TEE LAW OF GRAVITATION. 489 



commou 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, Kewton 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 meet- 

 ing of the Eoyal 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. Kewton at once perceived the im- 

 portance 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 deter- 

 mined the size of the earth and the distance of the moon, on the sup- 

 position that Picard's measurement was the true one. With the data 

 thus obtained he returned to the problem at which he had labored six- 

 teen years before, and by the same method then pursued sought anew 

 to determine the law of the variation of the earth's attraction. Perceiv- 

 ing, 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 re- 

 questing 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 univer- 

 sality 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 



