86 Master Minds of Modern Science 



island of St Helena, where he spent a year and a half, 

 observing the stars of the Southern Hemisphere. In 1678 

 he had become a member of the Royal Society, and, young 

 as he still was, had had the honour to be chosen to lead 

 a discussion, the subject of which was whether more 

 accurate observations of the place of a star could be 

 obtained by the use of sights or by the use of a telescope. 

 This is good proof of the primitive state of telescopes in 

 the seventeenth century. 



It was Halley to whom we owe the publication of Sir 

 Isaac Newton's Principia, certainly the greatest scientific 

 work the world had yet seen, and it was Halley who took 

 such interest in the behaviour of the magnetic compass 

 that William III gave him a captain's commission in the 

 Navy, and placed him in command of a small vessel called 

 a ' pink/ so that he might study this subject. Study it 

 he did, making long voyages far into the Southern Seas, 

 as well as doing much work relative to the tides around 

 British coasts. He was a good friend to Flamsteed, and 

 at the latter 's death was chosen to succeed him. 



[Halley was then over sixty years of age, and he came 

 to an observatory where there were no instruments, for 

 Flamsteed's widow had removed all her husband's 

 property. Halley managed to get a grant from the 

 Government, however, and made a transit instrument 

 and a large quadrant, both of which still hang in the 

 Observatory. 



Halley's name is best remembered in connexion with 

 Halley's comet. This great comet passed flaming through 

 the solar system in the year 1682, and Halley, after com- 

 puting its path, began to make investigations with the 

 object of discovering whether this comet could have 

 visited our system at any previous epoch. He found that 

 it closely resembled in appearance and orbit a comet 

 which had appeared in 1607 and another seen in 1531 ; 

 he decided that this was the same comet, with an orbit of 



