46
moon ’s movements, could have enabled him to compelthe scientific world to hearken to his reasoning, andto accept his conclusions. We can scarcely doubt thathe himself would never have attacked the subject ashe actually did, with the whole force of his stupendousintellect, had he not recognized in the moon’s move-ments the means of at once testing and demonstratingthe law of the universe. Had the evidence been onewhit less striking, the attention of his contemporarieswould soon have been diverted from his theories,which indeed could barely have risen above the levelof speculations but for the lunar motions. Astronomywould never have attained its present position hadthis happened. It would have seemed vain to trackthe moon and the planets with continually increasingcare, if there had been no prospect of explaining thepeculiarities of motion exhibited by these bodies.Kepler had already done all that could be done torepresent the planetary motions by empirical laws,—the planetary perturbations could be explained in nosuch manner. The application of mathematical calcu-lations to the subject would have been simply useless;and there would have been nothing to suggest theinvention of new modes of mathematical research, andtherefore nothing to lead to those masterpieces ofanalysis by which Laplace and Lagrange, Euler andClairaut , Adams, Airy, and Leverrier , have elucidatedthe motions of the heavenly bodies.
The history of the progress of investigation bywhich Newton established the law of gravitation is