SEQUEL TO THE EPOCH OF NEWTON. 219 



Halley announced, in 169 1 8 , his intention of fol- 

 lowing this idea into practice ; in a paper in which 

 he corrected the text of three passages in Pliny, in 

 which this period is mentioned, and from which 

 it is sometimes called the Plinian period. In 1710, 

 in the preface to a new edition of Street's Caroline 

 Tables, he stated that he had already confirmed it 

 to a considerable extent 9 . And even after Newton's 

 theory had been applied, he still resolved to use 

 his cycle as a means of obtaining further accuracy. 

 On succeeding to the Observatory at Greenwich in 

 1720, he was further delayed by finding that the 

 instruments had belonged to Flamsteed, and were 

 removed by his executors. "And this," he says 10 , 

 " was the more grievous to me, on account of my 

 advanced age, being then in my sixty-fourth year ; 

 which put me past all hopes of ever living to see 

 a complete period of eighteen years' observation. 

 But, thanks to God, he has been pleased hitherto 

 (in 1731) to afford me sufficient health and strength 

 to execute my office, in all its parts, with my own 

 hands and eyes, without any assistance or inter- 

 ruption, during one whole period of the moon's 

 apogee, which period is performed in somewhat 

 less than nine years." He found the agreement 

 very remarkable, and conceived hopes of attaining 

 the great object, of finding the longitude with the 

 requisite degree of exactness ; nor did he give up 



8 Phil Trans, p. 536. Ib. 1731, p. 187- 



10 Ib. p. 193. 



