Читать книгу An Introduction to the History of Science - Walter Libby - Страница 9

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No sooner did the Greeks turn their attention to the sciences which had originated in Egypt and Babylonia than the characteristic intellectual quality of the Hellenic genius revealed itself. Thales (640-546 B.C.), who is usually regarded as the first of the Greek philosophers, was the founder of Greek geometry and astronomy. He was one of the seven "wise men" of Greece, and might be called the Benjamin Franklin of antiquity, for he was interested in commerce, famous for political sagacity, and honored for his disinterested love of general truth. His birthplace was Miletus, a Greek city on the coast of Asia Minor. There is evidence that he acquired a knowledge of Babylonian astronomy. The pursuit of commerce carried him to Egypt, and there he gained a knowledge of geometry. Not only so, but he was able to advance this study by generalizing and formulating its truths. For the Egyptians, geometry was concerned with surfaces and dimensions, with areas and cubical contents; for the Greek, with his powers of abstraction, it became a study of line and angle. For example, Thales saw that the angles at the base of an isosceles triangle are equal, and that when two straight lines cut one another the vertically opposite angles are equal. However, after having established general principles, he showed himself capable of applying them to the solution of particular problems. In the presence of the Egyptian priests, to which class he was solely indebted for instruction, Thales demonstrated a method of measuring the height of a pyramid by reference to its shadow. And again, on the basis of his knowledge of the relation of the sides of a triangle to its angles, he developed a practical rule for ascertaining the distance of a ship from the shore.

The philosophical mind of Thales laid hold, no doubt, of some of the essentials of astronomical science. The particulars usually brought forward to prove his originality tend rather to show his indebtedness to the Babylonians. The number of days in the year, the length of the synodic month, the relation of the sun's apparent diameter to the ecliptic, the times of recurrence of eclipses, were matters that had long been known to the Babylonians, as well as to the Chinese. However, he aroused great interest in astronomy among the Greeks by the prediction of a solar eclipse. This was probably the eclipse of 585 B.C., which interrupted a fierce battle between the Medes and the Lydians. The advice of Thales to mariners to steer by the Lesser Bear, as nearer the pole, rather than by the Great Bear, shows also that in his astronomical studies as in his geometrical he was not indifferent to the applications of scientific knowledge.

In fact, some writers maintain that Thales was not a philosopher at all, but rather an astronomer and engineer. We know very little of his purely speculative thought. We do know, however, that he arrived at a generalization—fantastic to most minds—that all things are water. Attempts have been made to add to this statement, and to explain it away. Its great interest for the history of thought lies in the fact that it is the result of seeking the constant in the variable, the unitary principle in the multiple phenomena of nature. This abstract and general view (though perhaps suggested by the Babylonian belief that the world originated in a watery chaos, or by the teaching of Egyptian priests) was preëminently Greek, and was the first of a series of attempts to discover the basis or origin of all things. One of the followers of Thales taught that air was the fundamental principle; while Heraclitus, anticipating to some extent modern theories of the origin of the cosmos, declared in favor of a fiery vapor subject to ceaseless change. Empedocles, the great philosopher-physician, first set forth the doctrine of the four elements—earth, air, fire, and water. For Democritus indivisible particles or atoms are fundamental to all phenomena. It is evident that the theory of Thales was a starting point for Greek abstract thought, and that his inclination to seek out principles and general laws accounts for his influence on the development both of philosophy and the sciences.

Pythagoras, on the advice of Thales, visited Egypt in the pursuit of mathematics. There is reason to believe that he also visited Babylonia. For him and his followers mathematics became a philosophy—almost a religion. They had discovered (by experimenting with the monochord, the first piece of physical-laboratory apparatus, consisting of a tense harpstring with a movable bridge) the effect on the tone of the string of a musical instrument when the length is reduced by one half, and also that strings of like thickness and under equal tension yield harmonious tones when their lengths are related as 1:2, 2:3, 3:4, 4:5. The Pythagoreans drew from this the extravagant inference that the heavenly bodies would be in distance from the earth as 1, 2, 3, 4, 5, etc. Much of their theory must seem to the modern mind merely fanciful and unsupported speculation. At the same time it is only just to this school of philosophers to recognize that their assumption that simple mathematical relationships govern the phenomena of nature has had an immense influence on the advance of the sciences. Whether their fanaticism for number was owing to the influence of Egyptian priests or had an Oriental origin, it gave to the Pythagoreans an enthusiasm for pure mathematics. They disregarded the bearing of their science on the practical needs of life. Old problems like squaring the circle, trisecting the angle, and doubling the cube, were now attempted in a new spirit and with fresh vigor. The first, second, and fourth books of Euclid are largely of Pythagorean origin. For solid geometry as a science we are also indebted to this sect of number-worshipers. One of them (Archytas, 428-347 B.C., a friend of Plato) was the first to apply geometry to mechanics. We see again here, as in the case of Thales, that the love of abstract thought, the pursuit of science as science, did not interfere with ultimate practical applications.

Plato (429-347 B.C.), like many other Greek philosophers, traveled extensively, visiting Asia Minor, Egypt, and Lower Italy, where Pythagorean influence was particularly strong. His chief interest lay in speculation. For him there were two worlds, the world of sense and the world of ideas. The senses deceive us; therefore, the philosopher should turn his back upon the world of sensible impressions, and develop the reason. In his Dialogues he outlined a course of training and study, the professed object of which was to educate a class of philosophers. (Strange to say, Plato's curriculum, planned originally for the intellectual élite, still dictates in our schools the education of millions of boys and girls whose careers do not call for a training merely of the reason.)

Over the porch of his school, the Academy at Athens, were inscribed the words, "Let no one who is unacquainted with geometry enter here." It was not because it was useful in everyday life that Plato laid such insistence on this study, but because it increased the students' powers of abstraction and trained the mind to correct and vigorous thinking. From his point of view the chief good of geometry is lost unless we can through it withdraw the mind from the particular and the material. He delighted in clearness of conception. His main scientific interest was in astronomy and mathematics. We owe to him the definition of a line as "length without breadth," and the formulation of the axiom, "Equals subtracted from equals leave equals."

Plato had an immediate influence in stimulating mathematical studies, and has been called a maker of mathematicians. Euclid, who was active at Alexandria toward the end of the fourth century B.C., was not one of Plato's immediate disciples but shared the great philosopher's point of view. The story is told that one of his pupils, arrived perhaps at the pons asinorum, asked, "What do I get by learning these things?" Euclid, calling his servant, said, "Give him sixpence, since he must make gain out of what he learns." Adults were also found, even among the nimble-witted Greeks, to whom abstract reasoning was not altogether congenial. This is attested by the familiar story of Ptolemy, King of Egypt, who once asked Euclid whether geometry could not be learned in some easier way than by studying the geometer's book, The Elements. To this the schoolmaster replied, "There is no royal road to geometry." For the academic intelligence abstract and abstruse mathematics are tonic and an end in themselves. As already stated, their ultimate practical value is also immense. One of Plato's associates, working under his direction, investigated the curves produced by cutting cones of different kinds in a certain plane. These curves—the ellipse, the parabola, hyperbola—play a large part in the subsequent history of astronomy and mechanics. Another Platonist made the first measurement of the earth's circumference.

Aristotle, the greatest pupil of Plato, was born at Stagira in 384 B.C. He came of a family of physicians, was trained for the medical profession, and had his attention early directed to natural phenomena. He entered the Academy at Athens about 367 B.C., and studied there till the death of Plato twenty years later. He was a diligent but, as was natural, considering the character of his early education, by no means a passive student. Plato said that Aristotle reacted against his instructor as a vigorous colt kicks the mother that nourishes it. The physician's son did not accept without modification the view that the philosopher should turn his back upon the things of sense. He had been trained in the physical science of the time, and believed in the reality of concrete things. At the same time he absorbed what he found of value in his master's teachings. He thought that science did not consist in a mere study of individual things, but that we must pass on to a formulation of general principles and then return to a study of the concrete. His was a great systematizing intellect, which has left its imprint on nearly every department of knowledge. Physical astronomy, physical geography, meteorology, physics, chemistry, geology, botany, anatomy, physiology, embryology, and zoölogy were enriched by his teaching. It was through him that logic, ethics, psychology, rhetoric, æsthetics, political science, zoölogy (especially ichthyology), first received systematic treatment. As a great modern philosopher has said, Aristotle pressed his way through the mass of things knowable, and subjected its diversity to the power of his thought. No wonder that for ages he was known as "The Philosopher," master of those who know. His purpose was to comprehend, to define, to classify the phenomena of organic and inorganic nature, to systematize the knowledge of his own time.

Twenty years' apprenticeship in the school of Plato had sharpened his logical powers and added to his stock of general ideas, but had not taught him to distrust his senses. When we say that our eyes deceive us, we really confess that we have misinterpreted the data that our sight has furnished. Properly to know involves the right use of the senses as well as the right use of reason. The advance of science depends on the development both of speculation and observation. Aristotle advised investigators to make sure of the facts before seeking the explanation of the facts. Where preconceived theory was at variance with observed facts, the former must of course give way. Though it has been said that while Plato was a dreamer, Aristotle was a thinker, yet it must be acknowledged in qualification that Plato often showed genuine knowledge of natural phenomena in anatomy and other departments of study, and that Aristotle was carried away at times by his own presuppositions, or failed to bring his theories to the test of observation. The Stagirite held that the velocity of falling bodies is proportional to their weight, that the function of the diaphragm is to divide the region of the nobler from that of the animal passions, and that the brain is intended to act in opposition to the heart, the brain being formed of earthy and watery material, which brings about a cooling effect. The theory of the four elements—the hot, the cold, the moist, the dry—led to dogmatic statements with little attempt at verification. From the standpoint of modern studies it is easy to point out the mistakes of Aristotle even. Science is progressive, not infallible.

In his own time he was rather reproached for what was considered an undignified and sordid familiarity with observed facts. His critics said that having squandered his patrimony, he had served in the army, and, failing there, had become a seller of drugs. His observations on the effects of heat seem to have been drawn from the common processes of the home and the workshop. Even in the ripening of fruits heat appears to him to have a cooking effect. Heat distorts articles made of potters' clay after they have been hardened by cold. Again we find him describing the manufacture of potash and of steel. He is not disdainful of the study of the lower animals, but invites us to investigate all forms in the expectancy of discovering something natural and beautiful. In a similar spirit of scientific curiosity the Aristotelian work The Problems studies the principle of the lever, the rudder, the wheel and axle, the forceps, the balance, the beam, the wedge, as well as other mechanical principles.

In Aristotle, in fact, we find a mind exceptionally able to form clear ideas, and at the same time to observe the rich variety of nature. He paid homage both to the multiplicity and the uniformity of nature, the wealth of the phenomena and the simplicity of the law explaining the phenomena. Many general and abstract ideas (category, energy, entomology, essence, mean between extremes, metaphysics, meteorology, motive, natural history, principle, syllogism) have through the influence of Aristotle become the common property of educated people the world over.

Plato was a mathematician and an astronomer. Aristotle was first and foremost a biologist. His books treated the history of animals, the parts of animals, the locomotion of animals, the generation of animals, respiration, life and death, length and shortness of life, youth and old age. His psychology is, like that of the present day, a biological psychology. In his contributions to biological science is manifested his characteristic inclination to be at once abstract and concrete. His works display a knowledge of over five hundred living forms. He dissected specimens of fifty different species of animals. One might mention especially his minute knowledge of the sea-urchin, of the murex (source of the famous Tyrian dye), of the chameleon, of the habits of the torpedo, the so-called fishing-frog, and nest-making fishes, as well as of the manner of reproduction of whales and certain species of sharks. One of his chief contributions to anatomy is the description of the heart and of the arrangement of the blood-vessels. A repugnance to the dissection of the human body seems to have checked to some extent his curiosity in reference to the anatomy of man, but he was acquainted with the structure of the internal ear, the passage leading from the pharynx to the middle ear, and the two outer membranes of the brain of man. Aristotle's genius did not permit him to get lost in the mere details of observed phenomena. He recognized resemblances and differences between the various species, classified animals as belonging to two large groups, distinguished whales and dolphins from fishes, recognized the family likeness of the domestic pigeon, the wood pigeon, the rock pigeon, and the turtle dove. He laid down the characteristics of the class of invertebrates to which octopus and sepia belong. Man takes a place in Aristotle's system of nature as a social animal, the highest type of the whole series of living beings, characterized by certain powers of recall, reason, deliberation. Of course it was not to be expected that Aristotle should work out a fully satisfactory classification of all the varieties of plants and animals known to him. Yet his purpose and method mark him as the father of natural science. He had the eye to observe and the mind to grasp the relationships and the import of what he observed. His attempt to classify animals according to the nature of their teeth (dentition) has been criticized as unsuccessful, but this principle of classification is still of use, and may be regarded as typical of his mind, at once careful and comprehensive.

One instance of Aristotle's combining philosophical speculation with acute observation of natural phenomena is afforded by his work on generation and development. He knew that the transmission of life deserves special study as the predominant function of the various species of plants and animals. Deformed parents may have well-formed offspring. Children may resemble grandparents rather than parents. It is only toward the close of its development that the embryo exhibits the characteristics of its parent species. Aristotle traced with some care the embryological development of the chick from the fourth day of incubation. His knowledge of the propagation of animals was, however, not sufficient to make him reject the belief in spontaneous generation from mud, sand, foam, and dew. His errors are readily comprehensible, as, for example, in attributing spontaneous generation to eels, the habits and mode of reproduction of which only recent studies have made fully known. In regard to generation, as in other scientific fields, the philosophic mind of Aristotle anticipated modern theories, and also raised general questions only to be solved by later investigation of the facts.

Only one indication need be given of the practical results that flowed from Aristotle's scientific work. In one of his writings he has stated that the sphericity of the earth can be observed from the fact that its shadow on the moon at the time of eclipse is an arc. That it is both spherical and small in comparison with the heavenly bodies appears, moreover, from this, that stars visible in Egypt are invisible in countries farther north; while stars always above the horizon in northern countries are seen to set from countries to the south. Consequently the earth is not only spherical but also not large; otherwise this phenomenon would not present itself on so limited a change of position on the part of the observer. "It seems, therefore, not incredible that the region about the Pillars of Hercules [Gibraltar] is connected with that of India, and that there is thus only one ocean." It is known that this passage from The Philosopher influenced Columbus in his undertaking to reach the Orient by sailing west from the coast of Spain.

We must pass over Aristotle's observation of a relationship (homology) between the arms of man, the forelegs of quadrupeds, the wings of birds, and the pectoral fins of fishes, as well as many other truths to which his genius for generalization led him.

In the field of botany Aristotle had a wide knowledge of natural phenomena, and raised general questions as to mode of propagation, nourishment, relation of plants to animals, etc. His pupil and lifelong friend, and successor as leader of the Peripatetic school of philosophy, Theophrastus, combined a knowledge of mathematics, astronomy, botany, and mineralogy. His History of Plants describes about five hundred species. At the same time he treats the general principles of botany, the distribution of plants, the nourishment of the plant through leaf as well as root, the sexuality of date palm and terebinth. He lays great stress on the uses of plants. His classification of plants is inferior to Aristotle's classification of animals. His views in reference to spontaneous generation are more guarded than those of his master. His work On Stones is dominated by the practical rather than the generalizing spirit. It is evidently inspired by a knowledge of mines, such as the celebrated Laurium, from which Athens drew its supply of silver, and the wealth from which enabled the Athenians to develop a sea-power that overmatched that of the Persians. Even to-day enough remains of the galleries, shafts, scoria, mine-lamps, and other utensils to give a clear idea of this scene of ancient industry. Theophrastus considered the medicinal uses of minerals as well as of plants.

We have failed to mention Hippocrates (460-370 B.C.), the Father of Medicine, in whom is found an intimate union of practical science and speculative philosophy. We must also pass over such later Greek scientists as Aristarchus and Hipparchus who confuted the theories of Pythagoras and Plato in reference to the relative distances of the heavenly bodies from the earth. Archimedes of Syracuse demands, however, particular consideration. He lived in the third century B.C., and has been called the greatest mathematician of antiquity. In him we find the devotion to the abstract that marked the Greek intelligence. He went so far as to say that every kind of art is ignoble if connected with daily needs. His interest lay in abstruse mathematical problems. His special pride was in having determined the relative dimensions of the sphere and the enclosing cylinder. He worked out the principle of the lever. "Give me," he said, "a place on which to stand and I will move the earth." He approximated more closely than the Egyptians the solution of the problem of the relation between the area of a circle and the radius. His work had practical value in spite of himself. At the request of his friend the King of Sicily, he applied his ingenuity to discover whether a certain crown were pure gold or alloyed with silver, and he hit upon a method which has found many applications in the industries. His name is associated with the endless screw. In fact, his practical contrivances won such repute that it is not easy to separate the historical facts from the legends that enshroud his name. He aided in the defense of his native city against the Romans in 212 B.C., and devised war-engines with which to repel the besiegers. After the enemy had entered the city, says tradition, he stood absorbed in a mathematical problem which he had diagrammed on the sand. As a rude Roman soldier approached, Archimedes cried, "Don't spoil my circles," and was instantly killed. The victorious general, however, buried him with honor, and on the tomb of the mathematician caused to be inscribed the sphere with its enclosing cylinder. The triumphs of Greek abstract thought teach the lesson that practical men should pay homage to speculation even when they fail to comprehend a fraction of it.