130 Fufirument for exhibiting Jupiter and his Moons. handle will produce one day's motion of every fatellite; and a continuation of flow regular turns will produce a pleafing view of the following phenomena; viz. 1. The fhadows will move in nearly a ftraight line. 2. Some in a direct and others in a retrograde direction. 3. The moft diftant will frequently appear the nearest to Jupiter. 4. Near Jupiter they will move the quickeft, and floweft near their greatest elongation, where they become ftationary for a short time. 5. Their greateft elongations will be a little before quadrature, when weft; and after, when eaft of Jupiter. 6. Hence it will appear, that the fuperior portion of each orbit is greater than the inferior. 7. Whether to the eaft or weft of Jupiter, their motions will be direct in the fuperior, and retrograde in the inferior, parts of their orbits. 8. When paffing between Jupiter and the earth (candle) they will tranfit him. 9. When paffing the fame line in their fuperior femicircle they will fuffer an occultation. 10. When paffing through the four concentric circles they will be eclipfed. 11. The mean or apparent times, accordingly as the inftrument may be rectified, of each of these phenomena, will be pointed out by the hour-hand, the name of the day by the week-hand, and the day of the month by the month-hand, in each year. 12. If the candlestick is adjusted frequently for the fun's place and Jupiter's heliocentric Iongitude, the folar fhadow will appear to alter its fituation to the right and left of Jupiter, as he approaches to or recedes from conjunction or oppofition. 13. The reafon will be evident, from the concentric circles, why an immerfion or ingrefs into Jupiter's fhadow, and a fubfequent emerfion or egrefs out of it, never both happen with the first and second satellites; nor with the third, if Jupiter is within 46° of oppofition to, or conjunction with, the fun; nor with the fourth, if that diftance is lefs than 24°. 14. It will be likewise evident why an immersion only is vifible of the first and second fatellites from a conjunction to an oppofition (fig. 6.), why an occultation and eclipse may be coincident when at opposition (fig. 5.), and why an emerfion only is seen from an oppofition to a conjunction (fig. 4.). 15. If a proper reclination be given to the fatellitian in this and on the next year, and alfo on every fixth and seventh year hence, the fourth fatellite will neither be eclipfed nor fuffer an occultation. 16. If a candle be now placed in each focket of different lengths, as is reprefented in fig. 3. the fhadow of the central one to cover the concentric circles, there will be two rows of fhadows on the fcreen above one another, one of which will reprefent the heliocentric, and the other the geocentric, places of the fatellites. An immersion and fubfequent emerfion may be seen of the fecond fatellite, provided it be near one of its limits at the fame time that Jupiter is near both his perihelion and quadrature with the fun; but this will very rarely happen.-W. P. 17. Hence 17. Hence it will appear, that an eclipfe feen from the earth is an occultation feen from the fun. 18. That an eclipfe is never vifible at the fun. 19. And that the shadow of a fatellite, as feen from the earth, falls on Jupiter sometimes before, fometimes after, and fometimes at its tranfit, according to the relative fituations of Jupiter, the fun, and earth. 20. If the central candle only be suffered to remain, and the little balls themselves be viewed in an oblique direction, the reafon will be apparent why the fatellites are feen lunated from Jupiter: 21. And also Jupiter lunated when seen from them; 22. But neither of them lunated when feen from the earth or fun. 23. It will also be evident why the fun is frequently eclipfed to the inhabitants of Jupiter by the fhadows of his fatellites. 24. And, lastly, why the fatellites, as feen from the earth, do not eclipfe one another. These, and perhaps other phenomena not specified here, will be illuftrated by the fatellitian in fo diftinct a manner, as to convey to a fpectator, who may compare the apparent motions of the fhadows to the real motions of the little balls, a clear conception of the relation that the apparent motions of Jupiter's fatellites, as viewed from the earth with a telescope, have to their true circular motions, as viewed by the inhabitants of Jupiter. But though a clear conception may thus be formed by a spectator of the true and apparent motions of the fatellites as they regard Jupiter himself, yet he must be informed that the real track in which they move round the fun along with Jupiter, the progreffive centre of their detached system, is neither circular nor elliptical, but in a line which croffes Jupiter's track in a finuofe manner, more or lefs frequently as their periods are fhorter or longer. As the velocity of the first and second fatellites exceeds the velocity of Jupiter, they are not only apparently, but really retrograde in fome part of every revolution; on which account their tracks form loops which are alternately concave and convex towards the fun; the concavity being greater than the convexity: but as the velocity of Jupiter exceeds that of the third and fourth, these are not really but only apparently retrograde at the inferior femicircles on this account their tracks are always concave, except at their stationary points, which project and divide the concave spaces. These real tracks will easily be comprehended, if, while the fatellites are in motion, Jupiter himself be alfo conceived to have a direct motion flower than the two first, but quicker than the two last. : If now, after what has been said, we conceive ourselves, like the philosophical poet *, conveyed into the regions of Jupiter and his fatellites, we fhall with him find caufe for adoring the power, wisdom, and goodness of the Almighty Creator! When we confider that Jupiter, the diameter of which planet is more than ten times larger than that of our earth, has a rotation on its axis in the small space of nine hours and fifty-fix minutes, we "remote from day's all-cheering fource, BAKER'S Univerfe. muft 132 Jupiter's Moons.-Luminous Infects. must perceive, that, without the affiftance of fome other luminary befides the fun, total darkness would be the lot of his inhabitants for nearly five hours in every ten.-Again, if we confider that Jupiter's year, or periodical revolution, contains 4332 d. 8 h. 51 min. of our time, or 22936,43+ of his own days, and that he has no fenfible change of feasons, by reason of the nearly perpendicular direction of his axis, the inclination of which is only 1° 20′, we must see that the number of his days in his year might frequently be loft, without fome intermediate remembrancers between those two very distant extremes: accordingly, the Omnipotent Father of the creation has provided a remedy for these inconveniences he has furnished Jupiter with thefe four moons to cheer his inhabitants with light in the frequent abfence of the fun's rays, and to prefent them with four different kinds of months, like our years, months, and weeks. Of the first kind of months in Jupiter's year there are 244,97+, each of which contains 9,36+ of his days; of the second kind there are 121,89+, each containing 18,81+; of the third kind there are 60,45+, each comprising 37,94 +; and of the fourth kind there are only 25,85+, each of which comprises 88,68 + of his days; so that each shorter month, particularly of the three first kinds, is very nearly double the next longer; and may be confidered as exactly fuch, in counting time by divisions and subdivisions of months, by the help of intercalary days. But befides these uses of Jupiter's fatellites, and others, perhaps, which our limited capacities can never comprehend, there are three very confiderable advantages, which the inhabitants of our globe poffefs, accruing from the observations which have already been made upon them; viz. an accurate knowledge of the parallax of the earth's annual orbit; of the real velocity of light; and of an easy method of ascertaining the longitude of places by land; all which are explained in the different books upon aftronomy :-so true is it throughout the whole grand scale of nature, that no individual part is without its utility. Lincoln, March 10, 1798. VI. Objections to the Opinion of Professor Spallanzani respecting the Caufe of the Light of Natural Phofphori. Communicated to Mr. John Fabbroni, Sub-Director of the Royal Museum of Florence. By M. JOACHIM CARRADORI, M. D:* AT length the hypothefis of Goettling is entirely destroyed, in confequence of the refutations of various celebrated authors, and among them Spallanzani. You may perhaps recollect that. I foretold its fhort duration, and I pointed out to Brugnatelli, at its first appearance, several proofs of its falfity, which might be deduced from the very experiments it was built upon. Though the refutation of Spallanzani †has not the merit of being the firft, its excellence * Annales de Chimie, xxiv. 216. + Chimico Efame del Cittadino Spallanzani. Modena. 1796. cannot On the Light of Natural Phosphori. 133 cannot be difputed. I have read this short treatise with pleasure, from the many excellent and amusing points of knowledge it contains. But on perufing it with a certain degree of attention, I cannot avoid making feveral obfervations which the facts appear to demand. It appears to me that Spallanzani fuppofes himself to be the first who obferved that water has the property of absorbing oxygen from the air of the atmosphere. For at the. 114th page of his book, he fays: Trovai pertanto che l'acqua e' un mezzo di decomporre l'arie, come lo fono il fosforo di Kunckel e i fulfuri alcalini; mà ella agisce con eftrema lentezza. "I found, however, that water is a medium for decompofing the air in the fame manner as Kunckel's phosphorus, or the alcaline fulphurets; but it acts with extreme flowness."-But this fact was already known to Scheele (Treatise of Air and Fire), and confequently the honour of this difcovery is his right. He was the first who obferved that, by keeping a bottle of atmospheric air inverted over water for feveral days, the water gradually rifes; the volume of air is diminished, and azotic gas, or, as it was then called, phlogisticated air, remains alone. It is surprising that Spallanzani should not be aware of this; or, if he knew it, that he should have omitted mentioning it. I have very important facts to state against his theory of natural phosphori. It is long fince I first observed that the phofphoric wood not only fhines under water and under oil, but even in the barometric vacuum; which obfervations are related in the fecond volume of my theory of heat. If the phofphoric wood require air to enable it to fhine, how can it continue to emit light under oil, where the vital air neither exifts nor can have accefs? I must likewise remark the difference which Spallanzani has observed between the urinous phosphorus and that of wood; namely, that when the former is entirely furrounded by any pure mephitic air, it immediately ceafes to give light; whereas the other being placed it pure azotic air continues to fhine during fix minutes, and does not entirely lofe its light till half an hour afterwards. When Spallanzani introduced phosphoric wood into vital air, or oxygen gas, how did it happen that he omitted to observe, whether by its fhining in that fluid for a confiderable. time, there was no diminution of volume, as he observed that this diminution took place when the phosphoric flies (lucciole) were placed therein ? The luccioloni, or glow-worms, as well as the lucciole, fhine under oil. I have obferved a luminous fly continue to fhine perfectly for a quarter of an hour in the barometric vacuum. Spallanzani found that the phosphorus of these flies shines much more in oxygen gas than in the air of the atmosphere, and is totally extinguished by air not capable of maintaining combustion. But how can we explain their shining under oil for hours together?: The fact is certain, because I have repeated the experiment with many variations; fome-. times by putting the phosphoric flies entire beneath the oil, and fometimes the phosphorus only detached from the infect, and even crushed. This obfervation must be well known to you, fince I communicated it last year to the Royal and Oeconomical Society of Florence, in my Memoir on the Lucciole; and it will be equally known to the whole scientific world, as it will be published in the xiiith volume. of the Chemical Annals of the celebrated Brugnatelli. The 134 On the Light of Natural Phosphori. The experiment of placing the luminous flies in oxygen is not new. It was before made by Forster; for which fee his Theory of Heat, and the Journal de Rozier for 1784. He observed that they give much more heat in this fluid, not only at intervals, but continually. M. Forfter moreover affures us, that he discovered the organs of respiration in those infects, which M. Spallanzani could not find. He defcribes them precifely, by obferving that in each of the luminous rings there are two air paffages, furnished with valvules at their apertures, and that these paffages are loft in the interior structure of the animal. I have seen two species of luccioloni, or shining worms; namely, a larger and a smaller, of which I have given a flight description in my Theory of Heat, where I speak of phosphori. The firft fpecies alfo differs from the fecond in colour; the former being nearly grey, and the latter nearly black. The firft have much luminous matter in the three laft rings; and the others have lefs in the last ring but one. These may perhaps have been the fpecies obferved by the Naturalift of Pavia. Both species conceal their phosphorus at pleasure with the utmost facility. They feem therefore to be aware of its effects, particularly the second species. It is not true, as certain naturalifts, as well as M. Spallanzani, pretend, that the luccioloni and lucciole are animals of the fame fpecies, different only in fex, that is to fay, that the former are the males, and the latter the females. I can affirm that I have feen the lucciole pregnant, with the abdomen filled with eggs: and this part, which before was fo luminous, had its phosphoric part very much diminished, being reduced to merely two points, and two small lateral portions. The lucciole begin to disappear precisely at the time of their pregnancy, which is the cause why they conceal themselves. If they be fought for among the grass and underwood, they are found in this state*. If it be certain then that phosphoric wood, the luccioloni and the lucciole continues shine under oil, it must be admitted that this light does not arife from a flow combustion, as Spallanzani pretends, because oil contains no air to fupport it. This is the legitimate and immediate confequence which must follow from this experiment, and cannot be refused. The experiments of Spallanzani lead to peculiar consequences, though different from those he has deduced. It is poffible that the unrefpirable air may act in a particular manner on these phosphori, which may be capable of preventing the emanation of their lights; and that oxygen, by a particular action of a contrary kind, may augment it. Why should it be disputed that the different airs may produce peculiar effects on these substances, with which we are not yet acquainted? To Spallanzani will be due the honour of first observing them. In the fame manner as various fluids are pernicious to natural phosphori, and prevent their shining, why may not the air produce the fame effect? I have found by experiment, that the phosphorus of the lucciole is fuddenly extinguished if they be plunged in alcohol, or in vinegar; but continues to fhine in oil in the fame manner as in water and in air. It may be objected to me, that Spallanzani has made the experiment, that the phosphorus of the shining worms produces a diminution of volume in oxygen gas, at the fame time that their light is increased; whence it ought to be concluded that the process is analogous * See the note No. 1. p. 78. tom. ii. of my Theory of Heat. C. to |