SEQUEL TO THE EPOCH OF NEWTON. 215 



derived from the theory, and the comparison of 

 these with observation. The advancement of as- 

 tronomy would alone have been a sufficient motive 

 for this labour ; but there were other reasons which 

 urged it on with a stronger impulse. A perfect 

 lunar theory, if the theory could be perfected, 

 promised to supply a method of finding the lon- 

 gitude of any place on the earth's surface ; and 

 thus the verification of a theory which professed 

 to be complete in its foundations, was identified 

 with an object of immediate practical use to navi- 

 gators and geographers, and of vast acknowledged 

 value. A good method for the near discovery of 

 the longitude had been estimated by nations and 

 princes at large sums of money. The Dutch were 

 willing to tempt Galileo to this task by the offer 

 of a chain of gold : Philip the Third of Spain had 

 promised a reward for this object still earlier 1 ; the 

 parliament of England, in 1714, proposed a recom- 

 pense of 20,000/. sterling ; the Regent Duke of Or- 

 leans, two years afterwards, offered 100,000 francs 

 for the same purpose. These prizes, added to the 

 love of truth and of fame, kept this object con- 

 stantly before the eyes of mathematicians, during 

 the first half of the last century. 



If the tables could be so constructed as to re- 

 present the moon's real place in the heavens with 

 extreme precision, as it would be seen from a 

 1 Del. A.M.l 39, 66. 



