Philosophical transactions, Vol. L. Part I. For the year 1757. · Various
TAB. XVI.
_Fig._ 1. _An Euonymi species?_ If this be an Euonymus, it is not so far advanced as to form the seeds: and is therefore to be considered only in its progress from the flower towards seeding: which is the case in several of these, whose calyces appear still upon them, and hinder us from absolutely determining what they are. _Fig._ 2. A berry of the Sapindus, or Soap-tree, of America, being not at all deformed, only having a little lump of pyrites upon it: but there is another quite free. _Fig._ 3. _Huræ Germen._ This is undoubtedly the young Sand-box, or fruit of the Hura, so well known for its beautiful form to the curious, who collect specimens of natural history; and seems to shew the time of the deluge. _Fig._ 4. This, I think, is certainly the stone of an eastern Mango; such as comes over to us pickled, and, the stone being opened on one side, is generally stuffed with spices. _Fig._ 5. _Euonymi latifolii species._ This is a large species of Euonymus, perhaps of Clusius. _Fig._ 6. This body seems to be a Milleped, or Wood-louse. It is turned round, the two extremities meeting; which is the attitude assumed by these animals, upon being in any-wise obstructed in their passage, or handled. _Fig._ 7. A small long Bean, like our horse-bean; but longer than any we have in England.
_Fig._ 8. Unknown to me. _Fig._ 9. A species of Horse-chesnut from America. _Fig._ 10. The external husk of the fruit of the Sapindus, or Soap-tree. _Fig._ 11. I cannot determine whether this be an Olive, or the yellow Myrobalan; but believe it the Myrobalan. _Fig._ 12. _A Palmæ species?_ It seems a small Palma-coco. _Fig._ 13, 14. unknown, as well as _fig._ 15. _Fig._ 16. Unknown. The reason of the four last being not to be distinguished is, that they seem to be the buds of their several species, before they were perfectly formed. So that while some of the antediluvian productions are mature, others appear to be premature; and consequently one would be inclined to think them the inhabitants of places of different latitudes. _Fig._ 17. A species of foreign Walnut, injured and compressed. _Fig._ 18. A Plumb-stone. _Fig._ 19. The claw of an American Crab; which, being on the opposite side of the mass containing the body, could not come in view with it at the same time. _Fig._ 20. The body of the crab, with other parts, appearing thro’ the stony matter that invelopes it, which appears to be an induration of yellow clay. _Fig._ 21. seems a long American Phaseolus. Part of the petrified husk is upon it. _Fig._ 22. An American Echinite of the flat kind, much resembling that species which Rumphius calls _Echinus sulcatus primus_.
_Fig._ 23. _Arista cujusdam Graminis._ This body has all the characteristics of an ear of corn, or some species of grass, of which there are many. This has been taken for a spine of an Echinus: but, as we are to consider its nearest resemblance to whatsoever body, we must conclude it as we have said. I never saw any spine in the least like it; but an ear of corn, ripe and dry, is as susceptible of being petrified, as a crustaceous animal, in every respect. Indeed the spiculæ of the ear, each arising from the grain, being very slender, are of course destroyed during the petrifaction; but the form of the ear is actually preserved, as much as the nature and circumstances of the thing will allow. _Fig. a._ A manifest species of Pediculus Marinus crumped up. _b._ A Seed-vessel, given me by Mr. Da Costa, found in a clay-pit in Staffordshire. _c._ Cocculus Indicus. LII. _Observations upon the Comet that appeared in the Months of_ September _and_ October _1757, made at the Royal Observatory by_ Ja. Bradley, _D.D. Astronomer Royal, F.R.S. and Member of the Royal Academy of Sciences at_ Paris. [Read Dec. 22, 1757.] I Deferred to give an account of my observations upon the Comet that hath lately appeared, till I could settle the places of the stars with which it had been compared; several of them not being inserted in the British catalogue, and those which are, requiring some small corrections, which I have since made from my own observations.
When I first discovered this Comet, it appeared to the naked eye like a dull star of the 5th or 6th magnitude; but viewing it thro’ a seven-foot Telescope, I could perceive a small Nucleus (surrounded, as usual, with a nebulous atmosphere), and a short tail extended in a direction opposite to the sun. Some small stars then appearing in the field of the telescope with the Comet, I measured its distance from them with a Micrometer; and on September 12ᵈ at 16ʰ 2’ mean time, I found it to be 1° 13’ 5" distant from a small star, whose right ascension was afterwards found to be 89° 49’ 40" and declination 36° 11’ 30" north: and near the same time the Comet was observed to be 43’ 10" from another star, whose right ascension was 90° 20’ 0" and declination 35° 12’ 0" north. Hence I collected, that the Comet’s right ascension was 89° 29’ 10“ and its declination 35° 0’ 20" north. September 13ᵈ 12ʰ 37’ mean time (which is likewise made use of in the following observations), the Comet had the same right ascension with a small star, whose right ascension was 93° 5’ 30" and declination 34° 36’ 40" north; and it was about two minutes more northerly than the star. Hence the Comet’s right ascension was 93° 5’ 30" and its declination 34° 38’ 40" north.
September 14ᵈ 14ʰ 0’ the Comet preceded θ Geminorum 1° 31’ 35“ in right ascension, and was 11’ 35" more southerly. The apparent right ascension of θ Geminorum was then 99° 11’ 40“ and its declination 34° 13’ 25" north. Hence the right ascension of the Comet was 97° 40’ 5" and its declination 34° 1’ 50" north. Sept. 17ᵈ 13ʰ 0’ a small star (whose right ascension was 109° 55’ 20“ and declination 31° 27’ 40") preceded the Comet 47’ 10" in right ascension, and was 12’ 30" more northerly. Hence the Comet’s right ascension was 110° 42’ 40" and its declination 31° 15’ 10" north. Sept. 19ᵈ 15ʰ 17’ a star (whose right ascension was 118° 29’ 40" and declination 28° 9’ 45") preceded the Comet 1° 14’ 0" in right ascension, and was more southerly 15’ 45“. Hence the Comet’s right ascension was 119° 43’ 40" and declination 28° 25’ 30" north. Sept. 23ᵈ 15ʰ 57’ a star (whose right ascension was 134° 55’ 45" and declination 22° 15’ 55" north) preceded the Comet 12’ 30" in right ascension, and was 29’ 0" more northerly. Hence the Comet’s right ascension was 135° 8’ 15" and its declination 21° 46’ 55" north. Sept. 24ᵈ 15ʰ 21’ the Comet had the same declination with a small star that preceded it 10’ 15“ in right ascension. This star’s right ascension was afterwards found to be 138° 13’ 45" and its declination 20° 5’ 20". Hence the Comet’s right ascension was 138° 24’ 0" and its declination 20° 5’ 20" north.
Sept. 28ᵈ 16ʰ 22’ the Comet followed Regulus 1° 7’ 12" in right ascension, and was 14’ 45" more northerly. The right ascension of Regulus being then 148° 51’ 13" and its declination 13° 8’ 35" north; the Comet’s right ascension was 149° 58’ 25" and its declination 13° 23’ 20" north. Sept. 30ᵈ 16ʰ 24’ ρ Leonis (whose right ascension was 155° 0’ 10" and declination 10° 32’ 53" north) followed the Comet 18’ 45" in right ascension, and was 7’ 53" more northerly. Hence the Comet’s right ascension was 154° 41’ 25" and its declination 10° 25’ 0" north. October 2ᵈ 16ʰ 48’ the 37th star Sextantis. Hevel. in the British Catalogue (whose right ascension was 158° 21’ 25" and declination 7° 38’ 40" north) preceded the Comet 32’ 50" in right ascension, and was 3’ 20" more southerly. Hence the Comet’s right ascension was 158° 54’ 15" and its declination 7° 42’ 0" north. October 3ᵈ 16ʰ 45’ _c_ Leonis (whose right ascension was 162° 2’ 15’ and declination 7° 24’ 0" north) followed the Comet 1° 12’ 55" in right ascension, and was 56’ 40" more northerly. Hence the Comet’s right ascension was 160° 49’ 20" and its declination 6° 27’ 20" north. October 4ᵈ 17ʰ 0’ _d_ Leonis (whose right ascension was 162° 0’ 15" and declination 4° 54’ 57" north) preceded the Comet 40’ 15” in right ascension, and was more southerly 20’ 53". Hence the Comet’s right ascension was 162° 40’ 30" and its declination 5° 15’ 50" north.
October 7ᵈ 16ʰ 54’ the 79th Leonis in the British Catalogue (whose right ascension was 167° 53’ 37" and declination 2° 44’ 15" north) followed the Comet 13’ 0" in right ascension, and was more northerly 38’ 35". Hence the Comet’s right ascension was 167° 40’ 37" and its declination 2° 5’ 40" north. October 8ᵈ 16ʰ 53’ the Comet preceded _v_ Leonis 1° 53’ 30" in right ascension, and was 37’ 20" more northerly. The right ascension of this star was 171° 7’ 45" and its declination 0° 30’ 55" north; therefore the Comet’s right ascension was 169° 14’ 15" and its declination 1° 8’ 15" north. October 11ᵈ 16ʰ 52’ the Comet followed _v_ Leonis 2° 33’ 30" in right ascension, and appeared 1° 55’ 5" more southerly; but it being near the horizon, the difference of right ascension must have been contracted by refraction about 1’ 5", and the difference of declination about 1’ 30": so that the corrected right ascension of the Comet was 173° 42’ 20" and its declination 1° 25’ 40" south. Immediately after this observation a fog arose, which prevented me from repeating it; and several mornings following proving hazy or cloudy, I could not see the Comet again till October 18th, about an hour and a quarter before sun-rising; when the twilight being strong, and the Comet low, it appeared very faint. However, I was unwilling to omit the opportunity of determining its place, as near as I could, by a single observation, in the following manner.
At 6ʰ 59’ 54" ½ sidereal time, I observed the passage of the Comet over the perpendicular wire of my equatorial Sector; then leaving the instrument in the same position till the next evening, I observed, that at 22ʰ 8’ 15" sidereal time, the 17th star of Eridanus in the British Catalogue passed over the same wire (or horary circle) 9’ 30" more southerly than the Comet. And at 23ʰ 45’ 36" sidereal time the star marked _b_ in Eridanus passed, 19’ 55" more northerly than the Comet. I found that the situation of my instrument was not sensibly altered between the 18th and 19th of October; for the transits and the difference of declination of the same stars being observed with it again on the 19th of October, they agreed very well with those that were taken the preceding night. It may therefore be supposed, that the position of the instrument continued the same likewise during the time of the foregoing observations. The right ascension of the 17th star of Eridanus being 49° 39’ 10" and its declination 5° 55’ 25" south; and the right ascension of _b_ of Eridanus being 73° 59’ 15" and its declination 5° 25’ 10" south; I collected, that when the Comet passed the wire (or horary circle) which was October 17ᵈ 17ʰ 12’ mean time, its right ascension was 182° 34’ 0" and its declination 5° 45’ 35" south.
The last time that I saw the Comet was on the 19th of October in the morning; but it then appeared so faint, that I could not observe its place. Its elongation from the sun was then but about 20 degrees; and from that day to the present it hath always been less; which is the principal reason why it was invisible to us at the time when it was in its perihelion, and hath remained so ever since. The elongation will indeed soon become greater, and yet it is probable that we shall not be able to see the Comet again; because its real distance from the sun will be greater than it was when I first saw it, and it will be also four times further from us than it was at that time. The Comet kept nearly at the same distance from the earth for ten or twelve days together after I first saw it; but its brightness gradually increased then, because it was going nearer to the sun. Afterwards, when its distance from the earth increased, altho’ it continued to approach the sun, yet its lustre never much exceeded that of stars of the second magnitude, and the tail was scarce to be discerned by the naked eye. All the forementioned observations were made with a Micrometer in a seven-foot Tube, excepting those of the 3d, 11th, and 17th days of October, which were taken with a curious Sector constructed for such purposes by the late ingenious Mr. George Graham; of which Dr. Smith has given a very exact description in his third book of Optics.
Supposing the Trajectory of this Comet to be parabolic, I collected from the foregoing observations, that its motion round the sun is _direct_, and that it was in its _perihelion_ October the 21st, at 7ʰ 55’ mean (or equated) time at Greenwich. That the inclination of the plane of its Trajectory to the ecliptic is 12° 50’ 20"; the place of the descending Node ♉ 4° 12’ 50"; the place of the Perihelion ♄ 2° 58’ 0"; the distance of the Perihelion from the descending Node 88° 45’ 10"; the Logarithm of the Perihelion distance 9.528328; the Logarithm of the diurnal motion 0.667636. From these Elements (which are adapted to Dr. Halley’s general Table for the Motion of Comets in parabolic Orbits), I computed the places of this Comet for the respective times of the foregoing observations, as in the following table; which contains likewise the longitudes and latitudes deduced from the observed right ascensions and declinations, and also the differences between the computed and observed places. These differences (no-where exceeding 40") shew, that the elements here set down will be sufficient to enable future astronomers to distinguish this Comet upon another return; but as they do not correspond with the elements of the orbit of any other Comet hitherto taken notice of, we cannot determine at present the period thereof.
Greenwich, 1757.| Comet. Long.| Mean Time. | Observ. | Latit. Observ. ----------------+--------------+-----------------+ _d._ _h._ '| S. ° ’ " | ° ’ " ----------------+--------------+-----------------+ Sept. 12 16 2 | ♊ 29 34 13 | 11 32 16 No. 13 12 37 | ♋ 2 35 34 | 11 12 13 14 14 0 | 6 27 45 | 10 44 3 ----------------+-------------+-----------------+ 17 13 0 | 17 49 40 | 9 3 31 19 15 17 | 26 6 8 | 7 36 49 23 15 57 | ♌ 11 19 18 | 4 33 38 ----------------+-------------+-----------------+ 24 15 21 | 14 44 19 | 3 49 37 28 16 22 | 27 23 43 | 1 3 44 No. 30 16 24 | ♍ 2 45 43 | 0 5 30 So. ----------------+-------------+-----------------+ Octob. 2 16 48 | 7 37 43 | 1 5 50 3 16 45 | 9 51 36 | 1 32 22 4 17 0 | 12 1 4 | 1 56 42 ----------------+-------------+-----------------+ 7 16 54 | 17 51 3 | 2 56 48 8 16 53 | 19 39 45 | 3 13 7 11 16 52 | 24 47 22 | 3 48 49 17 17 12 | ♎ 4 38 58 | 4 15 42 So.
LIII. _The Resolution of a General Proposition for Determining the_ horary _Alteration of the Position of the Terrestrial Equator, from the Attraction of the Sun and Moon: With some Remarks on the Solutions given by other Authors to that difficult and important Problem. By Mr._ Tho. Simpson, _F.R.S._ [Read Dec. 22, 1757.] SINCE the time, that that excellent Astronomer, my much honoured friend Dr. Bradley, published his observations and discoveries concerning the inequalities of the precession of the equinox, and of the obliquity of the ecliptic, depending on the position of the lunar nodes, mathematicians, in different parts of Europe, have set themselves diligently to compute, from physical principles, the effects produced by the sun and moon, in the position of the terrestrial equator; and to examine whether these effects do really correspond with the observations. Two papers on this subject have already appeared in the Philosophical Transactions; in which the authors have shewn evident marks of skill and penetration. There is, nevertheless, one part of the subject, that seems to have been passed over without a due degree of attention, as well by both those gentlemen, as by Sir Isaac Newton himself. This part, which, upon account of physical difficulties, is indeed somewhat slippery and perplexing, I shall make the principal subject of this essay.
Text from Project Gutenberg, public domain in the United States.