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 D d VOL III. means of a chain, with the positive and negative part of a machine, and in a darkwill see, when the machine ened room, you 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 seen accounts for the darting and undulating motion which takes place between the opposite parts of the heavens. The aurora borealis is the most beautiful and brilliant in countries in the high northern latitudes, as in Greenland and Iceland. Charles. I remember the lines on this subject: By dancing meteors then, that ceaseless shake Tutor. The aurora borealis that was seen in this country on the 23d of October, in the year 1804, is deserving of notice. At seven in the evening a luminous arch was seen from the centre of London, extending from one point of the horizon, about S. S. W. to another point N. N. W. and passing the middle of the constellation of the Great Bear, which it, in a great measure, obscured. It appeared to consist of shining vapour, and to roll from the south to the north. In about half an hour, its course was changed; it then became vertical, and about nine o'clock it extended across the heavens from N. E. to S. W.; at intervals, the continuity of the luminous arch was broken, and there then darted from its south-west quarter, towards the zenith, strong flashes and streaks of bright red, similar to what appears in the atmosphere during a great fire in any part of the metropolis. For several hours the atmosphere was as light in the south-west as if the sun had set but half an hour; and the light in the north resembled the strong twilight which marks that part of the horizon at Midsummer. Thomson, speaking of the aurora borealis, and other meteors, says -Silent from the north, A blaze of meteors shoots; ensweeping first Relapsing quick, as quickly re-ascend, James. How do you account, sir, for the Will-with-the-wisp, or Jack-a-lanthorn, that is close to the ground where the air is thickest? Tutor. This is a meteor which seldom appears more than six feet above the ground; it is always about bogs and swampy places, and these, in hot weather, emit what is called inflammable air, which is easily inflamed by the electric spark. These, therefore, as you shall see in our chemical experiments, we can as readily imitate as the aurora borealis. In some parts of Italy, meteors of this kind are frequently very large, and give a light equal to that of a torch. Water-spouts, which are sometimes see n at sea, are supposed to arise from the power of electricity. |