Читать книгу A History of Science (Vol. 1-5) - Edward Huntington Williams - Страница 10

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Herodotus, the Father of History, tells us that once upon a time—which time, as the modern computator shows us, was about the year 590 B.C.—a war had risen between the Lydians and the Medes and continued five years. "In these years the Medes often discomfited the Lydians and the Lydians often discomfited the Medes (and among other things they fought a battle by night); and yet they still carried on the war with equally balanced fortitude. In the sixth year a battle took place in which it happened, when the fight had begun, that suddenly the day became night. And this change of the day Thales, the Milesian, had foretold to the Ionians, laying down as a limit this very year in which the change took place. The Lydians, however, and the Medes, when they saw that it had become night instead of day, ceased from their fighting and were much more eager, both of them, that peace should be made between them."

This memorable incident occurred while Alyattus, father of Croesus, was king of the Lydians. The modern astronomer, reckoning backward, estimates this eclipse as occurring probably May 25th, 585 B.C. The date is important as fixing a mile-stone in the chronology of ancient history, but it is doubly memorable because it is the first recorded instance of a predicted eclipse. Herodotus, who tells the story, was not born until about one hundred years after the incident occurred, but time had not dimmed the fame of the man who had performed the necromantic feat of prophecy. Thales, the Milesian, thanks in part at least to this accomplishment, had been known in life as first on the list of the Seven Wise Men of Greece, and had passed into history as the father of Greek philosophy. We may add that he had even found wider popular fame through being named by Hippolytus, and then by Father aesop, as the philosopher who, intent on studying the heavens, fell into a well; "whereupon," says Hippolytus, "a maid-servant named Thratta laughed at him and said, 'In his search for things in the sky he does not see what is at his feet.'"

Such citations as these serve to bring vividly to mind the fact that we are entering a new epoch of thought. Hitherto our studies have been impersonal. Among Egyptians and Babylonians alike we have had to deal with classes of scientific records, but we have scarcely come across a single name. Now, however, we shall begin to find records of the work of individual investigators. In general, from now on, we shall be able to trace each great idea, if not to its originator, at least to some one man of genius who was prominent in bringing it before the world. The first of these vitalizers of thought, who stands out at the beginnings of Greek history, is this same Thales, of Miletus. His is not a very sharply defined personality as we look back upon it, and we can by no means be certain that all the discoveries which are ascribed to him are specifically his. Of his individuality as a man we know very little. It is not even quite certain as to where he was born; Miletus is usually accepted as his birthplace, but one tradition makes him by birth a Phenician. It is not at all in question, however, that by blood he was at least in part an Ionian Greek. It will be recalled that in the seventh century B.C., when Thales was born—and for a long time thereafter—the eastern shores of the aegean Sea were quite as prominently the centre of Greek influence as was the peninsula of Greece itself. Not merely Thales, but his followers and disciples, Anaximander and Anaximenes, were born there. So also was Herodotas, the Father of History, not to extend the list. There is nothing anomalous, then, in the fact that Thales, the father of Greek thought, was born and passed his life on soil that was not geographically a part of Greece; but the fact has an important significance of another kind. Thanks to his environment, Thales was necessarily brought more or less in contact with Oriental ideas. There was close commercial contact between the land of his nativity and the great Babylonian capital off to the east, as also with Egypt. Doubtless this association was of influence in shaping the development of Thales's mind. Indeed, it was an accepted tradition throughout classical times that the Milesian philosopher had travelled in Egypt, and had there gained at least the rudiments of his knowledge of geometry. In the fullest sense, then, Thales may be regarded as representing a link in the chain of thought connecting the learning of the old Orient with the nascent scholarship of the new Occident. Occupying this position, it is fitting that the personality of Thales should partake somewhat of mystery; that the scene may not be shifted too suddenly from the vague, impersonal East to the individualism of Europe.

All of this, however, must not be taken as casting any doubt upon the existence of Thales as a real person. Even the dates of his life—640 to 546 B.C.—may be accepted as at least approximately trustworthy; and the specific discoveries ascribed to him illustrate equally well the stage of development of Greek thought, whether Thales himself or one of his immediate disciples were the discoverer. We have already mentioned the feat which was said to have given Thales his great reputation. That Thales was universally credited with having predicted the famous eclipse is beyond question. That he actually did predict it in any precise sense of the word is open to doubt. At all events, his prediction was not based upon any such precise knowledge as that of the modern astronomer. There is, indeed, only one way in which he could have foretold the eclipse, and that is through knowledge of the regular succession of preceding eclipses. But that knowledge implies access on the part of some one to long series of records of practical observations of the heavens. Such records, as we have seen, existed in Egypt and even more notably in Babylonia. That these records were the source of the information which established the reputation of Thales is an unavoidable inference. In other words, the magical prevision of the father of Greek thought was but a reflex of Oriental wisdom. Nevertheless, it sufficed to establish Thales as the father of Greek astronomy. In point of fact, his actual astronomical attainments would appear to have been meagre enough. There is nothing to show that he gained an inkling of the true character of the solar system. He did not even recognize the sphericity of the earth, but held, still following the Oriental authorities, that the world is a flat disk. Even his famous cosmogonic guess, according to which water is the essence of all things and the primordial element out of which the earth was developed, is but an elaboration of the Babylonian conception.

When we turn to the other field of thought with which the name of Thales is associated—namely, geometry—we again find evidence of the Oriental influence. The science of geometry, Herodotus assures us, was invented in Egypt. It was there an eminently practical science, being applied, as the name literally suggests, to the measurement of the earth's surface. Herodotus tells us that the Egyptians were obliged to cultivate the science because the periodical inundations washed away the boundary-lines between their farms. The primitive geometer, then, was a surveyor. The Egyptian records, as now revealed to us, show that the science had not been carried far in the land of its birth. The Egyptian geometer was able to measure irregular pieces of land only approximately. He never fully grasped the idea of the perpendicular as the true index of measurement for the triangle, but based his calculations upon measurements of the actual side of that figure. Nevertheless, he had learned to square the circle with a close approximation to the truth, and, in general, his measurement sufficed for all his practical needs. Just how much of the geometrical knowledge which added to the fame of Thales was borrowed directly from the Egyptians, and how much he actually created we cannot be sure. Nor is the question raised in disparagement of his genius. Receptivity is the first prerequisite to progressive thinking, and that Thales reached out after and imbibed portions of Oriental wisdom argues in itself for the creative character of his genius. Whether borrower of originator, however, Thales is credited with the expression of the following geometrical truths:

1. That the circle is bisected by its diameter.

2. That the angles at the base of an isosceles triangle are equal.

3. That when two straight lines cut each other the vertical opposite angles are equal.

4. That the angle in a semicircle is a right angle.

5. That one side and one acute angle of a right-angle triangle determine the other sides of the triangle.

It was by the application of the last of these principles that Thales is said to have performed the really notable feat of measuring the distance of a ship from the shore, his method being precisely the same in principle as that by which the guns are sighted on a modern man-of-war. Another practical demonstration which Thales was credited with making, and to which also his geometrical studies led him, was the measurement of any tall object, such as a pyramid or building or tree, by means of its shadow. The method, though simple enough, was ingenious. It consisted merely in observing the moment of the day when a perpendicular stick casts a shadow equal to its own length. Obviously the tree or monument would also cast a shadow equal to its own height at the same moment. It remains then but to measure the length of this shadow to determine the height of the object. Such feats as this evidence the practicality of the genius of Thales. They suggest that Greek science, guided by imagination, was starting on the high-road of observation. We are told that Thales conceived for the first time the geometry of lines, and that this, indeed, constituted his real advance upon the Egyptians. We are told also that he conceived the eclipse of the sun as a purely natural phenomenon, and that herein lay his advance upon the Chaldean point of view. But if this be true Thales was greatly in advance of his time, for it will be recalled that fully two hundred years later the Greeks under Nicias before Syracuse were so disconcerted by the appearance of an eclipse, which was interpreted as a direct omen and warning, that Nicias threw away the last opportunity to rescue his army. Thucydides, it is true, in recording this fact speaks disparagingly of the superstitious bent of the mind of Nicias, but Thucydides also was a man far in advance of his time.

All that we know of the psychology of Thales is summed up in the famous maxim, "Know thyself," a maxim which, taken in connection with the proven receptivity of the philosopher's mind, suggests to us a marvellously rounded personality.

The disciples or successors of Thales, Anaximander and Anaximenes, were credited with advancing knowledge through the invention or introduction of the sundial. We may be sure, however, that the gnomon, which is the rudimentary sundial, had been known and used from remote periods in the Orient, and the most that is probable is that Anaximander may have elaborated some special design, possibly the bowl-shaped sundial, through which the shadow of the gnomon would indicate the time. The same philosopher is said to have made the first sketch of a geographical map, but this again is a statement which modern researches have shown to be fallacious, since a Babylonian attempt at depicting the geography of the world is still preserved to us on a clay tablet. Anaximander may, however, have been the first Greek to make an attempt of this kind. Here again the influence of Babylonian science upon the germinating Western thought is suggested.

It is said that Anaximander departed from Thales's conception of the earth, and, it may be added, from the Babylonian conception also, in that he conceived it as a cylinder, or rather as a truncated cone, the upper end of which is the habitable portion. This conception is perhaps the first of these guesses through which the Greek mind attempted to explain the apparent fixity of the earth. To ask what supports the earth in space is most natural, but the answer given by Anaximander, like that more familiar Greek solution which transformed the cone, or cylinder, into the giant Atlas, is but another illustration of that substitution of unwarranted inference for scientific induction which we have already so often pointed out as characteristic of the primitive stages of thought.

Anaximander held at least one theory which, as vouched for by various copyists and commentators, entitles him to be considered perhaps the first teacher of the idea of organic evolution. According to this idea, man developed from a fishlike ancestor, "growing up as sharks do until able to help himself and then coming forth on dry land."(1) The thought here expressed finds its germ, perhaps, in the Babylonian conception that everything came forth from a chaos of waters. Yet the fact that the thought of Anaximander has come down to posterity through such various channels suggests that the Greek thinker had got far enough away from the Oriental conception to make his view seem to his contemporaries a novel and individual one. Indeed, nothing we know of the Oriental line of thought conveys any suggestion of the idea of transformation of species, whereas that idea is distinctly formulated in the traditional views of Anaximander.