to the author of this article, to have made one fuppofition the foundation of another, and that of others, in order to attain probability, which is the utmost we can expect, when we are reafoning upon bodies too remote for even an apparent diameter. Mr. Mitchell obferves, < The very great number of stars that have been discovered to be double, triple, &c. particularly by Mr. Herschel, if we apply the doctrine of chances, as I have heretofore done in my "Enquiry into the probable Parallax, of the Fixed Stars," published in the Philofophical Tranfactions for the year 1767, cannot leave a doubt with any one, who is properly aware of the force of thofe arguments, that by far the greatest part, if not all of them, are fyftems of ftars fo near to each other, as probably to be liable to be affected fenfibly by their mutual gravitation; and it is therefore not unlikely, that the periods of the revolutions of fome of thefe about their principals (the fmaller ones being, upon this hypothefis, to be confidered as fatellites to the others) may fome time or other be difcovered.' It was neceffary to quote this paffage particularly, fince it is the first time we recollect any of the fixed stars to have been confidered as fatellites. The author is fufficiently aware of the length of time requifite either to confute or establish this idea. He proposes to measure the distance, density, and magnitude of thefe bodies by the diminution of the velocity of light, if light be under the laws of gravitation. We shall felect his own words. The diminution of the velocity of light, in cafe it should be found to take place in any of the fixed stars, is the principal phænomenon whence it is propofed to difcover their distance, &c. Now the means by which we may find what this diminution amounts to, feems to be fupplied by the difference which would be occafioned in confequence of it, in the refrangibility of the light, whofe velocity fhould be fo diminished. For let us fuppofe with fir Ifaac Newton (fee his Optics, prop. vi. par. 4 and 5.) that the refraction of light is occafioned by a certain force impelling it towards the refracting medium, an hypothefis which perfectly accounts for all the appearances. Upon this hypothefis the velocity of light in any medium, in whatever direction it falls upon it, will always bear a given ratio to the velocity it had before it fell upon it; and the fines of incidence and refraction will, in confequence of this, bear the fame ratio to each other with thefe velocities inversely. Thus, according to this hypothefis, if the fines of the angles. of incidence and refraction, when light paffes out of air into glafs, are in the ratio of 31 to 20, the velocity of light in the glafs must be to its velocity in air in the fame proportion of 31 to 20. But because the areas reprefenting the forces generating thefe velocities, are as the fquares of the velocities, thefe areas must be to each other as 961 to 400. And if 400 reprefents the area which correfponds to the force producing the ori ginal velocity of light, 561, the difference between 961 and 400, must reprefent the area correfponding to the additional force, by which the light was accelerated at the furface of the glafs.' Mr. Mitchell imagines alfo, that a prifm, with a small refracting angle, would be a convenient inftrument to measure the difference of the velocity of light. We are furprised that he has not himself tried the experiment, as the inftrument is fo eafily procured. The whole paper is ingenious, and will probably be found to deserve attention. Art. VIII. A Meteorological Journal for the Year 1782, kept at Minehead, in Somersetshire. By Mr. John Atkins.Meteorological journals are of confiderable utility, when connected with the prevailing epidemics; but, independent of them, are folitary detached facts of curiosity rather than advantage. This diary is, in our opinion, unneceffarily minute; and from the fudden changes in the thermometer, we strongly fufpect that this inftrument is affected by the reflection of the fun, though not exposed to its direct beams. Few are aware by what inconfiderable caufes a nice thermometer is influenced. The rain, during the year, at Minehead, was in 1782, 31.26 inches; and this quantity is feldom exceeded, even in the fituations moft fubject to rain. Art. IX. Defcription of a Meteor, obferved August 18, 1783, By Mr. Tiberius Cavallo, F. R. S.-Art. X. An Account of the Meteors of the 18th of August and 4th of October, 1783. By Alex. Aubert, Efq. F. R. S.-Art. XI. Obfervations on a remarkable Meteor feen on the 18th of August, 1783. By William Cooper, D. D. F. R. S. Archdeacon of York.-Art. XII. An Account of the Meteor of the 18th of Auguft, 1783. By Richard Lovell Edgeworth, Efq. F. R. S. -Art. XVIII. An Account of fome late fiery Meteors; with Obfervations. By Charles Blagden, M. D. Sec. R. S.We join these different articles, as they relate to the fame or fimilar phænomena; but fhall give a particular account of Dr. Bladgen's obfervations, fince they comprise those of the former articles, as well as many other defcriptions of the fame meteors. The first occurred the 18th of Auguft, about 16 minutes after 9. It feems to have arifen fomewhere in the northern ocean, beyond the extremities of this ifland, and was obferved in the N. N. W. quarter, from whence it proceeded 8. S. E. almost in the direction of the magnetic meridian. When When it was nearly over Lincolnshire, it feemed to deviate, in its course, more towards the eaft; and this deviation was marked by two loud reports, defcribed by Dr. Cooper near Stockton, each as equal to that of a nine-pounder, and pretty' diftinctly heard at Windfor, by Mr. Cavallo. At this time too, the ball feemed to burst into many fmaller ones; but foon refuming its original courfe and appearance, paffed the Straits, of Dover, and was probably feen as far as Rome. It seems to have extended its courfe above one thousand miles, and not to have been lefs than fifty-five miles above the surface of the earth its tranfverfe diameter was probably near half a mile ;' and its real elongation behind, for the apparent length of train was delufive, feems feldom to have exceeded twice or thrice its real tranfverfe diameter: its velocity was aftonishing, for it probably exceeded twenty miles in a fecond. This is a fhort account of the refult of various obfervations; we are obliged to omit Dr. Blagden's reasoning, but we are fatisfied that his computations are within the truth. The fecond meteor appeared the 4th of October, at 43' past 6 in the evening. Its direction was nearly the fame as that of the first, and the height seems not to have been lefs; but its duration was fo tranfitory, that few obfervations were made on it. Dr. Blagden then proceeds to fome general remarks on the nature of these surprising bodies, which feem almost to realife Buffon's vifionary fyftem, of pieces ftruck from the fun, whirled with endless violence o'er the pendant world,' till, their projectile force diminishing, they yield to the attractive power of fome other fun, and become sober planets, and new worlds. But many will think, with our author, that this fanciful hypothefis fcarcely deferves attention. Dr. Blagden has not even condefcended to mention it in his enumeration of the different opinions relating to the cause of thefe or fimilar meteors. He is inclined to think them of an electrical nature; or perhaps, an accumulated light, of the fame kind with that which darts and plays in the aurora borealis. The hiffing noise, which some obfervers defcribe, when the meteor passes near them, is felt in northern countries on the appearance of thefe lights; and their direction in the magnetical meridian fupports the analogy. We shall extract the following quotation from profeffor Gmelin, on account of its curiofity, though we think, with Dr. Blagden, that the appearances are exagge rated. "These northern lights begin with fingle bright pillars, rif ing in the N. and almoft at the fame time in the N. E. which gradually increasing, comprehends a large space of the heavens, M 3 ryth rush about from place to place with incredible velocity, and finally almoft cover the whole fky up to the zenith. The streams: are then feen meeting together in the zenith, and produce an appearance as if a valt tent was expanded in the heavens, glit tering with gold, rubies, and fapphire. A more beautiful, fpectacle cannot be painted; but whoever fhould fee fuch a northern light for the first time, could not behold it without terror. For however fine the illumination might be, it is attended, as I have learned from the relation of many perfons, with fuch a hiffing, cracking, and rufhing noife throughout the air, as if the largeft fire-works were playing off. To defcribe what they then hear, they make ufe of the expreffion Spolochi chodjat, that is, the raging host is paffing. The hunters who purfue the white and blue foxes in the confines of the Icy fea, are often overtaken in their courfe by these northern lights.. Their dogs are then fo much frightened, that they will not move, but lie obftinately on the ground till the noife has paffed. Commonly clear and calm weather follows this kind of northern lights. I have heard this account, not from one perfon only, but confirmed by the uniform teftimony of many, who have fpent part of feveral years in thefe very northern regions, and inhabited different countries from the Yenifei to the Lena; so that no doubt of its truth can remain. This feems indeed to be the real birth-place of the aurora borealis." Our author does not imagine that the meteor's direction is influenced by magnetifm; but that the direction of the magnetic power is produced by the accumulation of the electric fluid, in the N. N. W. quarter. This is indeed the center of the aurora borealis; for, though we have feen it in many different quarters, yet it fcarcely ever appears in the S. S. E. We have seen every point of the compafs illuminated at one time, except this; and we have never feen it enlightened at the fame time with the North. Thofe will understand this variety, who attend to the different ftates of pofitive and negative electricity; or who recollect, that fome meteors proceed from the fouth, though they ftill continue in the magnetic meridian. Art. XVII. On a Method of defcribing the relative Pofition and Magnitudes of the Fixed Stars; together with some Aftronomical Obfervations. By the Rev. Francis Wollafton, LL. B. F. R. S.-As fo many changes have occurred in the appearances of the fixed ftars, Mr. Wollafton propofes, that aftronomers fhould examine their prefent appearance with accuracy, and form a more exact celeftial atlas than has yet been publifhed. To a night-glafs of Dolland's conftruction, which magnifies about fix times, and takes in as many degrees of a great circle, Mr. Wollafton has added four wires, croffing each other in the centre. By this means any ftar may be brought to to the centre, and the relative fituation of the furrounding ones easily sketched on a card, and their places are afterwards to be reduced to the general atlas. If the fituation of any ftar is doubtful, it may be brought to the centre, and its place more exactly ascertained. After the principal tars are thus marked, the plan may be filled up by ufing glaffes of a greater power, and fixing the fituation of fmaller ftars: the whole atlas may, in Mr. Wollaton's opinion, be foon completed, if aftronomers will divide the heavens into particular districts, and each confine himself to one. The paper is concluded with an account of different aftronomical obfervations. The only remaining articles of this volume relate to Mr. Cavendish's experiments on air, and the controverfy which they have occafioned between him and Mr. Kirwan; but, as we wish to examine the fubject with care, we must delay our account of it till the appearance of our next Number. A Syftem of Surgery. By Benjamin Bell, Member of the Royal College of Surgeons, one of the Surgeons to the Royal Infirmary, and Fellow of the Royal Society of Edinburgh. Illuftrated with Copper-plates. Vol. III. 8vo. 6s. in Boards. Ro binfon. IN N the Fifty-fifth and Fifty-feventh Volumes we have carefully examined the former parts of this work, and, on that account, may be now more concife. The third volume contains the chirurgical treatment of affections of the brain from violence, and difeafes of the eye. It is diftinguished by the fame clearness and accuracy which we have already mentioned, and it is extended with the fame minutenefs: a minutenefs which may be neceffary to young practitioners, and on fubjects of importance, but which is feldom agreeable to proficients. In trepanning, Mr. Bell recommends the trepan, in preference to the trephine. He difapproves of removing a large portion of the scalp, but advises the practitioner to raise it in the ufual manner; and, if neceffary, to cut off the corners.' We look on it as a material improvement in modern practice, that every portion of the fcalp, except what may be injured by the contufion, is preferved and united by the first intention." Mr. Bell's fagacity has difcovered the utility of this method in general; and we now only plead in favour of the little angles. Our author thinks that a contra-fiffure may easily occur, and that even the internal table may be fractured, while no fracture appears on the external furface. A fhock will certainly fometimes break a more thin brittle fubftance, when M 4 con |