a history of science-1-第2章
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hing like a full analysis; we may note in passing; not merely what primitive man knew; but what he did not know; that at least a vague notion may be gained of the field for scientific research that lay open for historic man to cultivate。
It must be understood that the knowledge of primitive man; as we are about to outline it; is inferential。 We cannot trace the development of these principles; much less can we say who discovered them。 Some of them; as already suggested; are man's heritage from non…human ancestors。 Others can only have been grasped by him after he had reached a relatively high stage of human development。 But all the principles here listed must surely have been parts of our primitive ancestor's knowledge before those earliest days of Egyptian and Babylonian civilization; the records of which constitute our first introduction to the so…called historical period。 Taken somewhat in the order of their probable discovery; the scientific ideas of primitive man may be roughly listed as follows: 1。 Primitive man must have conceived that the earth is flat and of limitless extent。 By this it is not meant to imply that he had a distinct conception of infinity; but; for that matter; it cannot be said that any one to…day has a conception of infinity that could be called definite。 But; reasoning from experience and the reports of travellers; there was nothing to suggest to early man the limit of the earth。 He did; indeed; find in his wanderings; that changed climatic conditions barred him from farther progress; but beyond the farthest reaches of his migrations; the seemingly flat land…surfaces and water…surfaces stretched away unbroken and; to all appearances; without end。 It would require a reach of the philosophical imagination to conceive a limit to the earth; and while such imaginings may have been current in the prehistoric period; we can have no proof of them; and we may well postpone consideration of man's early dreamings as to the shape of the earth until we enter the historical epoch where we stand on firm ground。 2。 Primitive man must; from a very early period; have observed that the sun gives heat and light; and that the moon and stars seem to give light only and no heat。 It required but a slight extension of this observation to note that the changing phases of the seasons were associated with the seeming approach and recession of the sun。 This observation; however; could not have been made until man had migrated from the tropical regions; and had reached a stage of mechanical development enabling him to live in subtropical or temperate zones。 Even then it is conceivable that a long period must have elapsed before a direct causal relation was felt to exist between the shifting of the sun and the shifting of the seasons; because; as every one knows; the periods of greatest heat in summer and greatest cold in winter usually come some weeks after the time of the solstices。 Yet; the fact that these extremes of temperature are associated in some way with the change of the sun's place in the heavens must; in time; have impressed itself upon even a rudimentary intelligence。 It is hardly necessary to add that this is not meant to imply any definite knowledge of the real meaning of; the seeming oscillations of the sun。 We shall see that; even at a relatively late period; the vaguest notions were still in vogue as to the cause of the sun's changes of position。 That the sun; moon; and stars move across the heavens must obviously have been among the earliest scientific observations。 It must not be inferred; however; that this observation implied a necessary conception of the complete revolution of these bodies about the earth。 It is unnecessary to speculate here as to how the primitive intelligence conceived the transfer of the sun from the western to the eastern horizon; to be effected each night; for we shall have occasion to examine some historical speculations regarding this phenomenon。 We may assume; however; that the idea of the transfer of the heavenly bodies beneath the earth (whatever the conception as to the form of that body) must early have presented itself。 It required a relatively high development of the observing faculties; yet a development which man must have attained ages before the historical period; to note that the moon has a secondary motion; which leads it to shift its relative position in the heavens; as regards the stars; that the stars themselves; on the other hand; keep a fixed relation as regards one another; with the notable exception of two or three of the most brilliant members of the galaxy; the latter being the bodies which came to be known finally as planets; or wandering stars。 The wandering propensities of such brilliant bodies as Jupiter and Venus cannot well have escaped detection。 We may safely assume; however; that these anomalous motions of the moon and planets found no explanation that could be called scientific until a relatively late period。 3。 Turning from the heavens to the earth; and ignoring such primitive observations as that of the distinction between land and water; we may note that there was one great scientific law which must have forced itself upon the attention of primitive man。 This is the law of universal terrestrial gravitation。 The word gravitation suggests the name of Newton; and it may excite surprise to hear a knowledge of gravitation ascribed to men who preceded that philosopher by; say; twenty…five or fifty thousand years。 Yet the slightest consideration of the facts will make it clear that the great central law that all heavy bodies fall directly towards the earth; cannot have escaped the attention of the most primitive intelligence。 The arboreal habits of our primitive ancestors gave opportunities for constant observation of the practicalities of this law。 And; so soon as man had developed the mental capacity to formulate ideas; one of the earliest ideas must have been the conception; however vaguely phrased in words; that all unsupported bodies fall towards the earth。 The same phenomenon being observed to operate on water…surfaces; and no alteration being observed in its operation in different portions of man's habitat; the most primitive wanderer must have come to have full faith in the universal action of the observed law of gravitation。 Indeed; it is inconceivable that he can have imagined a place on the earth where this law does not operate。 On the other hand; of course; he never grasped the conception of the operation of this law beyond the close proximity of the earth。 To extend the reach of gravitation out to the moon and to the stars; including within its compass every particle of matter in the universe; was the work of Newton; as we shall see in due course。 Meantime we shall better understand that work if we recall that the mere local fact of terrestrial gravitation has been the familiar knowledge of all generations of men。 It may further help to connect us in sympathy with our primeval ancestor if we recall that in the attempt to explain this fact of terrestrial gravitation Newton made no advance; and we of to…day are scarcely more enlightened than the man of the Stone Age。 Like the man of the Stone Age; we know that an arrow shot into the sky falls back to the earth。 We can calculate; as he could not do; the arc it will describe and the exact speed of its fall; but as to why it returns to earth at all; the greatest philosopher of to…day is almost as much in the dark as was the first primitive bowman that ever made the experiment。 Other physical facts going to make up an elementary science of mechanics; that were demonstratively known to prehistoric man; were such as these: the rigidity of solids and the mobility of liquids; the fact that changes of temperature transform solids to liquids and vice versathat heat; for example; melts copper and even iron; and that cold congeals water; and the fact that friction; as illustrated in the rubbing together of two sticks; may produce heat enough to cause a fire。 The rationale of this last experiment did not receive an explanation until about the beginning of the nineteenth century of our own era。 But the experimental fact was so well known to prehistoric man that he employed this method; as various savage tribes emp