through the times to come. It combined experiment with calculation, effecting thus a passage from the particular instance to the general law: which should always be confirmed by a constant comparison of results. For example, as he says in his Two New Sciences: "Let us take this at present as a Postulatum, the truth whereof we shall afterwards find established, when we see other conclusions, built upon this Hypothesis, to answer and most exactly agree with Experience." 22

After Galileo it became difficult for an intelligent man not to abandon the old for the new system; yet Milton still held them in the balance! He was predominantly a poet! Galileo died in 1642, and the next year Isaac Newton was born. Between the periods of their working lives, men younger than Galileo but older than Newton made important contributions to the knowledge of the celestial bodies and of the earth in its relations to them. The minds of scientific men became accustomed to the new conceptions, and were disposed to assume their truth.

Newton's greatest creative period extends from his graduation at Cambridge in 1665 to the publication of the Principia in 1687. Though there was no longer call for arguments to prove the general truth of the Copernican. theory, there was still need to rationalize it, and, so to speak, push back its why and wherefore to a further satisfying generalization sounding in some explanatory motive principle.

This was supplied by Newton. Kepler had realized that the planetary motions could not be due to some central point, but must be ascribed to the influence of a central body, to wit, the sun. Galileo showed that the motion of a body goes on in a straight line until stopped or deflected; and also demonstrated the law of accelerated motion in falling bodies. Others pointed out the centrifugal tendency of any body actually revolving around a central point, a principle which when adjusted with Galileo's law of accelerated motion in falling bodies, re

22 Two New Sciences, p. 255 (Weston's translation). Cited by Berry, Hist. of Astronomy, p. 178.

sults in the principle of acceleration directed toward a centre. After them came Newton.

Assuming Galileo's first law that a body in motion tends to move in a straight line, and making use of Kepler's Third Law as to the relation between the time of a planet's revolution and its distance from the sun, Newton set forth his law of the inverse square, in accord with which the motions of the planets might be explained on the supposition that the sun produces an acceleration toward itself proportional to the inverse square of the distance of the planet from the sun: i. e. at twice the distance the acceleration is one fourth as great, and at four times the distance one sixteenth as great.

Newton found both a proof and a further application of this law in the revolution of the moon about the earth. Next he devised or elaborated the conception of Mass, and identified the weight of a body with the force exerted on it by the earth. He reached the combined conclusion that the earth attracts any body with a force inversely proportional to the square of the distance from the centre of the earth and directly proportional to the mass of the body. Conversely this attraction or gravitation is reciprocal; and the finally generalized statement of the law will be every material body attracts every other material body with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.23

Such was Newton's final rationalization, or ascription to a general law, of the movements of the earth and all the heavenly bodies. As for the cause or reason of this law of gravitation he had no hypothesis. Thus far had the system of Copernicus been brought within a century and a half. It did indeed represent a change from the mental and spiritual attitude, and symbolic and scholastic conceptions, of a Hugo of St. Victor, an Aquinas or a Dante. In these the human spirit, religiously inclined, had beautifully worked. But the intellect, the sheer mind

23 See Berry, Hist. of Astronomy, p. 228. Berry says that Newton formulated no such complete and general statement, but gave its parts in separate passages of the Principia.

of man, had never displayed itself as brilliantly as in that exposition of celestial physics which began, or rather, did not begin, with Copernicus, and was proved and perfected through the genius of Kepler, of Galileo and Newton, and the supporting labors of other mathematicians and astronomers. Within the compass of this theory or proven fact, the mind of pigmy man was calculating the courses of the stars in the unfathomable abysses of the universe.

CHAPTER XXXIV

THE NEW PHILOSOPHERS

I. TELESIO, CAMPANELLA, BRUNO

II. FRANCIS BACON

I

BESIDES anatomists and physiologists, physicists and astronomers, there were philosophers in the sixteenth century who vied with the scientists in their intellectual independence, and, as philosophers, surpassed them in the reach and looseness of their thought. The Aristotelians and Platonists have been spoken of. As followers of ancient systems they should not be classed with men whose thinking reflected the new thoughts of the time, scientific or otherwise. The latter were philosophers of nature, of the natural universe, terrestrial and celestial. Telesio (1509-1588), Bruno (1548-1600), Campanella (15681639), and Francis Bacon (1560-1626), greatest name of all, may be taken as their representatives. While their broad and independent and suggestive thinking held much of the past, it was impelled by the spirit of the time. With reservations as to Francis Bacon, their systems presented a certain magnificent confusion, and lacked a sure foundation in some irrefragible basic principle.

For they had broken with the authority of Aristotle, and had abjured the moulding power of logic and systematization which lay in the Aristotelian scholasticism. They were drawn in divers ways by thoughts from the antique, of Plato, or "Pythagoras," of Democritus and Lucretius, not to mention the Cabala. Thus confusedly equipped, they were at sea with their own thinking upon the metaphysics of the universe. Rather than sheer eclecticism, their opinions present a certain synthetic

originality. The wind-blown thinking of Telesio, of Bruno, of Campanella was to offer little guidance to future men. Its basic weakness lay in the lack of some fundamental principle of validity and certitude, such as Descartes was to discover in his cognito ergo sum.

It was not merely their metaphysics that were at sea. Their thoughts in general sprang from their imaginations pricked by the new physical theories and enlarging knowledge of the world. Their conclusions were not constructed painfully through inferences from the data of experience. Very different were the ways of these philosophers from the method of Vesalius, of Harvey, or of Galileo. Vesalius followed the teaching of his dissections; Harvey, likewise holding fast to his dissections of human bodies and his vivisections of animals, finally demonstrated his standardizing fact of the circulation of the blood; and what a Titan grasp had Galileo on the laws of motion, for example, which he had proved from his experiments. The sciences of physiology and of physics. terrestrial and astronomical could never be shaken from these basic principles which served to test the validity of all new inductions. Our philosophers had no such tests of natural truth; and Bacon, interested in all the phenomena of nature, records in his encyclopaedia all sorts of untested notions and statements, many of them unsound and some of them absurd. We may find that he was not a serious man of science according to the standards of Harvey or Galileo or William Gilbert's De Magnete, which Bacon held to be rather small beer.

We proceed then to these philosophers of a new view of the world, which was untested by anything within their knowledge or their reasoning.

Telesio's polemic against Aristotle shows what originality lay in his philosophy, which Bacon, his admirer, said was better at pulling down. He attacked the Aristotelian conceptions of matter and form as two separables, arguing that they were strictly in and of each other. Form was but the result of any natural process. He would substitute the principle of force indwelling in all matter, impelling and vivifying it. His force was heat,