricity.

Tutor. These are seen chiefly in clear and calm weather it is then that the electric fluid is probably not very strong, and passing through the air it becomes visible in particular parts of its passage, according to the conducting substances it may meet with. One of the most striking phenomena of this kind is recorded by Signior Beccaria.-As he was sitting with a friend in the open air, an hour after sun-set, they saw a falling, or, as it is sometimes called, a shooting star, directing its course towards them, growing, apparently, larger and larger, till it disappeared not far from them, and, disappearing, it left their faces, hands, and clothes, with the earth and neighbouring objects, suddenly illuminated with a diffused and lambent light, attended with no noise at all.

Charles. But how did he know that this was only the effect of electricity?

Tutor. Because he had previously raised his kite, and found the air very much charged with the electric matter: sometimes he saw it ad

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vancing to his kite like a falling star; and sometimes he saw a kind of glory round it, which followed it as it changed its place.

James. Since lofty objects are exposed to the effects of lightning, or the electric fluid, do not the tall masts of ships run considerable risk of being struck by it?

Tutor. Certainly: we have many instances recorded of the mischief done to ships; one of which is related in the Philosophical Transactions; it happened on board the Montague, on the 4th of November, 1748, in latitude 42° 48' and 9° 3' west longitude, about noon. One of the quarter-masters desired the master of the vessel to look to the windward, when he observed a large ball of blue fire, rolling apparently on the surface of the water, at the distance of three miles from them. It rose almost perpendicular when it was within forty or fifty yards from the main-chains of the ship, it then went off with an explosion, as if a hundred cannon had been fired at one time, and left so strong a smell of sulphur, that the ship seemed to contain nothing else. After the noise had subsided, the main top-mast was found shattered to pieces, and the mast itself was rent quite down to the keel. Five men were knocked down, and one of them greatly burnt by the explosion.

Charles. Did it not seem to be a very large ball, to have produced such effects?

Tutor. Yes: the person who noticed it said it was as big as a mill-stone.

The aurora borealis is another electrical phenomenon: this is admitted without any hesitation, because electricians can readily imitate the appearance with their experiments.

James. It must be, I should think, on a very small scale.

Tutor. True: there is a glass tube about thirty inches long, and the diameter of it is about two inches; it is nearly exhausted of air, and capped on both ends with brass. I now connect these ends, by means of a chain, with the positive and negative part of a machine, and in a darkened room, you will see, when the machine is worked, all the appearances of the northern lights in the tube.

Charles. Why is it necessary nearly to exhaust the tube?

Tutor. Because the air, in its natural state, is a very bad conductor of the electric fluid; but when it is, perhaps, rendered some hundred times rarer than it usually is, the electric fluid darts from one cap to the other, with the greatest ease.

James. But we see the aurora borealis in the common air.

Tutor. We do so: it is, however, in the higher regions of the atmosphere, where the air is much rarer than it is near the surface of the earth. The experiment which you have just VOL. III. T