Page:Popular Science Monthly Volume 59.djvu/499

Rh common to all matter? Was it identical with the attraction of the earth which caused bodies near it to fall toward its center? Were the revolutions of the planets and the revolution of the moon phenomena referable to one and the same great law of nature? The result which Newton had reached in his investigations in 1665 seemed to render this doubtful, or at least presented a difficulty for the time inexplicable. Accordingly, with that characteristic reticence to which we have previously referred, Newton refrained from communicating to any one the important discovery he had made, preferring to await the solution of the difficulty which the anomalous fact of the apparent intensity of the earth's attraction at the moon presented.

Three years afterwards, in June, 1682, Newton attended a meeting of the Royal Society. Whilst in London, he accidentally learned that Picard in France had just measured the arc of the meridian with great accuracy, and that the result which he obtained for the length of a degree in that latitude differed somewhat from the measurement previously accepted as reliable. Newton at once perceived the importance of this fact in connection with the determination of the intensity of the earth's attraction. If the commonly received measure of a degree of the meridian was erroneous, the accepted estimate of the size of the earth was erroneous; moreover, if the assumed semi-diameter of the earth was incorrect, the supposed distance of the moon from the earth, in the calculation of which the earth's semi-diameter is involved, must also be incorrect. The possible explanation of the annoying result he had reached in 1665 was immediately suggested. Obtaining accurately the measurement of a degree of the meridian as given by Picard, immediately on his return to Cambridge he determined the size of the earth and the distance of the moon, on the supposition that Picard's measurement was the true one. With the data thus obtained he returned to the problem at which he had labored sixteen years before, and by the same method then pursued sought anew to determine the law of the variation of the earth's attraction. Perceiving, as he advanced in the calculation, the tendency of the numbers to produce the desired result, he became so much agitated that he was unable to finish the computation and was under the necessity of requesting a friend to do it for him. The identity of the force which causes bodies near the earth to fall toward its center and that which causes the heavenly bodies to revolve was fully established, the universality of the law of gravitation was finally and forever demonstrated, the solution of the grand problem of the universe was complete.

We might have supposed that Newton would have eagerly hastened to announce his great discovery and secure for himself the eminent honor to which he was entitled, and yet more than two years elapsed before the discovery was published to the world; and then, not of his