490 POPULAR SCIENCE MONTHLY. 



own motion but at the instance of his friend, Halley, wlio subsequently 

 boasted that he was the Ulysses who had discovered Achilles and 

 brought him forth from his concealment. In the month of August, 

 1684, Halley, having become satisfied that Hooke could not furnish the 

 demonstration of the law of gravitation which he had repeatedly 

 promised, visited Cambridge to confer with iS'ewton on the subject on 

 which he had become deeply interested and been long laboring without 

 any satisfactory result. He inquired of jSTewton, what would be the 

 curve described by the planets on the supposition that the attractive 

 influence of the sun diminished as the square of the distance ? Newton 

 at once replied, 'An ellipse.' When asked how he knew this, he re- 

 plied: 'I have calculated it.' Halley, surprised and delighted at the 

 announcement, asked to see the demonstration. Newton was unable to 

 lay his hands on the calculation he had made two years before, nor 

 could he at the moment reproduce it. He promised Halley however 

 that he would send him the demonstration as soon as he was able, and 

 in the month of November following he fulfilled his promise. Halley 

 immediately revisited Cambridge to obtain Newton's consent to the 

 publication of the discovery. In this he succeeded, and on the 10th of 

 December he informed the Royal Society of the discovery and that 

 Newton had consented to prepare a paper on the subject for the society. 

 In February, 1685, the promised cormnunication was received — a paper 

 of twenty-four pages, containing four theorems and seven problems. 

 He refers to it in the accompanying letter, as his 'Notions about 

 Motion.' This humble yet most memorable paper ever presented to 

 the Society was the germ of 'The Principia.' 



The great discovery having been made public, Newton seems to 

 have felt that the time had come to enter on the gigantic task he had 

 doubtless proposed to himself when the discovery was first made but 

 which other occupations had hitherto prevented him undertaking, 

 namely, putting his demonstration in a complete and conclusive form 

 and applying it to the solution of the many interesting and sublime 

 problems which the phenomena of the material universe presented. 

 For two years he dismissed from his mind all other occupation, and 

 devoted himself with all the energy of his mighty intellect to the 

 Herculean task. With untiring industry, prolonged attention, and 

 intense thought, probably never paralleled in the history of intel- 

 lectual effort, he lived but to meditate and calculate; oftentimes so 

 wholly absorbed with the grand themes which occupied his mind as to 

 be for the time unconscious of all the ordinary concerns of life. Fre- 

 quently, on rising in the morning he would sit for hours on his bedside 

 arrested by some new conception, and had it not been for the attention 

 of the members of his family would often have neglected to take his 

 daily food. 



