And to us it is enough that gravity does really exist, and act according to the laws which we have explained, and abundantly serves to account for all the motions of the celestial bodies and of our sea."(2) The very magnitude of the importance of the theory of universal gravitation made its general acceptance a matter of considerable time after the actual discovery.

This opposition had of course been foreseen by Newton, and, much as he dreaded controversy, he was prepared to face it and combat it to the bitter end.

He knew that his theory was right; it remained for him to convince the world of its truth.

He knew that some of his contemporary philosophers would accept it at once; others would at first doubt, question, and dispute, but finally accept; while still others would doubt and dispute until the end of their days.

This had been the history of other great discoveries; and this will probably be the history of most great discoveries for all time.