252 A Short History of Astronomy [CH. x. 



getting hold of all the unsold copies and in destroying 

 them, but fortunately he was also stimulated to prepare 

 for publication an authentic edition. The Historia Coelestis 

 Britannica, as he called the book, contained an immense 

 series of observations made both before and during his 

 career at Greenwich, but the most important and per- 

 manently valuable part was a catalogue of the places of 

 nearly 3,000 stars.* 



Flamsteed himself only lived just long enough to finish 

 the second of the three volumes ; the third was edited 

 by his assistants Abraham Sharp (1651-1742) and Joseph 

 Crosthwait ; and the whole was published in 1725. Four 

 years later still appeared his valuable Star-Atlas, which 

 long remained in common use. 



The catalogue was not only three times as extensive as 

 Tycho's, which it virtually succeeded, but was also very 

 much more accurate. It has been estimated t that, whereas 

 Tycho's determinations of the positions of the stars were 

 on the average about i' in error, the corresponding errors 

 in Flamsteed's case were about ID". This quantity is the 

 apparent diameter of a shilling seen from a distance of 

 about 500 yards ; so that if two marks were made at 

 opposite points on the edge of the coin, and it were placed 

 at a distance of 500 yards, the two marks might be taken 

 to represent the true direction of an average star and its 

 direction as given in Flamsteed's catalogue. In some 

 cases of course the error might be much greater and in 

 others considerably less. 



Flamsteed contributed to astronomy no ideas of first-rate 

 importance ; he had not the ingenuity of Picard and of 

 Roemer in devising instrumental improvements, and he 

 took little interest in the theoretical work of Newton ; 

 but by unflagging industry and scrupulous care he succeeded 

 in bequeathing to his successors an immense treasure of 



* The apparent number is 2,935, Dut 12 of these are duplicates. 



f By Bessel (chapter xin., 277). 



j The relation between the work of Flamsteed and that of Newton 

 was expressed with more correctness than good taste by the two 

 astronomers themselves, in the course of some quarrel about the 

 lunar theory : "Sir Isaac worked with the ore I had dug." " If he 

 dug the ore, I made the gold ring." 



