TEJA fteel, a change which might probably be brought about by lightning, or other natural agents. In the course of the above trials, Mr. Cavallo obferved, that while the pieces of fteel were red hot, they did not feem to be attracted by the magnet; for the leaft fhock, even pouring the water on them, would remove them from the proper fituation. From several experiments, made in confequence of this obfervation, it appeared, that while iron or steel continue fully red hot, the magnet has no fenfible action upon them; that when fuch a degree of redness, as is clearly perceivable in day-light, begins to disappear, the attraction begins to take place again; and that when cooled a little below the degree of rednefs vifible in the dark, it is as ftrong as ever. He takes notice of two fources of error, by which Kircher and others may have been deceived when they found fmall pieces of iron to be attracted in a red hot as eafily as in a cold state: one is, that if only a part of the mafs be below redness, the magnet will attract the whole, in virtue of that part; the other, that when a small piece is touched by the magnet, the part in contact is immediately cooled fufficiently for attraction to take place. That magnets made hot have less power than when cold, was a discovery of Mr. Canton's. Mr. Cavallo has added to it, that though heated only by boiling water, they do not recover when cold the full power which they had before, neither affecting the needle fo ftrongly, nor lifting fo great a weight of iron; but that iron, heated to the fame degree, affects the needle equally as in its cold ftate. It may be worth trying, whether the magnetilm will be totally deftroyed by repetitions or long continuance of the boiling heat; and increafed, temporarily or permanently, by intenfe cold. The decompofition or dephlogistication of iron by acids or by fire, is known to diminish its attraction to the magnet. Mr. Cavallo has obferved a fingular phenomenon in his experiments on this fubject, that during the effervefcence of iron with the vitriolic and nitrous acids, its action on the needle is increafed. Aftrong effervefcence feems neceffary for this increase; for the marine acid, producing little effervefcence, has no effect of this kind. The Author endeavours to apply thefe experiments toward accounting for the pariation of the magnetic needle, and thinks he has difcovered in them an eafy folution of that wonderful phenomenon. Indeed if the direction of the needle depends upon the attraction of magnetic or ferrugineous bodies in different parts of the earth's furface, a diminution or increase of that attraction, on one fide of the meridian more than on the other, will neceffarily occafion a variation in the needle's direction; and on this principle, the diurnal variations, or the fmall differences obferved in the direction at different times of one day, have been attributed A a 4 by by Mr. Canton to the fun's heat, acting on one fide of the me ridian during one half of the day, and on the other fide during the other half. So far the theory appears confiftent, and the cause adequate to the effect; but with regard to the annual variation, which is the prefent object, we apprehend the cafe is otherwife; and the Author feems to have overlooked the most interefting part of the phenomenon, its regularity. That large maffes of ferrugineous matter, phlogifticated or dephlogifticated by volcanoes, or removed from their original fituation by earthquakes, may affect the needle in particular places, we can readily conceive; and that the Aurora Borealis does affect it, is matter of obfervation. But thefe, which are all the caufes he affigns, are fortuitous, and can produce only irregular fits of variation in the places where they operate; whereas the needle deviates from the meridian by equal fpaces annually, going and returning, with fo much uniformity, that fome have thought its motions reducible to calculation, like those of the planets, and have even constructed tables for that purpose. An Account of a Thunder-form in Scotland (July 19, 1785), with fome Meteorological Obfervations. By Patrick Brydone, Efq. F. R. S. Remarks on Mr. Brydone's Account of a remarkable Thunder-florm in Scotland. By the Right Honourable Charles Earl Stanhope, F. R. S. The remarkable circumftance in this form is, that while the thunder was apparently at a great distance, while Mr. Brydone was counting 25 and 30 feconds between the flashes and reports, and affuring his company (as the prefent theory authorized him to do) that there could be no danger; there happened fuddenly a near and loud clap, neither preceded nor accompanied by any flash it refembled the firing of feveral mufkets fo close together that the ear could hardly feparate the founds, and was not followed by any rumbling noife like the other claps. At a little diftance from Mr. Brydone's houfe, near Coldftream, two loaded carts had juft forded the Tweed, and almost gained the top of an afcent 65 or 70 feet above the bed of the river. The drivers, each fitting upon the fore part of his cart, were difcourfing about the thunder which they heard at a diftance, and wifhing it might be accompanied by a fall of rain; when the foremost, a little more elevated in fituation than the other, was inftantaneously ftruck dead, as were the horses, full in the fight of his companion, who was ftunned by the loudness of the clap, but felt no fhock, nor faw any appearance of lightning or fire whatever. Mr. Brydone has given an excellent defcription (fuch as might be expected from a well-informed philofopher, but which cannot be abridged) of all the particulars which he could obferve or collect, relative to the appearances on the body of the young man, man, on the horses and cart, and on the ground; with an account of fome other effects, inferior in degree, produced by the fame clap. Thefe facts, as Lord Stanhope obferves in the fecond of the papers mentioned at the head of this article, are abfolutely inexplicable by the principles of electricity commonly received. They cannot be attributed to any main firoke of explosion, either direct or tranfmitted, as no lightning paffed from the clouds to the earth, or from the earth to the clouds; nor to any lateral frake, for where there is no main ftroke, no lateral one can exift. His Lordship accounts for them, and in our opinion very fatisfactorily, by that particular species of electric fhock which, in a former work, he has diftinguished by the appellation of the electrical returning ftroke; and although, when he wrote that treatife, he had it not in his power to produce any inftance of perfons killed in this peculiar manner, he ventured to affert with confidence, that, in fuch circumftances as appear, in the prefent cafe, actually to have taken place, fuch an effect would be produced. We fhall endeavour to give our Readers an idea of his Lordship's theory, in the shorteft compass we can, and without reference to the former work, though not without recommending it to the attentive perufal of those who are not yet acquainted with it. Suppofe a cloud (or an affemblage of connected clouds) to be extended horizontally feveral miles in length; with another cloud under it at the hither end; and under this laft, a man ftanding upon a little eminence on the earth. The clouds being fuppofed electrified (pofitively for inftance), and the man being fuppofed within the influence of the electric atmosphere of the lower cloud; the electric fluid naturally belonging to him will neceffarily, by the elaftic electrical preffure of that atmosphere, be forced down into the common stock in the earth. If now the upper cloud, at its further extremity, approaches to the earth within the ftriking diftance, and difcharges its fire, that explofion, to fpectators fituated near the hither end, will be diftant thunder and lightning: but the lower cloud, at the fame inftant, difcharging its fire into the upper, the report only of this explofion will be perceived, the interpofition of the opake cloud preventing the Aafh from being visible on the earth. The electric atmosphere of the cloud being thus fuddenly removed, the electric fluid which had, by the preffure of that atmosphere, been forced out from the man, will fuddenly return into him from the earth, with a velocity, and confequently with a force, which the Author fhews to be fully adequate to the production of the ef Principles of Electricity, &c. by Charles Vifcount Mahon; published in 1779. fects fects in question. He confiders the feveral particular effecs mentioned by Mr. Brydone, and finds them perfectly confiftent with, or rather naturally to point out, this theory; for there are plain marks of the paffage of the electric fluid, from the earth, into the bodies that were affected by it; without any appearance of its having paffed out of them, or been communicated from them to any other body. Some Account of an Earthquake felt in the northern Part of England. By Samuel More, Esq. This earthquake happened on the 11th of Auguft 1786, about 2 o'clock in the morning. Penrith is the northernmost, and Lancafter the fouthernmoft place where it is here mentioned to have been felt; and it would feem that its greateft force was about Amblefide, Cartmeal, and the adjacent and intermediate places, including a confiderable space nearly in the middle between the two first mentioned, Several perfons were awakened by it, and defcribe it as shaking violently the beds, chairs, &c.; but it does not appear that any damage was done. One perfon, who had been awake fome time before the fhock, heard first a rumbling noife, like that of a carriage at a distance, which continued fome time after the fhock was over; he thinks the whole might last four or five feconds. Mr. More was then on a journey in that part of the country, and the particulars mentioned in this paper are those which he collected at the places he paffed through. The fhock appears, however, to have extended much further North, along the weftern coast of the island; and Mr. Brydone, in a poftfcript to his above account of the thunder-ftorm, mentions its being felt pretty feverely about Coldftream in Berwickshire. He was himfelf awaked by it, and felt the motion moft diftinctly, for four or five feconds at leaft, as if the bed had been pulled gently from fide to fide feveral times. The windows were violently fhaken, and made a great noise, which seems to have been mistaken by many people for a noife accompanying the earthquake. It was a dead calm at the time, the morning clofe and warm, and fo dark that, though the moon was but two days paft the full, he could not diftinguifh the hour on his watch, without ftriking a light. An Account of three Volcanos in the Moon. By William Herfchel, LL. D. F. R. S. The existence of volcanos in the moon is the more worthy of attention, as it affords a ftrong evidence of her fimilarity, in the nature and properties of the fubftances of which she is compofed, to our own earth; nor has any celestial phenomenon been hitherto obferved, that points out fo clearly an analogy of this kind. The volcanos which are the fubjects of the prefent Paper, were obferved by Dr. Herschel on the 19th and 20th of April laft laft. Two of them were either nearly extinct, or in a state of going to break out again. The third fhewed an actual eruption of fire or luminous matter; and this burning matter was computed to be above three miles in diameter. Its appearance exactly resembled a small piece of burning charcoal when it is covered by a very thin coat of white afhes, fuch as frequently adheres to it when it has been fometime ignited; and its brightnefs was about as ftrong as fuch a coal would be seen to glow with it in faint day-light. All the adjacent parts of the volcanic mountain feemed to be faintly illuminated by the eruption, and were gradually more obfcure as they lay at a greater diftance from the crater. Defcription of a Set of Halos and Parhelia, feen in the Year 1771, in North America. By Alexander Baxter, Efq. This fingular phenomenon was obferved at Fort Gloucester, on the river of Lake Superior, on the 22d of January 17715 from a little before to half an hour after two in the afternoon; the fun being then a little more than one-third way from the horizon to the zenith. A very large halo, or luminous circle, furrounded the fun; and, at the fame elevation with him, a beautifully enlightened circle, parallel to the horizon, extended quite round, till the two extremities of it terminated in the halo: at the points of interfection, two parhelia, or mock-funs, were formed, fo like the true fun, that through a hazy sky they might have been mistaken for him. Oppofite to the fun was a lumimous cross, in the fhape of a St. Andrew's crofs, cutting, at its point of interfection, the horizontal circle, and there forming another parhelion. In the middle points between this parhelion and the two former were two others; in all five, in the fame horizontal circle, and at equal diftances from one another. There was alfo, very near the zenith, a rainbow, of very bright and beautiful colours, fomewhat lefs than a femicircle, with the convex fide towards the fun. Mr. Baxter has accompanied his defcription with a drawing, in which all these appearances are very diftinctly represented. Account of the Strata obferved in finking for Water at Bofton in Lincolnshire. By Mr. James Limbird, Surveyor to the Corpora tion. A well had been funk in the market-place at Bofton, to the depth of 186 feet; but no water being met with, the corporation employed a well-borer, George Nailor, to fink farther, and this Paper gives an account of the thickneffes, or depths from the furface, of the different beds of earth through which George Nailor bored. It would feem that, down to the depth of 444 feet, almoft the whole mafs is clay, light blue near the furface, and dark blue further down, interfected by a few thin strata of fand and gravel, and of a stone like ragftone, with one ftratum of |