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ASTRONOMY and OPTICS. Article 8. Disquisitio, &c. A Dissertation 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 observations made on the comet of 1770 by M. Melier, during four months, were found by M. Eric Prosperin, the Royal Astronomer in Sweden, not to be reconcileable with a parabolic orbit. The latter therefore recommended the investic gation of the true elements of its orbit on the hypothesis of its moving in an ellipsis. This talk has been executed, in the present paper, by M. Lexell; who from his laborious calcula. tions has found reason to conclude, that the period of its revoJution is not more than about five years and seven months : that time agreeing best with the observations. He accounts for its not having since appeared, by observing 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 distance from Jupiter being then only the 58th part of its distance from the sun; and that in the following conjunction, it would be 491 times nearer to Jupiter than to the sun: so that, having regard to their respective masses, the action of Jupiter upon it would be 224 times greater than that of the fun; from which cause a total change in its orbit must ensue. He has nevertheless taken the pains to calculate a table, shewing, 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 supposition that its periodical time is comprised within the limits of five or fix years. Article 11. Observations on the total (with Duration) and an

nular Eclipse of the Sun, taken on the 24th of June 1778, on Board the Espagne, being the Admiral's Ship of the Fleet of New Spain, &c. By Don Antonio Ulloa, F. R. S. Commander of the said Squadron, &c.

Some curious appearances that attended this eclipse deserve to be particularly noticed ; not however without premising that the term annular, used both by Don Ulloa and the tranflator of this Article from the original French, may convey an erroneous idea of the nature of the eclipse, and perplex the reader who has been accustomed to affix a different signification to this term,

The phrase, annular eclipse, has, we apprehend, been hitherto usually, if not solely, applied to those central conjunctions of the sun and moon, in which the apparent diameter of the moon, then in Apogee, is not so great as that of the sun, then in Derigeo : so that in the middle of the eclipse, a portion of the sun's circumference necessarily remains visible, in the form of a luminous ring. To observe such an eclipse, which was visible

in the northern parts of this island, on July 14, 1748, M. Monnier visited Scotland; and Mr. Short gave an account of his and the Earl of Morton's observations upon it, in the Philosophical Transactions, [See Martyn's Abridgment, vol. X. pag. 69] to which we shall have occasion soon to refer.

The circumstances of the present eclipse were directly contrary to those in the preceding case. The moon's apparent diameter was here greater than that of the sun; so 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 circumstance, we suppose, that Don Ulloa has intitled this an annular eclipse : though he speaks of the total obscurity, and determines its duration to have been four minutes.

To explain this matter, it is necessary to observe that, though in the middle of the eclipse, the moon's disk wholly covered that of the sun; so that no part of his body could be visible, by direct rays proceeding from it; and though the darkness was such that some fixed stars were seen; 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 sun and moon, a very brilliant circle of light was observed, surrounding the limb of the moon. Towards the middle of the eclipse, 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 sometimes ex. tended 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 cast: farther off it changed to a pale yellow; which by insensible gradations terminated in a white. A continual rapid whirling motion was perceived in the luminous circle, during nearly the whole time that the sun's body was covered by the moon : but this apparent motion must, we suppose, have been an optical deception.

The above described and other appearances furnith the Author with seemingly just grounds to conclude that they were occasioned by means of an atmosphere surrounding the moon; and which rendered the limb of the sun visible, (though covered by an opaque body) in consequence of its refracting the solar rays: in the same manner-to use a familiar illustration-as a Milling at the bottom of a bason, and concealed from the eye by the sides of it, is instantly rendered visible on pouring in a little water.

Just before the edge of the sun's disk emerged from behind that of the moon, a luminous point was perceived, resembling a far of the second or third magnitude. This appearance was

undoubtedly undoubtedly caused by the sun's light passing through some gulph, or valley in the moon's limb. Such cavities have been observed, during solar eclipses, by other aftronomers; though Don Ulloa declares that it is an extraordinary phenomenon which he was not acquainted with before. In the eclipse, the phenomena of which are described in the volume of the Philosophical Transactions above referred to, similar appearances were observed : and in a late observation of this kind, noticed in our Review, but to which we cannot at present refer, a fimilar appearance in the moon's limb, observed during a folar eclipse, is represented 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 telescope is thus called because it produces two images of a star or other object; one erect, and the other inverted, opposite to each other, and exactly of the same fize; one of which enters the right side of the field, while the other enters the left. The first contact of the edges of the two images gives the passage of the star's preceding Jimb : the coincidence of their centers, when the images accurately cover each other, gives the passage of the centre ; wbich is not otherwise to be obtained in a direct manner : and the last 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 fars; as in this construccion seeing the threads is not required.

In Article 16 are communicated some astronomical observations 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

Eletricity. By Anthony. Fothergill, M. D. F.R.S. at Northampton.

The case of the female patient, whose recovery from a korrible and obftinate disease is the subject of this article, does great credit to the medical powers of electricity. She had first been Leized with those spasmodic contractions of the muscles, or involuntary gesticulations, that distinguish the St. Vitus's Dance. The disease gaining ground was attended with convulsions, so 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 these violent convulsions, he was admitted, as an out-patient, at the Northampton hos



pital. Here the usual 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 concisely described, and the result, will be best given in Mr. Underwood's own words.

July 5. On the glass-footed stool for thirty minutes : sparks were drawn from the arms, neck, and head, which caused a considerable perspiration; and a ralh appeared in her forehead. She then received shocks through her hands, arms, breast, and back; and from this time [quære, this day?] the symptoms abated, her arms beginning to recover their uses.'— The coated bottle held near a quart.

July 13. On the glass-footed stool forty-five minutes :: received strong shocks through her legs and feet, which, from that time, began to recover their wonted uses; also four strong Thocks through the jaws, soon after which her speech returned.

* July 23. On the glass-footed ftool for the space of one hour: sparks were drawn from her arms, legs, head, and breast, which for the first time the very senfibly felt; also owo shocks through the spine. She could now walk alone; her countenance became more florid, and all her faculties seemed wonderfully strengthened ; and from this time the continued mending to a state of perfect health.

• Every time she was electrified, positively, her pulse quickened to a great degree ; and an eruption, much like the itch, appeared in all her joints.'

We are not told whether she was ever electrified in the intervals between these 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 so 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 Chester, 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 success which attended it. The case before us appears to have been replete with difficulties ; nevertheless, three months after the operation, Mr. Orred describes his patient as capable of raising his arm a little from his body (though the callus was still soft) and enjoying the perfect fexure and use of his fore-arm,


Article 6. Account of an extraordinary dropsical Cafe. By Mr.

John Latham. We do not suppose there is any case extant in the records of medicine, in which the operation of tapping had been lo many times performed on one subject, as in the instance 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 necessary 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; so that the whole quantity amounted to 3720 pints, or 465 gallons, that is, near seven hogsheads and a half. It is remarkable, that during the whole time the generally had a good appetite, and was very chearful; visiting her friends at several miles distance, except a day before and after each operation. The original complaint appears to have been an obstruction in one of the ovaria.

CнE м I s тк Ү. Article 3. Experiments on some Mineral Substances. By Peter

Woulfe, F.R.S. This paper

contains some curious chemical observations and experiments, made to discover the constituent parts of various mineral bodies. The Author particularly treats---of crystal, quartz, and fint ;-of a cryftal in Dr. Hunter's museum, which has been partly changed into selenetical spar;-on some mineral substances that contain the earth of alum ;-on feld spar, which, from the observations of the Honourable Mr. Greville, is supposed to owe its origin to clay; and from which, accordingly, Mr. Woulfe has procured a notable quantity of alum ;-of fhirl, jasper, tin spar, and a particular set of spars in the museum of Dr. Hunter, the properties of which were not hitherto known.

In the first class of these experiments, the Author shews, that neither crystal, quartz, or fint, contain the earth of alum; though M. Baumé has asserted, that he obtained alum from each of them, by separately forming with them a liquor filicum after fufing them with fixed alcali; precipitating the earths respectively with an acid, and then dissolving each earth in vitriolic acid; from which solution he obtained real alum. Mr. Woulfe afferts, that by this treatment he never could obtain a grain of alum from any of these substances; but in its room procured a selenite ; which proves, that the bafis of these sub. Hances is not an earth of alum, but a calcareous earth. He


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