230 SCIENCE FROM AN EASY CHAIR 



great question whether the earth moves or not." At that 

 time the earth was " suspected " to move round the sun, 

 but no proof of that motion had been given. M. Auzout 

 did not succeed in his laudable attempt, simply because 

 Newton's great discovery of the law of gravitation had 

 not then been made. 



Edmund Halley was the intimate friend and passionate 

 admirer of Newton. He paid out of his own pocket for 

 the publication of Newton's Principia by the Royal 

 Society in 1686, the society having expended all its 

 available funds in printing a great work on Fishes (which 

 shows how at the first, as now, the society cared for the 

 whole range of the study of Nature). Halley was able 

 to show that comets move regularly round the sun, in 

 obedience to the same law of gravitation which controls 

 the movements of the planets and of our earth itself; so 

 that many of them are regular members of the solar 

 system. Halley especially calculated out the form of the 

 orbit of the comet of 1682 as an ellipse, and the time 

 of its journey and recurrence, or " period," as it is called, 

 which he showed to be about seventy-five or seventy-six 

 years. He predicted its recurrence in 1758. Halley died 

 in 1742, at the ripe age of eighty-six, having, amongst other 

 good deeds, founded the Royal Society Club, which still 

 dines every Thursday in the session. His comet reappeared 

 in 1759, a few months later than he had, owing to incom- 

 plete details used in his calculation, expected; but the 

 accuracy of his scheme of its movement was demonstrated. 

 It duly appeared again in 1835, and it is now awaited in 

 the spring of 1910. Halley himself had identified his comet 

 with that of 1607 and of 1531, and lately, by the aid of 

 records from an ancient seat of astronomical observation 

 actually from China it has been traced back to the 

 month of May in the year 240 B.C. It has caused con- 

 sternation and terror times enough since then, of some 



