tained by an obferver, who, though in the fame room with the charged phial, was at the fame time in the middle of an electric circuit of two miles, and felt himself fhocked, at the fame inftant that he faw the phial difcharged. Another important difcovery by Dr. Watfon was, that the glass globes and tubes did not contain within themfelves the electric fuid which appeared on their excitation, but drew it from the earth and the bodies contiguous to the rubber, and in contact with it. Mr. Wilfon appears to have made the fame obfervation. Dr. Watson likewife difcovered, what Dr. Franklin had obferved about the fame time in America, the plus and minus ftates of electrified bodies. This fimple principle of the plus and minus, or the pofitive and negative states of the electric matter in bodies, became, in the hands of Dr. Franklin, as fruitful (if we make allowance for the different nature and importance of the fubject) as the principle of univerfal attraction in thofe of Newton. By the application of it, the Leyden phial, which had hitherto teemed with mystery and contradiction, had its moft glaring inconfiftencies reconciled and accounted for in the moft fimple manner. The doctor fhowed, that in the act of electrization, one fide of the phial (the infide, for inftance) was electrified pofitively; that is, had an additional quantity of the electric fluid thrown upon it; and that the other fide was electrified negatively; that is, was deprived of an equal quantity; and that the effect of that operation was not an increafe of the quantity of electric fire in the phial, but folely a change produced in the fituation of the natural quantity of electric matter belonging to it. Dr. Franklin's important difcovery of the identity of lightning, and the electric fire, I mentioned in my laft paper. This is one of the few capital difcoveries in electricity, for which we are not at all indebted to chance, but to one of those bold and happy ftretches of thought, in confequence of which thofe gigantic ftrides are made in fcience, which diftinguifh geniufes of a fuperior order. By this interefting and important discovery (the greateft, perhaps, that has been made in the whole compafs of philofophy fince the time of fir Ifaac Newton) we have it now in our power, by a fimple and cheap apparatus, to direct the courfe of the hitherto inevitable fulmen, and thereby, with respect to buildings at leaft, to deprive it of its power of hurting. By what fimple and flender inftruments, even the playthings of children, does the hand of Genius extort from Nature her choiceft fecrets. Thus Newton, by means of a foap-bubble, inveftigates the magnitude of the component particles of bodies, on which their colour depends; and Franklin, by railing a kite, difcovers the nature of lightning! The laft great difcovery of which I fhall take notice (and to which Mr. Canton led the way) is that of a new and very extenfive principle in electricity, by meffieurs Wilke and pinus, two foreign electricians. The principle, which, indeed, is founded on Dr. Franklin's theory of pofitive and negative electricity, is this; that the electric fluid, when there is a redundancy of it in any body, repels the electric fluid in any other body, within its influence, and drives it into the remote parts, or quite out of the body, if there be any outlet for that purpofe; thereby reducing the body to a ftate contrary to its own; that is, a negative ftate. On this principle they undertook to charge a plate of air, like a plate of glafs, and thereby to imitate, in the most perfect manner, the phenomenon of lightning. They fucceeded, by fufpending two large boards of wood covered with tin, with the flat fides parallel to one another, and fome inches afunder. On ele&trifying pofitively one of the boards (which may be confidered as metallic coatings to the two furfaces of the aërial plate), the other board became electrified negatively; and a perfon, touching this last with one hand, and bringing his other to the other board, received a hock through his body, as in the Leyden experi ment.--With this plate of air they made a variety of curious experiments. The two metal plates being in oppofite ftates, ftrongly attracted each other, and would have rufhed together, if they had not been kept afunder by strings. Sometimes, the electricity of both would be difcharged by a ftrong fpark between them, as when a plate of glafs burfts, and is perforated by too great a charge. A finger put between them promoted the difcharge and felt the fhock. If an eminence were made on either of the plates, the felf-difcharge would always be made through it; and a pointed body fixed upon either of them prevented their being charged at all. The ftate of these two plates, they excellently obferved, juftly reprefents the ftate of the clouds during a thunder-ftorm; the clouds being always in one ftate and the earth in the oppofite; while the body of air between them anfwers the fame purpose as the fmall plate of air between the boards, or the plate of glafs between the two metal coatings of the Leyden phial. The phenomenon of lightning is the bursting of the plate of air by a spontaneous discharge, which is always made through eminencies, and the bodies through which the discharge is made are violently fhocked. With refpect to the nature of the electric fluid, philofophers have entertained very different fentiments. Mr. Wilfon, and others, have fuppofed it to be the fame with the ether of fir Ifaac Newton; but Dr. Priestley is of opinion, that the electric matter is either phlogifton, or contains it. Perhaps we may be allowed to enlarge our views, and confider the fun as the fountain of the electric fluid; and the zodaical light, the tails of comets, the aurora borealis, lightning, and artificial electricity, to be its various and not very diffimilar modifications. But it cannot be expected, in the contracted space to which I am confined, that I can enlarge further on this fcience; a fcience on which fo many volumes have been written. I have been obliged to treat the fubject in a general light; as exhibiting a matter of curious fpeculation, to obferve the ignorance of the greatest men, for fo many ages, concerning phenomenons, with which no man of letters is now unacquainted. It is no lefs entertaining and inftructive to obferve, that even after fome light had been thrown upon the fubject, it required the efforts of ingenious men, for near a century more, to bring the science to its prefent advanced ftate; that, however, fo far from having reached perfection, the myfteries of Nature are fo profound, that there are ftill many defiderata to be known, ftill fufficient to perplex the moft intelligent philofopher, and to induce him to fufpect, while he looks back with the exultation of fuperiority, at the ignorance of the an cients, and even of the illuftrious fages of the feventeenth century, with refpect to the prefent moft obvious principles of the fcience, that we may appear like children to the philofophers of another age, whom new phenomenons, new principles, and perhaps a new theory, may astonish; while, impreffed with a more awful and religious fenfe of the wonderful operations of the Deity, they may exclaim in the language of the celeftial choir," Hallelujah, for the Lord God Omnipotent reigneth". LI. ON THE AURORA BOREALIS, AND OTHER FIERY METEORS. Silent from the north A blaze of meteors fhoots: enfweeping firft THOMSON. THE Aurora Borealis, or Northern Lights, is a kind of meteor appearing in the northern part of the heavens, moftly in the winter time, and in frofty weather. It is now fo generally known, that no defcription is requifite of the appearance which it ufually makes in this country. But it is in the arctic regions that it appears to perfection, particularly during the folftice. In England, the extremities only of thefe northern lights are to be feen, that we have but a faint idea of their splendour and their motions. According to the state of the atmosphere, they differ in colours. They often affume the colour of blood, and make a very dreadful appearance. The ruftic fages become prophetic, and terrify the gazing fpectators with the dread of war, peftilence, and famine. This fuperftition was not peculiar to a Of the Aurora Borealis in Shetland, Siberia, and Hudfon's Bay, and its beneficial effects in the polar regions in general, fee No. V, On Winter in the Polar Regions. By dancing meteors then, that ceafelefs fhake THOMSON, |