ASTRONOMY and OPTICS. Article 8. Difquifitio, &c. A Differtation on the periodical Time of the Comet which appeared in the Year 1770. By J. A. Lexell, Member of the Academy of Sciences at Petersburgh. The obfervations made on the comet of 1770 by M. Meffier, during four months, were found by M. Eric Profperin, the Royal Aftronomer in Sweden, not to be reconcileable with a parabolic orbit. The latter therefore recommended the investigation of the true elements of its orbit on the hypothesis of its moving in an ellipfis. This talk has been executed, in the prefent paper, by M. Lexell; who from his laborious calculations has found reafon to conclude, that the period of its revolution is not more than about five years and seven months: that time agreeing beft with the obfervations. He accounts for its not having fince appeared, by obferving that its orbit must probably have been affected or altered by the attraction of Jupiter; with which planet he finds that it must have been in conjunction on May 27, 1767: its diftance from Jupiter being then only the 58th part of its diftance from the fun; and that in the following conjunction, it would be 491 times nearer to Jupiter than to the fun: fo that, having regard to their respective maffes, the action of Jupiter upon it would be 224 times greater than that of the fun; from which caufe a total change in its' orbit must ensue. He has nevertheless taken the pains to calculate a table, fhewing, for every month in the year, in what part of the heavens this quick-revolving or Mercurial comet is to be looked for; on the fuppofition that its periodical time is comprised within the limits of five or fix years. Article 11. Obfervations on the total (with Duration) and annular Eclipfe of the Sun, taken on the 24th of June 1778, on Board the Efpagne, being the Admiral's Ship of the Fleet of New Spain, &c. By Don Antonio Ulloa, F. R. S. Commander of the faid Squadron, &c. Some curious appearances that attended this eclipse deserve to be particularly noticed; not however without premifing that the term annular, ufed both by Don Ulloa and the tranflator of this Article from the original French, may convey an erroneous idea of the nature of the eclipfe, and perplex the reader who has been accustomed to affix a different fignification to this term. The phrafe, annular eclipfe, has, we apprehend, been hitherto ufually, if not folely, applied to thofe central conjunctions of the fun and moon, in which the apparent diameter of the moon, then in Apogao, is not fo great as that of the fun, then in Perigao: fo that in the middle of the eclipfe, a portion of the fun's circumference neceffarily remains vifible, in the form of a luminous ring. To obferve fuch an eclipfe, which was visible in the northern parts of this ifland, on July 14, 1748, M. Monnier vifited Scotland; and Mr. Short gave an account of his and the Earl of Morton's obfervations upon it, in the Philofophical Tranfactions, [See Martyn's Abridgment, vol. x. pag. 69] to which we fhall have occafion foon to refer. The circumftances of the prefent eclipfe were directly contrary to those in the preceding cafe. The moon's apparent diameter was here greater than that of the fun; fo that the moon more than covered his body, and yet did not wholly conceal it: which is indeed the principal fingularity that attended this phenomenon. It is on account of this circumftance, we fuppofe, that Don Ulloa has intitled this an annular eclipfe: though he fpeaks of the total obfcurity, and determines its duration to have been four minutes. To explain this matter, it is necessary to obferve that, though in the middle of the eclipfe, the moon's difk wholly covered that of the fun; fo that no part of his body could be visible, by direct rays proceeding from it: and though the darkness was fuch that fome fixed ftars were feen; and the fowls on board the ship went to rooft, as if it had been night: yet at this very time, and for a minute or two before and after the coincidence, or nearest approach, of the centers of the fun and moon, a very brilliant circle of light was observed, furrounding the limb of the moon. Towards the middle of the eclipfe, this light was about the breadth of a fixth part of the moon's diameter and even from the circumference of this luminous circle, there darted forth, at intervals, weaker rays of light; which fometimes extended to the distance of a diameter of the moon. That part of the light, which was contiguous to the moon's limb, had a reddish caft: farther off it changed to a pale yellow; which by infenfible gradations terminated in a white. A continual rapid whirling motion was perceived in the luminous circle, during nearly the whole time that the fun's body was covered by the moon but this apparent motion muft, we fuppose, have been an optical deception. The above defcribed and other appearances furnish the Author with feemingly juft grounds to conclude that they were occafioned by means of an atmosphere furrounding the moon and which rendered the limb of the fun vifible, (though covered by an opaque body) in confequence of its refracting the folar rays in the fame manner-to ufe a familiar illuftration-as a hilling at the bottom of a bafon, and concealed from the eye by the fides of it, is inftantly rendered vifible on pouring in a little water. Juft before the edge of the fun's difk emerged from behind that of the moon, a luminous point was perceived, refembling aftar of the fecond or third magnitude. This appearance was undoubtedly undoubtedly caused by the fun's light paffing through some gulph or valley in the moon's limb. Such cavities have been obferved, during folar eclipfes, by other aftronomers; though Don Ulloa declares that it is an extraordinary phenomenon which he was not acquainted with before. In the eclipfe, the phenomena of which are defcribed in the volume of the Philofophical Tranfactions above referred to, fimilar appearances were observed: and in a late obfervation of this kind, noticed in our Review, but to which we cannot at prefent refer, a fimilar appearance in the moon's limb, obferved during a folar eclipfe, is reprefented as furnishing a proof that the cavities in the moon, at least those in her limb, do not contain water or any other fluid, Article 13. Account of an Iconantidiptic Telescope, invented by M. Jeaurat, of the Academy of Sciences at Paris. Communicated by J. H. de Magellans, F. R. S. This telefcape is thus called because it produces two images of a star or other object; one erect, and the other inverted, Oppofite to each other, and exactly of the fame fize; one of which enters the right fide of the field, while the other enters the left. The firft contact of the edges of the two images gives the paffage of the ftar's preceding limb: the coincidence of their centers, when the images accurately cover each other, gives the paffage of the centre; which is not otherwife to be obtained in a direct manner: and the laft contact of the edges, when the two images separate, gives the paffage of the following limb. This invention obviates the trouble of illuminating the threads of the telescope, in observing small ftars; as in this conftruction feeing the threads is not required. In Article 16 are communicated fome aftronomical obfervations made at Corke, by J. Longfield, M. D.: and in Article 17, observations made to determine the latitude of Madras, By W. Stephens, Chief Engineer. MEDICINE. Article 1. An Account of a Cure of the St. Vitus's Dance, by Electricity. By Anthony, Fothergill, M. D. F. R. S. at Northampton. The cafe of the female patient, whofe recovery from a horrible and obftinate disease is the subject of this article, does great credit to the medical powers of electricity. She had first been seized with thofe fpafmodic contractions of the mufcles, or involuntary gesticulations, that diftinguish the St. Vitus's Dance. The difeafe gaining ground was attended with convulfions, fo violent as to render it difficult for two affiftants to keep her in bed; and which foon deprived her of speech, and the use of her limbs. After labouring fix weeks under thefe violent convulfions, he was admitted, as an out-patient, at the Northampton hof 6 pital. Here the ufual powers of medicine were ineffectually tried about a month, under the care of Dr. Fothergill; who, as a last resource, recommended a trial of electricity, under the management of the Rev. Mr. Underwood, an ingenious electrician. The whole process, perhaps too concifely defcribed, and the refult, will be beft given in Mr. Underwood's own words. July 5. On the glass-footed ftool for thirty minutes: fparks were drawn from the arms, neck, and head, which caufed a confiderable perfpiration; and a rash appeared in her forehead. She then received fhocks through her hands, arms, breaft, and back; and from this time [quære, this day?] the symptoms abated, her arms beginning to recover their ufes.'-The coated bottle held near a quart. 6 July 13. On the glafs-footed ftool forty-five minutes: received ftrong fhocks through her legs and feet, which, from that time, began to recover their wonted ufes; also four strong fhocks through the jaws, foon after which her fpeech returned. July 23. On the glafs-footed ftool for the fpace of one hour: fparks were drawn from her arms, legs, head, and breaft, which for the first time the very fenfibly felt; also two fhocks through the fpine. She could now walk alone; her countenance became more florid, and all her faculties feemed wonderfully ftrengthened; and from this time fhe continued mending to a state of perfect health. Every time fhe was electrified, pofitively, her pulfe quickened to a great degree; and an eruption, much like the itch, appeared in all her joints.' We are not told whether fhe was ever electrified in the intervals between thefe three days, or how often; or whether nothing more was done than is related in this quotation. At the end of the article, Dr. Fothergill mentions his having cured a boy, by means of electricity, who had long had the St. Vitus's Dance, though not in fo great a degree as the above-mentioned patient. Article 2. A Cafe in which the Head of the Os Humeri was fawn off, &c. By Mr. Daniel Orred, of Chefter, Surgeon, &c. In our xlivth vol. [March 1771, p. 211.] we gave an account of the first operation of this kind, performed by Dr. White, and of the fuccefs which attended it. The cafe before us appears to have been replete with difficulties; nevertheless, three months after the operation, Mr. Orred defcribes his patient as capable of raifing his arm a little from his body (though the callus was ftill foft) and enjoying the perfect flexure and ufe of his fore-arm, Article Article 6. Account of an extraordinary dropfical Cafe. By Mr. John Latham. We do not fuppofe there is any cafe extant in the records of medicine, in which the operation of tapping had been fo many times performed on one fubject, as in the inftance now before us. The patient was a young lady, who was obliged, for the first time, at about the age of nineteen, to submit to that operation in June 1774. In fix weeks it became neceffary to repeat it; and afterwards once a month, to the end of that year. During the whole of the year 1775, Mr. Latham tapped her, on a medium, once in a fortnight: and from that time to the time of her death in May 1778, the generally underwent the operation every eight or nine days. She was tapped 155 times, and, on an average, 24 pints were drawn off at each operation; fo that the whole quantity amounted to 3720 pints, or 465 gallons, that is, near seven hogfheads and a half. It is remarkable, that during the whole time the generally had a good appetite, and was very chearful; vifiting her friends at feveral miles diftance, except a day before and after each operation. The original complaint appears to have been an obstruction in one of the ovaria. CHEMIST K Y. Article 3. Experiments on fome Mineral Subflances. By Peter Woulfe, F. R. S. This paper contains fome curious chemical obfervations and experiments, made to difcover the conftituent parts of various mineral bodies. The Author particularly treats-of cryftal, quartz, and flint ;-of a cryftal in Dr. Hunter's museum, which has been partly changed into felenetical spar;-on fome mineral fubftances that contain the earth of alum ;-on feld fpar, which, from the obfervations of the Honourable Mr. Greville, is fupposed to owe its origin to clay; and from which, accordingly, Mr. Woulfe has procured a notable quantity of alum;-of fhirl, jafper, tin fpar, and a particular fet of spars in the museum of Dr. Hunter, the properties of which were not hitherto known. In the first clafs of thefe experiments, the Author fhews, that neither cryftal, quartz, or flint, contain the earth of alum; though M. Baumé has afferted, that he obtained alum from each of them, by feparately forming with them a liquor filicum after fufing them with fixed alcali; precipitating the earths refpectively with an acid, and then diffolving each earth in vitriolic acid; from which folution he obtained real alum. Mr. Woulfe afferts, that by this treatment he never could obtain a grain of alum from any of thefe fubftances; but in its room procured a felenite; which proves, that the bafis of these sub#tances is not an earth of alum, but a calcareous earth. He afcribes |