III
THALES
SUCH astronomy as we find in Homer and Hesiod was of the merely practical kind, which uses the celestial recurrences for the regulation of daily life; but, as the author of the Epinomis says, ‘the true astronomer will not be the man who cultivates astronomy in the manner of Hesiod and any other writers of that type, concerning himself only with such things as settings and risings, but the man who will investigate the seven revolutions included in the eight revolutions and each describing the same circular orbit [i. e. the separate motions of the sun, moon, and the five planets combined with the eighth motion, that of the sphere of the fixed stars, or the daily rotation], which speculations can never be easily mastered by the ordinary person but demand extraordinary powers’. The history of Greek astronomy in the sense of astronomy proper, the astronomy which seeks to explain the heavenly phenomena and their causes, begins with Thales.
Thales of Miletus lived probably from about 624 to 547 B.C. (though according to Apollodorus he was born in 640/39). According to Herodotus, his ancestry was Phoenician; his mother was Greek, to judge by her name Cleobuline, while his father’s name, Examyes, is Carian, so that he was of mixed descent. In 582/1 B.C. he was declared one of the Seven Wise Men, and indeed his versatility was extraordinary; statesman, engineer, mathematician and astronomer, he was an acute business man in addition, if we may believe the story that, wishing to show that it was easy to get rich, he took the opportunity of a year in which he foresaw that there would be a great crop of olives to get control of all the oil-presses in Miletus and Chios in advance, paying a low rental when there was no one to bid against him, and then, when the accommodation was urgently wanted, charging as much as he liked for it, with the result that he made a large profit.1 For his many-sided culture he was indebted in great measure to what he learnt on long journeys which he took, to Egypt in particular; it was in Egypt that he saw in operation the elementary methods of solving problems in practical geometry which inspired him with the idea of making geometry a deductive science depending on general propositions; and he doubtless assimilated much of the astronomical knowledge which had been accumulated there as the result of observations recorded through long centuries.
Thales’ claim to a place in the history of scientific astronomy depends almost entirely on one achievement attributed to him, that of predicting an eclipse of the sun. There is no trustworthy evidence of any other discoveries, or even of any observations, made by him, although one would like to believe the story, quoted by Plato,2 that, when he was star-gazing and fell into a well in consequence, he was rallied ‘by a clever and pretty maid-servant from Thrace’3 for being so ‘eager to know what goes on in the heavens when he could not see what was in front of him, nay, at his very feet’.
But did Thales predict a solar eclipse? The story is entirely rejected by Martin.4 He points out that, while the references to the prediction do not exactly agree, it is in fact necessary, if the occurrence of a solar eclipse at any specified place on the earth’s surface is to be predicted with any prospect of success, to know more of the elements of astronomy than Thales could have known, and in particular to allow for parallax, which was not done until much later, and then only approximately, by Hipparchus. Further, if the prophecy had rested on any scientific basis, it is incredible that the basis should not have been known and been used by later Ionian philosophers for making other similar predictions, whereas we hear of none such in Greece for two hundred years. Indeed, only one other supposed prediction of the same kind is referred to. Plutarch5 relates that, when Plato was on a visit to Sicily and staying with Dionysius, Helicon of Cyzicus, a friend of Plato’s, foretold a solar eclipse (apparently that which took place on 12th May, 361 B.C.),6 and, when this took place as predicted, the tyrant was filled with admiration and made Helicon a present of a talent of silver. This story is, however, not confirmed by any other evidence, and the necessary calculations would have been scarcely less impossible for Helicon than for Thaïes. Martin’s view is that both Thales and Helicon merely explained the cause of solar eclipses and asserted the necessity of their recurrence within certain limits of time, and that these explanations were turned by tradition into predictions. In regard to Thaïes, Martin relies largely on the wording of a passage in Theon of Smyrna, where he purports to quote Eudemus; ‘Eudemus’, he says, ‘relates in his Astronomies that . . . Thaies was the first to discover (
understood) the eclipse of the sun and the fact that the sun’s period with respect to the solstices is not always the same’,7 and the natural meaning of the first part of the sentence is that Thales discovered the explanation and the cause of a solar eclipse. It is true that Diogenes Laertius says that ‘Thales appears, according to some, to have been the first to study astronomy and to predict both solar eclipses and solstices, as Eudemus says in his History of Astronomy’,8 and Diogenes must be quoting from the same passage as Theon; but it is pretty clear, as Martin says, that he copied it inaccurately and himself inserted the word 
referring to predictions; indeed the word ‘predict’ does not go well with ‘solstices’, and is suspect for this reason. Nor does any one credit Thales with having predicted more than one eclipse. No doubt the original passage spoke of ‘eclipses’ and ‘solstices’ in the plural and used some word like ‘discover’ (Theon’s word), not the word ‘predict’. And I think Martin may reasonably argue from the passage of Diogenes that the words ‘according to some’ are Eudemus’s words, not his own, and therefore may be held to show that the truth of the tradition was not beyond doubt.9
Nevertheless, as Tannery observes,10 Martin’s argument can hardly satisfy us so far as it relates to Thales. The evidence that Thales actually predicted a solar eclipse is as conclusive as we could expect for an event belonging to such remote times, for Diogenes Laertius quotes Xenophanes as well as Herodotus as having admired Thales’ achievement, and Xenophanes was almost contemporary with Thales. We must therefore accept the fact as historic, and it remains to inquire in what sense or form, and on what ground, he made his prediction. The accounts of it vary. Herodotus says11 that the Lydians and the Medes continued their war, and ‘when, in the sixth year, they encountered one another, it fell out that, after they had joined battle, the day suddenly turned into night. Now that this transformation of day (into night) would occur was foretold to the Ionians by Thales of Miletus, who fixed as the limit of time this very year in which the change actually took place’.12 The prediction was therefore at best a rough one, since it only specified that the eclipse would occur within a certain year; and the true explanation seems to be that it was a prediction of the same kind as had long been in vogue with the Chaldaeans. That they had a system enabling them to foretell pretty accurately the eclipses of the moon is clear from the fact that some of the eclipses said by Ptolemy13 to have been observed in Babylon were so partial that they could hardly have been noticed if the observers had not been to some extent prepared for them. Three of the eclipses mentioned took place during eighteen months in the years 721 and 720. It is probable that the Chaldaeans arrived at this method of approximately predicting the times at which lunar eclipses would occur by means of the period of 223 lunations, which was doubtless discovered as the result of long-continued observations. This period is mentioned by Ptolemy14 as having been discovered by astronomers ‘still more ancient’ than those whom he calls ‘the ancients’.15 Now, while this method would serve well enough for lunar eclipses, it would very often fail for solar eclipses, because no account was taken of parallax. An excellent illustration of the way in which the system worked is on record; it is taken from a translation of an Assyrian cuneiform inscription, the relevant words being the following :
1. To the king my lord, thy servant Abil-istar.
2. May there be peace to the king my lord. May Nebo and Merodach
3. to the king my lord be favourable. Length of days,
4. health of body and joy of heart may the great gods
5. to the king my lord grant. Concerning the eclipse of the moon
6. of which the king my lord sent to me; in the cities of Akkad,
7. Borsippa, and Nipur, observations
8. they made and then in the city of Akkad
9. we saw part. . . .
10. The observation was made and the eclipse took place.
. . .
17. And when for the eclipse of the sun we made
18. an observation, the observation was made and it did not take place.
19. That which I saw with my eyes to the king my lord
20. I send. This eclipse of the moon
21. which did happen concerns the countries
22. with their god all. Over Syria
23. it closes, the country of Phoenicia,
24. of the Hittites, of the people of Chaldaea,
25. but to the king my lord it sends peace, and according to
26. the observation, not the extending
27. of misfortune to the king my lord
28. may there be.
It would seem, as Tannery says,17 that these clever people knew how to turn their ignorance to account as well as their knowledge. For them it was apparently of less consequence that their predictions should come true than that they should not let an eclipse take place without their having predicted it.18
As it is with Egypt that legend associates Thales, it is natural to ask whether the Egyptians too were acquainted with the period of 223 lunations. We have no direct proof; but Diodorus Siculus says that the priests of Thebes predicted eclipses quite as well as the Chaldeans,19 and it is quite possible that the former had learnt from the latter the period and the notions on which the successful prediction of eclipses depended. It is not, however, essential to suppose that Thales got the information from the Egyptians; he may have obtained it more directly. Lydia was an outpost of Assyrio-Babylonian culture; this is established by (among other things) the fact of the Assyrian protectorate over the kings Gyges and Ardys (attested by cuneiform inscriptions); and ‘no doubt the inquisitive Ionians who visited the gorgeous capital Sardes, situated in their immediate neighbourhood, there first became acquainted with the elements of Babylonian science’.20
If there happened to be a number of possible solar eclipses in the year which (according to Herodotus) Thales fixed, he was not taking an undue risk; but it was great luck that it should have been total.21
Perhaps I have delayed too long over the story of the eclipse; but it furnishes a convenient starting-point for a consideration of the claim of Thales to be credited with the multitude of other discoveries in astronomy attributed to him by the Doxographi and others. First, did he know the cause of eclipses? Aëtius says that he thought the sun was made of an earthy substance,22 like the moon, and was the first to declare that the sun is eclipsed when the moon comes in a direct line below it, the image of the moon then appealing on the sun’s disc as on a mirror;23 and again he says that Thales, as well as Anaxagoras, Plato, Aristotle, and the Stoics, in accord with the mathematicians, held that the moon is eclipsed by reason of its falling into the shadow made by the earth when the earth is between the two heavenly bodies.24 But, as regards the eclipse of the moon, Thales could not have given this explanation, because he held that theearth floated on the water;25 from which it may also be inferred that he, like his successors down to Anaxagoras inclusive, thought the earth to be a disc or a short cylinder. And if he had given the true explanation of the solar eclipse, it is impossible that all the succeeding Ionian philosophers should have exhausted their imaginations in other fanciful explanations such as we find recorded.26
We may assume that Thales would regard the sun and the moon as discs like the earth, or perhaps as hollow bowls which could turn so as to show a dark side.27 We must reject the statements of Aëtius that he was the first to hold that the moon is lit up by the sun, and that it seems to suffer its obscurations each month when it approaches the sun, because the sun illuminates it from one side only.28 For it was Anaxagoras who first gave the true scientific doctrine that the moon is itself opaque but is lit up by the sun, and that this is the explanation no less of the moon’s phases than of eclipses of the sun and moon; when we read in Theon of Smyrna that, according to Eudernus’s History of Astronomy, these discoveries were due to Anaximenes,29 this would seem to be an error, because the Doxographi say nothing of any explanations of eclipses by Anaximenes,30 while on the other hand Aëtius does attribute to him the view that the moon was made of fire,31 just as the sun and stars are made of fire.32
We must reject, so far as Thales is concerned, the traditions that ‘Thales, the Stoics, and their schools, made the earth spherical’,33 and that ‘the school of Thales put the earth in the centre’.34 For (1) we have seen that Thales made the earth a circular or cylindrical disc floating on the water like a log35 or a cork; and (2), so far as we can judge of his conception of the universe, he would appear to have regarded it as a mass of water (that on which the earth floats) with the heavens superposed in the form of a hemisphere and also bounded by the primeval water. It follows from this conception that for Thales the sun, moon, and stars did not, between their setting and rising again, continue their circular path below the earth, but (as with Anaximenes later) laterally round the earth.
Tannery36 compares Thales’ view of the world with that found in the ancient Egyptian papyri. In the beginning existed the Nū, a primordial liquid mass in the limitless depths of which floated the germs of things. When the sun began to shine, the earth was flattened out and the waters separated into two masses. The one gave rise to the rivers and the ocean; the other, suspended above, formed the vault of heaven, the waters above, on which the stars and the gods, borne by an eternal current, began to float. The sun, standing upright in his sacred barque which had endured millions of years, glides slowly, conducted by an army of secondary gods, the planets and the fixed stars. The assumption of an upper and lower ocean is also old-Babylonian (cf. the division in Gen. i. 7 of the waters which were under the firmament from the waters which were above the firmament).
In a passage quoted by Theon of Smyrna, Eudemus attributed to Thales the discovery of ‘the fact that the period of the sun with respect to the solstices is not always the same’.37 The expression is ambiguous, but it must apparently mean the inequality of the length of the four astronomical seasons, that is, the four parts of the tropical year38 as divided by the solstices and the equinoxes. Eudemus referred presumably to the two written works by Thales On the Solstice and On the Equinox,39 which again would seem to be referred to in a later passage of Diogenes Laertius : ‘Lobon of Argos says that his written works extend to 200 verses’. Now Hesiod, in the Works and Days, advises the commencement of certain operations, such as sowing, reaping, and threshing, when particular constellations rise or set in the morning, and he uses the solstices as fixed periods, but does not mention the equinoxes. Tannery40 thinks, therefore, that Thales’ work supplemented Hesiod’s by the addition of other data and, in particular, fixed the equinoxes in the same way as Hesiod had fixed the solstices. The inequality of the intervals between the equinoxes and the solstices in one year would thus be apparent. This explanation agrees with the remark of Pliny that Thales fixed the matutinal setting of the Pleiades on the 25th day from the autumnal equinox.41 All this knowledge Thales probably derived from the Egyptians or the Babylonians. The Babylonians, and doubtless the Egyptians also, were certainly capable of determining more or less roughly the solstices and the equinoxes; and they would doubtless do this by means of the gnomon, the use of which, with that of the polos, the Greeks are said to have learnt from the Babylonians.42
Thales equally learnt from the Egyptians his division of the year into 365 days;43 it is possible also that he followed their arrangement of months of 30 days each, instead of the practice already in his time adopted in Greece of reckoning by lunar months.
The Doxographi associate Thales with Pythagoras and his school as having divided the whole sphere of the heaven by five circles, the arctic which is always visible, the summer-tropical, the equatorial, the winter-tropical, and the antarctic which is always invisible; it is added that the so-called zodiac circle passes obliquely to the three middle circles, touching all three, while the meridian circle, which goes from north to south, is at right angles to all the five circles.44 But, if Thales had any notion of these circles, it must have been of the vaguest; the antarctic circle in particular presupposes the spherical form for the earth, which was not the form which Thales gave it. Moreover, the division into zones is elsewhere specifically attributed to Parmenides and Pythagoras; and, indeed, Parmenides and Pythagoras were the first to be in a position to take this step,45 as they were the first to hold that the earth is spherical in shape. Again, Eudemus is quoted46 as distinctly attributing the discovery of the ‘cincture of the zodiac (circle)’ to Oenopides, who was at least a century later than Thales.
Diogenes Laertius says that, according to some authorities, Thales was the first to declare the apparent size of the sun (and the moon) to be 1/720th part of the circle described by it.47 The version of this story given by Apuleius is worth quoting for a human touch which it contains :
‘The same Thales in his declining years devised a marvellous calculation about the sun, which I have not only learnt but verified by experiment, showing how often the sun measures by its own size the circle which it describes. Thales is said to have communicated this discovery soon after it was made to Mandrolytus of Priene, who was greatly delighted with this new and unexpected information and asked Thales to say how much by way of fee he required to be paid to him for so important a piece of knowledge. “I shall be sufficiently paid”, replied the sage, “if, when you set to work to tell people what you have learnt from me, you will not take credit for it yourself but will name me, rather than another, as the discoverer.”’48
Seeing that in Thales’ system the sun and moon did not pass under the earth and describe a complete circle, he could hardly have stated the result in the precise form in which Diogenes gives it. If, however, he stated its equivalent in some other way, it is again pretty certain that he learnt it from the Egyptians or Babylonians. Cleomedes,49 indeed, says that, by means of a water-clock, we can compare the water which flows out during the time that it takes the sun when rising to get just clear of the horizon with the amount which flows out in the whole day and night; in this way we get a ratio of 1 to 750; and he adds that this method is said to have been first devised by the Egyptians. Again, it has been suggested50 that the Babylonians had already, some sixteen centuries before Christ, observed that the sun takes 1/30th of an hour to rise. This would, on the assumption of 24 hours for a whole day and night, give for the sun’s apparent diameter 1/720th of its circle, the same excellent approximation as that attributed to Thales. But there is the difficulty that, when the Babylonians spoke of 1/30th of an hour in an equinoctial day as being the ‘measure’ 
of the sun’s course, they presumably meant 1/30th of their double-hour, of which there are 12 in a day and night, so that, even if we assume that the measurement of the sun’s apparent diameter was what they meant by 
, the equivalent would be 1°, not 
as Hultsch supposes.51 However, it is difficult to believe that Thales could have made the estimate of 1/720th of the sun’s circle known to the Greeks; if he had, it would be very strange that it should have been mentioned by no one earlier than Archimedes, and that Aristarchus should in the first instance have used the grossly excessive value of 2° which he gives as the angular diameter of the sun and moon in his treatise On the sizes and distances of the sun and moon, and should have been left to discover the value of 
for himself as Archimedes says he did.52
A few more details of Thales’ astronomy are handed down. He said of the Hyades that there are two, one north and the other south.53 According to Callimachus,54 he observed the Little Bear; ‘he was said to have used as a standard [i. e. for finding the pole] the small stars of the Wain, that being the method by which Phoenician navigators steer their course.’ According to Aratus55 the Greeks sailed by the Great Bear, the Phoenicians by the Little Bear. Consequently it would seem that Thales advised the Greeks to follow the Phoenician plan in preference to their own. This use of the Little Bear was probably noted in the handbook under the title of Nautical Astronomy attributed by some to Thales, and by others to Phocus of Samos,56 which was no doubt intended to improve upon the Astronomy in poetical form attributed to Hesiod, as in its turn it was followed by the Astrology of Cleostratus.57
.
consisting of 24 dactyli and equivalent to 2°, it does not follow that the estimate itself is Babylonian. For the same system of expressing angles may have been used by Pytheas and was certainly used by Hipparchus (cf. Strabo, ii. 1. 18, p. 75 Cas., Hipparchi in Aratiet Eudoxi phaenomena coinment. ii. 5. 1, p. 186. 11, Manit., and Ptolemy, Syntaxis vii. 1, vol. ii, pp. 4–8, Heib.).