Chaps. 9-14.

Chap. 9. (12.)—An Account of the Observations That Have Been Made on the Heavens by Different Individuals.

The first among the Romans, who explained to the people at large the cause of the two kinds of eclipses, was Sulpicius Gallus, who was consul along with Marcellus; and when he was only a military tribune he relieved the army from great anxiety the day before king Perseus was conquered by Paulus [This eclipse is calculated to have occurred on the 28th of June, 168 B.C.; Brewster’s Encyc. “Chronology,” p. 415, 424. We have an account of this transaction in Livy, xliv. 37, and in Plutarch, Life of Paulus Æmilius, Langhorne’s trans. ii. 279; he however does not mention the name of Gallus. See also Val. Maximus, viii. 11. 1, and Quintilian, i. 10. Val. Maximus does not say that Gallus predicted the eclipse, but explained the cause of it when it had occurred; and the same statement is made by Cicero, De Repub. i. 15. For an account of Sulpicius, see Hardouin’s Index auctorum, Lemaire, i. 214.]; for he was brought by the general into a public assembly, in order to predict the eclipse, of which he afterwards gave an account in a separate treatise. Among the Greeks, Thales the Milesian first investigated the subject, in the fourth year of the forty-eighth olympiad, predicting the eclipse of the sun which took place in the reign of Alyattes, in the 170th year of the City [An account of this event is given by Herodotus, Clio, § 74. There has been the same kind of discussion among the commentators, respecting the dates in the text, as was noticed above, note, p. 29: see the remarks of Brotier and of Marcus in Lemaire and Ajasson, in loco. Astronomers have calculated that the eclipse took place May 28th, 585 B.C.; Brewster, ut supra, pp. 414, 419.]. After them Hipparchus calculated the course of both these stars for the term of 600 years [Hipparchus is generally regarded as the first astronomer who prosecuted the science in a regular and systematic manner. See Whewell, C. 3. p. 169 et seq., 177-179. He is supposed to have made his observations between the years 160 and 125 B.C. He made a catalogue of the fixed stars, which is preserved in Ptolemy’s Magn. Const. The only work of his now extant is his commentary on Aratus; it is contained in Petau’s Uranologie. We find, among the ancients, many traces of their acquaintance with the period of 600 years, or what is termed the great year, when the solar and lunar phænomena recur precisely at the same points. Cassini, Mem. Acad., and Bailly, Hist. Anc. Astron., have shown that there is an actual foundation for this opinion. See the remarks of Marcus in Ajasson, ii. 302, 303.], including the months, days, and hours, the situation of the different places and the aspects adapted to each of them; all this has been confirmed by experience, and could only be acquired by partaking, as it were, in the councils of nature. These were indeed great men, superior to ordinary mortals, who having discovered the laws of these divine bodies, relieved the miserable mind of man from the fear which he had of eclipses, as foretelling some dreadful events or the destruction of the stars. This alarm is freely acknowledged in the sublime strains of Stesichorus and Pindar, as being produced by an eclipse of the sun [Seneca, the tragedian, refers to this superstitious opinion in some beautiful verses, which are given to the chorus at the termination of the fourth act of the Thyestes.]. And with respect to the eclipse of the moon, mortals impute it to witchcraft, and therefore endeavour to aid her by producing discordant sounds. In consequence of this kind of terror it was that Nicias, the general of the Athenians, being ignorant of the cause, was afraid to lead out the fleet, and brought great distress on his troops [We have an account of this event in Thucydides, Smith’s trans. ii. 244, and in Plutarch, Langhorne’s trans. iii. 406. It is calculated to have happened Aug. 27th, 413 B.C.; Brewster, ut supra, p. 415, 421.]. Hail to your genius, ye interpreters of heaven! ye who comprehend the nature of things, and who have discovered a mode of reasoning by which ye have conquered both gods and men [The elegant lines of Ovid, in his Fasti, i. 297 et seq., express the same sentiment: “Felices animos, quibus hoc cognoscere primis,” &c.]! For who is there, in observing these things and seeing the labours [I have already remarked upon the use of this term as applied to the eclipses of the moon in note, p. 31.] which the stars are compelled to undergo (since we have chosen to apply this term to them), that would not cheerfully submit to his fate, as one born to die? I shall now, in a brief and summary manner, touch on those points in which we are agreed, giving the reasons where it is necessary to do so; for this is not a work of profound argument, nor is it less wonderful to be able to suggest a probable cause for everything, than to give a complete account of a few of them only.

Chap. 10. (13.)—On the Recurrence of the Eclipses of the Sun and the Moon.

It is ascertained that the eclipses complete their whole revolution in the space of 223 months [According to the remarks of Marcus, it appears probable that this sol-lunar period, as it has been termed, was discovered by the Chaldeans; Ajasson, ii. 306, 307.], that the eclipse of the sun takes place only at the conclusion or the commencement of a lunation, which is termed conjunction [“coitus.”], while an eclipse of the moon takes place only when she is at the full, and is always a little farther advanced than the preceding eclipse [“Hoc enim periodo (223 mensium) plerumque redeunt eclipses, non multum differentes, denis tamen gradibus zodiaci antecedentes;” Kepler, as quoted by Alexandre, in Lemaire, ii. 238.]. Now there are eclipses of both these stars in every year, which take place below the earth, at stated days and hours; and when they are above it [The terms “sub terra” and “superne” are interpreted, by most of the commentators, below and above the horizon respectively; see Marcus in Ajasson, ii. 307.] they are not always visible, sometimes on account of the clouds, but more frequently, from the globe of the earth being opposed to the vault of the heavens [“globo terræ obstante convexitatibus mundi.” The term convexus, as applied to the heavens, or visible firmament, simply signifies arched; not opposed to concave, like the English word convex.]. It was discovered two hundred years ago, by the sagacity of Hipparchus, that the moon is sometimes eclipsed after an interval of five months, and the sun after an interval of seven [This point is discussed by Ptolemy, Magn. Const. vi. 6; “De distantia eclipticorum mensium.” See also the remarks of Hardouin in Lemaire, ii. 260, 261; and of Poinsinet, i. 67.]; also, that he becomes invisible, while above the horizon, twice in every thirty days, but that this is seen in different places at different times. But the most wonderful circumstance is, that while it is admitted that the moon is darkened by the shadow of the earth, this occurs at one time on its western, and at another time on its eastern side. And farther, that although, after the rising of the sun, that darkening shadow ought to be below the earth, yet it has once happened, that the moon has been eclipsed in the west, while both the luminaries have been above the horizon [These are styled horizontal eclipses; they depend on the refractive power of the atmosphere, causing the sun to be visible above the horizon, although it is actually below it. Brotier states, that eclipses of this description occurred on the 17th July, 1590, on the 30th November, 1648, and on the 16th January, 1660; Lemaire, ii. 260.]. And as to their both being invisible in the space of fifteen days, this very thing happened while the Vespasians were emperors, the father being consul for the third time, and the son for the second [This is supposed to have been in the year 72 of our æra, when it is said that the sun was eclipsed, in Italy, on the 8th, and the moon on the 22nd of February; see Hardouin and Alexandre, in Lemaire, ii. 261.].

Chap. 11. (14.)—Of the Motion of the Moon.

It is certain that the moon, having her horns always turned from the sun, when she is waxing, looks towards the east; when she is waning, towards the west. Also, that, from the second day after the change, she adds 47 1 / 2 minutes [In a subsequent part of the work, xviii. 75, the author gives a different rate of increase, viz. 51 1 / 2 minutes; neither of these numbers is correct; the mean rate of increase being, according to Alexandre, about 54′ or 55′; Lemaire, ii. 261, 262. See also Marcus in Ajasson, ii. 311-14.] each day, until she is full, and again decreases at the same rate, and that she always becomes invisible when she is within 14 degrees of the sun. This is an argument of the greater size of the planets than of the moon, since these emerge when they are at the distance of 7 degrees only [It is scarcely necessary to remark, that the effect, as here stated, has no connexion with the supposed cause.]. But their altitude causes them to appear much smaller, as we observe that, during the day, the brightness of the sun prevents those bodies from being seen which are fixed in the firmament, although they shine then as well as in the night: that this is the case is proved by eclipses, and by descending into very deep wells.

Chap. 12. (15.)—Of the Motions of the Planets and the General Laws of Their Aspects.

The three planets, which, as we have said, are situated above the sun [Mars, Jupiter, and Saturn.], are visible when they come into conjunction with him. They rise visibly [They are then said, in astronomical language, to rise heliacally.] in the morning, when they are not more than 11 degrees from the sun [In the last chapter this distance was stated to be 7 degrees; see the remarks of Alexandre, in Lemaire, ii. 263.]; they are afterwards directed by the contact of his rays [“radiorum ejus contactu reguntur.” The doctrine of the ancient astronomers was, that the motions of the planets are always governed by the rays of the sun, according to its position, attracting or repelling them.], and when they attain the trine aspect, at the distance of 120 degrees, they take their morning stationary positions [A planet appears to be stationary, i. e. to be referred to the same point of the zodiac, when it is so situated with respect to the earth, that a straight line passing through the two bodies forms a tangent to the smaller orbit. The apparent motion of the planets, sometimes direct and at other times retrograde, with their stationary positions, is occasioned by the earth and the planets moving in concentric orbits, with different velocities. One hundred and twenty degrees is the mean distance at which the three superior planets become stationary. We have an elaborate dissertation by Marcus, on the unequal velocities of the planets, and on their stations and retrogradations, as well according to the system of Aristotle as to that of Copernicus; Ajasson, ii. 316 et seq. He remarks, and, I conceive, with justice, “... ce n’est pas dans les traités d’astronomie de nos savans que l’on doit puiser les détails destinés à éclaircir le texte des chapitres xii, xiii, xiv et xv du second livre de Pline.... Je ne dis rien des commentaires de Poinsinet, d’Hardouin et d’autres savans peu versés en matière d’astronomie, qui ont fait dire à Pline les plus grandes absurdités. ”], which are termed primary; afterwards, when they are in opposition to the sun, they rise at the distance of 180 degrees from him. And again advancing on the other side to the 120th degree, they attain their evening stations, which are termed secondary, until the sun having arrived within 12 degrees of them, what is called their evening setting becomes no longer visible [“Occasus planetæ vespertinus dicitur, quo die desinit post occasum solis supra horizontem oculis se præbere manifestum;” Alexandre in Lemaire, ii. 265. It is then said to set heliacally.]. Mars, as being nearer to the sun, feels the influence of his rays in the quadrature, at the distance of 90 degrees, whence that motion receives its name, being termed, from the two risings, respectively the first and the second nonagenarian [The interpretation of this passage has given rise to much discussion among the commentators and translators; I may refer the reader to the remarks of Poinsinet, i. 70, 71; of Alexandre in Lemaire, ii. 266; and of Marcus in Ajasson, ii. 328. I conceive the meaning of the author to be, that while the other planets become stationary, when at 120 degrees from the sun, Mars becomes so at 90 degrees, being detained by the rays, which act upon him more powerfully, in consequence of his being nearer to their source.]. This planet passes from one station to another in six months, or is two months in each sign; the two other planets do not spend more than four months in passing from station to station.

The two inferior planets are, in like manner, concealed in their evening conjunction, and, when they have left the sun, they rise in the morning the same number of degrees distant from him. After having arrived at their point of greatest elongation [I may refer to the remarks of Marcus on the respective distances from the sun at which Venus and Mercury become stationary, and when they attain their greatest elongations; Ajasson, ii. 328, 329. According to Ptolemy, Magn. Constr. lib. viii. cap. 7, the evening setting of Venus is at 5° 40′ from the sun, and that of Mercury at 11° 30′.], they then follow the sun, and having overtaken him at their morning setting, they become invisible and pass beyond him. They then rise in the evening, at the distances which were mentioned above. After this they return back to the sun and are concealed in their evening setting. The star Venus becomes stationary when at its two points of greatest elongation, that of the morning and of the evening, according to their respective risings. The stationary points of Mercury are so very brief, that they cannot be correctly observed.

Chap. 13.—Why the Same Stars Appear at Some Times More Lofty and at Other Times More Near.

The above is an account of the aspects and the occultations of the planets, a subject which is rendered very complicated by their motions, and is involved in much that is wonderful; especially, when we observe that they change their size and colour, and that the same stars at one time approach the north, and then go to the south, and are now seen near the earth, and then suddenly approach the heavens. If on this subject I deliver opinions different from my predecessors, I acknowledge that I am indebted for them to those individuals who first pointed out to us the proper mode of inquiry; let no one then ever despair of benefiting future ages.

But these things depend upon many different causes. The first cause is the nature of the circles described by the stars, which the Greeks term apsides [“ Ἁψὶς, ligneus rotæ circulus, ab ἅπτω necto;” Hederic in loco. The term is employed in a somewhat different sense by the modern astronomers, to signify the point in the orbit of a planet, when it is either at the greatest or the least distance from the earth, or the body about which it revolves; the former being termed the apogee, aphelion, or the higher apsis; the latter the perigee, perhelion, or lower apsis; Jennings on the Globes, pp. 64, 65.], for we are obliged to use Greek terms. Now each of the planets has its own circle, and this a different one from that of the world [“mundo.”]; because the earth is placed in the centre of the heavens, with respect to the two extremities, which are called the poles, and also in that of the zodiac, which is situated obliquely between them. And all these things are made evident by the infallible results which we obtain by the use of the compasses [“ratione circini semper indubitata.”]. Hence the apsides of the planets have each of them different centres, and consequently they have different orbits and motions, since it necessarily follows, that the interior apsides are the shortest.

(16.) The apsides which are the highest from the centre of the earth are, for Saturn, when he is in Scorpio, for Jupiter in Virgo, for Mars in Leo, for the Sun in Gemini, for Venus in Sagittarius, and for Mercury in Capricorn, each of them in the middle of these signs; while in the opposite signs, they are the lowest and nearest to the centre of the earth [In consequence of the precession of the equinoxes these points are continually advancing from W. to E., and are now about 30 degrees from the situation they were in when the observations were first made by the modern astronomers.]. Hence it is that they appear to move more slowly when they are carried along the highest circuit; not that their actual motions are accelerated or retarded, these being fixed and determinate for each of them; but because it necessarily follows, that lines drawn from the highest apsis must approach nearer to each other at the centre, like the spokes of a wheel; and that the same motion seems to be at one time greater, and at another time less, according to the distance from the centre.

Another cause of the altitudes of the planets is, that their highest apsides, with relation to their own centres, are in different signs from those mentioned above [Our author here probably refers to the motions of the planets through their epicycles or secondary circles, the centres of which were supposed to be in the peripheries of the primary circles. See Alexandre in Lemaire, ii. 270.]. Saturn is in the 20th degree of Libra, Jupiter in the 15th of Cancer, Mars in the 28th of Capricorn, the Sun in the 19th of Aries, Venus in the 27th of Pisces, Mercury in the 15th of Virgo, and the Moon in the 3rd of Taurus.

The third cause of the altitude depends on the form of the heavens, not on that of the orbits; the stars appearing to the eye to mount up and to descend through the depth of the air [It is to this visible appearance of convexity in the heavens that Ovid refers in the story of Phaëton, where he is describing the daily path of the sun; Metam. ii. 63-67.]. With this cause is connected that which depends on the latitude of the planets and the obliquity of the zodiac. It is through this belt that the stars which I have spoken of are carried, nor is there any part of the world habitable, except what lies under it [“quam quod illi subjacet;” under this designation the author obviously meant to include the temperate zones, although it technically applies only to the part between the tropics. It is scarcely necessary to remark, that modern discoveries have shown that this opinion respecting the Arctic zone is not strictly correct.]; the remainder, which is at the poles, being in a wild desert state. The planet Venus alone exceeds it by 2 degrees, which we may suppose to be the cause why some animals are produced even in these desert regions of the earth. The moon also wanders the whole breadth of the zodiac, but never exceeds it. Next to these the planet Mercury moves through the greatest space; yet out of the 12 degrees (for there are so many degrees of latitude in the zodiac [The breadth of the zodiac, which was limited by the ancients to 12 degrees, has been extended by the modern astronomers to 18, and would require to be much farther extended to include the newly discovered planet. Herschel’s Astronomy, § 254.]), it does not pass through more than 8, nor does it go equally through these, 2 of them being in the middle of the zodiac, 4 in the upper part, and 2 in the lower part [There is considerable difficulty in ascertaining the meaning of the terms employed by our author in describing the course of the planet Mercury through the zodiac; “medio ejus,” “supra,” and “infra.” Hardouin’s comment is as follows: “Duas zodiaci partes seu gradus pererrat, quum ipse per medium incedit signiferum: supra, quum deflectit ad Aquilonem, per quatuor alias ejusdem partes vagatur: infra, quum descendit ad Austrum, discedit duabus.” Lemaire, ii. 271, 272. But Marcus has shown that the opinion of Hardouin is inadmissible and inconsistent with the facts; Ajasson, ii. 338-341. He proposes one, which he conceives to be more correct, but we may probably be led to the conclusion, that the imperfect knowledge and incorrect opinions of our author on these subjects must render it impossible to afford an adequate explanation.]. Next to these the Sun is carried through the middle of the zodiac, winding unequally through the two parts of his tortuous circuit [“flexuoso draconum meatu;” Poinsinet remarks, “Les Grecs... appellaient dragons les bracelets, les hausse-cols, les chainettes, et généralement tout ce qui avait une figure armillaire;” i. 79, 80.]. The star Mars occupies the four middle degrees; Jupiter the middle degree and the two above it; Saturn, like the sun, occupies two [As this remark appears to contradict what was said in the last sentence respecting the sun, we may suspect some error in the text; see Poinsinet, Alexandre, and Marcus, in loco.]. The above is an account of the latitudes as they descend to the south or ascend to the north [The following comparative statement is given by Alexandre of the geocentric latitudes of the planets, as assigned by Pliny, and as laid down by the moderns. Lemaire, ii. 273:— Pliny. Moderns. Venus 8° 9° 22′ Moon 6 6 0 Mercury 5 6 54 Mars 2 0 1 51 Jupiter 1 30 1 30 Saturn 1 (or 2°) 2 30]. Hence it is plain that the generality of persons are mistaken in supposing the third cause of the apparent altitude to depend on the stars rising from the earth and climbing up the heavens. But to refute this opinion it is necessary to consider the subject with very great minuteness, and to embrace all the causes.

It is generally admitted, that the stars [It appears from the remark at the end of this chapter, that this explanation applies to the superior planets alone.], at the time of their evening setting, are nearest to the earth, both with respect to latitude and altitude [It is not easy, as Marcus observes, Ajasson, ii. 341, 345, to comprehend the exact meaning of this passage, or to reconcile it with the other parts of our author’s theory.], that they are at the commencement of both at their morning risings, and that they become stationary at the middle points of their latitudes, what are called the ecliptics [“Ecliptica,” called by the moderns the nodes; i. e. the two points where the orbits of the planets cut the ecliptic. See the remarks of Marcus on this term; Ajasson, ii. 345, 346.]. It is, moreover, acknowledged, that their motion is increased when they are in the vicinity of the earth, and diminished when they are removed to a greater altitude [We may presume that our author here refers to the apparent motion of the planets, not to their actual acceleration or retardation.]; a point which is most clearly proved by the different altitudes of the moon. There is no doubt that it is also increased at the morning risings [The editors have differed in the reading of this passage; I have followed that of Lemaire.], and that the three superior planets are retarded, as they advance from the first station to the second. And since this is the case, it is evident, that the latitudes are increased from the time of their morning risings, since the motions afterwards appear to receive less addition; but they gain their altitude in the first station, since the rate of their motion then begins to diminish [“incipit detrahi numerus.” According to the explanation of Alexandre, “numerus nempe partium quas certo temporis intervallo emetiuntur.” Lemaire, ii. 275. Marcus remarks in this place, “ Dans tout ce chapitre et dans le suivant, Pline a placé dans une correlation de causité, tout ce qu’il croit arriver en même temps; mais il n’a pas prouvé par-là que les phenomènes célestes qui sont contemporains sont engendrés les uns par les autres. ” Ajasson, ii. 349.], and the stars to recede.

And the reason of this must be particularly set forth. When the planets are struck by the rays of the sun, in the situation which I have described, i. e. in their quadrature, they are prevented from holding on their straight forward course, and are raised on high by the force of the fire [The hypothesis of Pliny appears to be, that the planets are affected by the rays of the sun, and that according to the angle at which they receive the impulse, they are either accelerated or retarded in their course.]. This cannot be immediately perceived by the eye, and therefore they seem to be stationary, and hence the term station is derived. Afterwards the violence of the rays increases, and the vapour being beaten back forces them to recede.

This exists in a greater degree in their evening risings, the sun being then turned entirely from them, when they are drawn into the highest apsides; and they are then the least visible, since they are at their greatest altitude and are carried along with the least motion, as much less indeed as this takes place in the highest signs of the apsides. At the time of the evening rising the latitude decreases and becomes less as the motion is diminished, and it does not increase again until they arrive at the second station, when the altitude is also diminished; the sun’s rays then coming from the other side, the same force now therefore propels them towards the earth which before raised them into the heavens, from their former triangular aspect [“ex priore triquetro.”]. So different is the effect whether the rays strike the planets from below or come to them from above. And all these circumstances produce much more effect when they occur in the evening setting. This is the doctrine of the superior planets; that of the others is more difficult, and has never been laid down by any one before me [Alexandre supposes, as I conceive justly, that our author, in this passage, only refers to the writings of his own countrymen; Lemaire, ii. 276.].

Chap. 14. (17.)—Why the Same Stars Have Different Motions.

I must first state the cause, why the star Venus never recedes from the sun more than 46 degrees, nor Mercury more than 23 [According to Ptolemy, these numbers are respectively 47° 51′ and 24° 3′; the modern astronomers have ascertained them to be 48° and 29°. The least elongations of the planets are, according to Ptolemy, 44° 7′ and 18° 50′, and according to the observations of the moderns, 45° and 16°; Marcus in Ajasson, ii. 354.], while they frequently return to the sun within this distance [I have not translated the clause, “quum sint diversæ stelæ,” as, according to Hardouin, it is not found “in probatissimis codd.,” and appears to have little connexion with the other parts of the sentence; it is omitted by Valpy and Lemaire, but is retained by Poinsinet and Ajasson.]. As they are situated below the sun, they have both of them their apsides turned in the contrary direction; their orbits are as much below the earth as those of the stars above mentioned are above it, and therefore they cannot recede any farther, since the curve of their apsides has no greater longitude [When these inferior planets have arrived at a certain apparent distance from the sun, they are come to the extent of their orbits, as seen from the earth.]. The extreme parts of their apsides therefore assign the limits to each of them in the same manner, and compensate, as it were, for the small extent of their longitudes, by the great divergence of their latitudes [“Quum ad illam Solis distantiam pervenerunt, ultra procedere non possunt, deficiente circuli longitudine, id est, amplitudine.” Alexandre in Lemaire, ii. 277.]. It may be asked, why do they not always proceed as far as the 46th and the 23rd degrees respectively? They in reality do so, but the theory fails us here. For it would appear that the apsides are themselves moved, as they never pass over the sun [The transits of the inferior planets had not been observed by the ancients.]. When therefore they have arrived at the extremities of their orbits on either side, the stars are then supposed to have proceeded to their greatest distance; when they have been a certain number of degrees within their orbits, they are then supposed to return more rapidly, since the extreme point in each is the same. And on this account it is that the direction of their motion appears to be changed. For the superior planets are carried along the most quickly in their evening setting, while these move the most slowly; the former are at their greatest distance from the earth when they move the most slowly, the latter when they move the most quickly. The former are accelerated when nearest to the earth, the latter when at the extremity of the circle; in the former the rapidity of the motion begins to diminish at their morning risings, in the latter it begins to increase; the former are retrograde from their morning to their evening station, while Venus is retrograde from the evening to the morning station. She begins to increase her latitude from her morning rising, her altitude follows the sun from her morning station, her motion being the quickest and her altitude the greatest in her morning setting. Her latitude decreases and her altitude diminishes from her evening rising, she becomes retrograde, and at the same time decreases in her altitude from her evening station.

Again, the star Mercury, in the same way, mounts up in both directions [“utroque modo;” “latitudine et altitudine;” Hardouin in Lemaire, ii. 279.] from his morning rising, and having followed the sun through a space of 15 degrees, he becomes almost stationary for four days. Presently he diminishes his altitude, and recedes from his evening setting to his morning rising. Mercury and the Moon are the only planets which descend for the same number of days that they ascend. Venus ascends for fifteen days and somewhat more; Saturn and Jupiter descend in twice that number of days, and Mars in four times. So great is the variety of nature! The reason of it is, however, evident; for those planets which are forced up by the vapour of the sun likewise descend with difficulty.