other leading men of the time. Thus, in Hooke's apprehension, the raison d'être of an hypothesis was not so much to suggest a physical connection of facts as to provide a convenient classification of experiments, and its most essential quality that it should be plausible, not that it should be true.
His judgment was besides warped, even more than that of most men, by that intellectual egotism which, if it sometimes acts as a spur to progress, more often performs the office of a drag. His self-love blinded him to the real merits of his competitors. His own speculations loomed so large before him as to exclude from his field of view those of every other. Newton acknowledged that, if he saw farther than most men, it was "by standing on the shoulders of giants." Hooke thought his own mental stature sufficient to entitle him to reject such extraneous aids. He accordingly set aside without hesitation Newton's discovery, offering his criticisms, not indeed discourteously, but with a certain air of superiority which not a little galled his sensitive antagonist. Matters were aggravated three years later when Newton published his beautiful explanation, on the emission hypothesis, of the colors of thin plates. Hooke declared that "the main of it was contained in the 'Micrographia,'" a remark extremely offensive to Newton, who, however, with his usual careful justice, immediately extended his somewhat scanty acknowledgment of his rival's labors, by defining with scrupulous accuracy the measure in which he was indebted to him. That Hooke was not devoid of generous sentiments appears from a letter which he wrote about this time to Newton, proposing a private correspondence on philosophical subjects. In it he acknowledges the superior abilities of the great mathematician, professes a dislike to contention, and hints that their relations had been embittered by the machinations of ill-disposed persons. (Oldenburg is evidently indicated.) Newton's reply was conceived in a corresponding spirit; but the harmony thus established was unhappily not lasting.
The problem of gravity was the supreme question of that time. It stood first among the orders of the day of the scientific council. It was instinctively felt that, until it should be disposed of, no real progress could be made in physical knowledge. And, slowly but surely, the way was being prepared for a great discovery. Galileo had made Newton possible. Men's ideas were gradually clarifying; the great cosmical analogies, now so familiar, were step by step emerging out of the dusk of ignorance; antiquated prepossessions were sinking, in a sediment of cloudy cavil, out of sight. Heaven was assimilated to earth, and earth to heaven; the old gratuitous separation between the starry firmament over our heads and the solid globe under our feet was abolished by acclamation, and it was felt that the coming law, to be valid, must embrace in its operation the whole of the visible uni-
- Brewster, "Life of Newton," vol. i., p. 138.