below the moon's sphere is subject to continual change, and motions within it are in general rectilinear — a theory destined long to block progress in mechanics. Of the four elements, earth is nearest the centre, water comes next, fire and air form the atmosphere, fire, predominating in the upper part, air in the lower. In this region of fire are generated shooting stars, auroras, and comets, the latter consisting of ignited vapors, such as constitute the Milky Way. Against any orbital motion of the earth Aristotle urges the absence of any apparent displacement of the stars. Reviewing his astronomical theories, Dreyer says: His careful and critical examination of the opinions of previous philosophers makes us regret all the more that his search for the causes of phenomena was often a mere search among words, a series of vague and loose attempts to find what was 'according to nature' and what was not; and even though he professed to found his speculations on facts, he failed to free his discussion of these from purely metaphysical and preconceived notions. It is, however, easy to understand the great veneration in which his voluminous writings on natural science were held for so many centuries, for they were the first, and for many centuries the only, attempt to systematize the whole amount of knowledge of nature accessible to mankind; while the tendency to seek for the principles of natural philosophy by considering the meaning of the words ordinarily used to describe the phenomena of nature, which to us is his great defect, appealed strongly to the medieval mind, and, unfortunately, finally helped to retard the development of science in the days of Copernicus and Galileo. At times Aristotle shows consciousness that his theories are based on inadequate knowledge of facts. "The phenomena are not yet sufficiently investigated. When they once shall be, then one must trust more to observation than to speculation, and to the latter no farther than it agrees with the phenomena.' An astronomer' he says 'must be the wisest of men; his mind must be duly disciplined in youth; especially is mathematical study necessary; both an acquaintance with the doctrine of number, and also with that other branch of mathematics, which, closely connected as it is with the science of the heavens, we very absurdly call geometry, the measurement of the earth.' Aristotle's writings include not merely works on scientific subjects, but treatises of the very first importance On Poetry, On Rhetoric, On Metaphysics, On Ethics, and On Politics. Besides his scientific works mentioned above, there are others entitled On Generation and Destruction, On the Parts of Animals, On Generation of Animals, Researches about Animals, On the Locomotion of Animals. One of the most important of his many services to science is the encyclopedic character of his writings, since from time to time he reviews in them the opinions of his predecessors whose works are sometimes known to us chiefly through his references to them. While standing thus upon the shoulders of the past, he shows at the same time both vast learning and much originality. He may be truly called the founder of zoölogy. Of Aristotle's contributions to science, the greatest was unquestionably that spirit of curiosity, of inquiry, of scepticism, and of veracity which he brought to bear on everything about him and within him. His observations are often poor, his conclusions often erroneous, but his interest, his curiosity, his zeal are indefatigable. THEOPHRASTUS. - One of Aristotle's principal pupils, and his successor in his School, was Theophrastus (372-287 B.C.) notable in the history of science chiefly as an early student of plants, and writer of the most important treatises of antiquity on botany. These were two large works, one of ten books and the other of eight, On the History of Plants, and On the Causes of Plants, respectively. In these, more than 500 species of plants are described, chiefly with reference to their medicinal uses. It is especially interesting to note that Theophrastus recognized the existence of sex in plants, though he does not appear to have known the sex organs. - EPICURUS AND EPICUREANISM. A few words may be said of another philosopher of the fourth century, a follower to some extent of Democritus and the forerunner and exemplar of the Roman Lucretius. This was Epicurus (342-270 B.C.), who, born in Samos and educated in Athens and Asia Minor, became a famous teacher and the head of a remarkable community "such as the ancient world had never seen." The mode of life in this community was not that of the so-called "epicures" of to-day, but very plain, water the general drink, and barley bread the general food. The magnetic personality of Epicurus held the community together, and his chief work was a treatise on Nature in thirty-seven books. Epicureanism is of interest in the history of science chiefly because of its effect on its Roman exponent, the poet Lucretius. Much of it was even a negation of science and the scientific spirit. HERACLIDES. ROTATION OF THE EARTH.-To Heraclides of Pontus in the fourth century B.C. belongs the distinction of teaching that the earth turns on its own axis from west to east in 24 hours. He had been connected with the Pythagoreans, and with the schools of Plato and Aristotle. His work is known to us only indirectly, none of his own writings having survived. He is said also to have advanced the hypothesis that Venus and Mercury revolve about the sun, being therefore at a distance from the earth sometimes greater than the sun, sometimes less. Geminus writing in the first half of the first century B.C. of the different fields and points of view of astronomers and physicists, remarks: For why do sun, moon and planets appear to move unequally? Because, when we assume their circles to be excentric, or the stars to move on an epicycle, the appearing anomaly can be accounted for, and it is necessary to investigate in how many ways the phenomena can be represented, so that the theory of the wandering stars may be made to agree with the etiology in a possible manner. Therefore also a certain Heraclides of Pontus stood up and said that also when the earth moved in some way and the sun stood still in some way, could the irregularity observed relatively to the sun be accounted for. In general it is not the astronomer's business to see what by its nature is immovable and of what kind the moved things are, but framing hypotheses as to some things being in motion and others being fixed, he considers which hypotheses are in conformity with the phenomena in the heavens. He must accept as his principles from the physicist, that the motions of the stars are simple, uniform, and regular, of which he shows that the revolutions are circular, some along parallels, some along oblique circles. This contrast between the physical phenomena and the mathematical theory which corresponds with them, without being true or perhaps even possible in all respects, is of continued and increasing importance in the history of science, as a larger stock of facts was accumulated and as theories still imperfect were more frequently subjected to critical comparison with observed data, instead of being accepted on purely philosophical or metaphysical grounds. Heraclides is not credited with any conception of orbital or progressive motion of the earth. REFERENCES FOR READING ALLMAN. Greek Geometry, Chapters III-IX. ARISTOTLE. On the Parts of Animals, On Generation, etc. BUTCHER, S. H. Aspects of the Greek Genius, Chapter I. BERRY. History of Astronomy, Chapter II, pp. 26–33. DREYER. Planetary System, Chapters III-V. FREEMAN, K. E. Schools of Hellas. GARRISON, F. H. A History of Medicine. (For Hippocrates of Cos.) Gow. History of Greek Mathematics, Chapter VI, Articles 97-116. CHAPTER V GREEK SCIENCE IN ALEXANDRIA There is an astonishing imagination, even in the science of mathematics.... We repeat, there was far more imagination in the head of Archimedes than in that of Homer. Voltaire. If the Greeks had not cultivated Conic Sections, Kepler could not have superseded Ptolemy; if the Greeks had cultivated Dynamics, Kepler might have anticipated Newton. Whewell. If we compare a mathematical problem with an immense rock, whose interior we wish to penetrate, then the work of the Greek mathematicians appears to us like that of a robust stonecutter, who, with indefatigable perseverance, attempts to demolish the rock gradually from the outside by means of hammer and chisel; but the modern mathematician resembles an expert miner, who first constructs a few passages through the rock and then explodes it with a single blast, bringing to light its inner treasures. - Hankel. THE MUSEUM AT ALEXANDRIA. — The subjugation of Greece by Alexander the Great in 330 B.C. checked the further development of Greek civilization on its native soil. After Alexander's death in 323, his vast empire was divided among his generals, and Alexandria, the new Egyptian capital, fell to the lot of Ptolemy. The city as such was then barely ten years old, but very soon became, under the rule of the Ptolemies, the centre of the learned world. By 300 B.C. the Museum (Seat of the Muses) was founded, becoming in effect a veritable university of Greek learning. To this were attached a great library, a dining hall, and lecturerooms for professors. Here for the next 700 years Greek science had its chief abiding place. The fame of Alexandria soon outshone and eventually eclipsed that of Athens, while Romans journeyed from Rome - never important in ancient times as a |