230 THE WORLD MACHINE 



it was this that enabled Newton and his successors to calculate 

 the figure of the earth. But of still greater importance were 

 the observations taken upon the position of Mars simultane- 

 ously with like observations of Cassini in Paris. The idea was 

 to utilise the transit of Mars instead of the moon for the deter- 

 mination of the sun's distance. 



It was the first attempt which had ever been made on such 

 broad lines that is to say, from such widely separated points 

 of the earth. It was with a fever of impatience that the French 

 Academy awaited the return of its deputies. The observations 

 were successfully carried out ; combining their results with his 

 own, Cassini was able to fix the parallax of the sun, not at three 

 minutes, such as the estimates of the ancients had required ; 

 not at one minute, which Kepler had thought probable, but at 

 slightly less than one-sixth of a minute. Cassini set it at nine 

 and a half seconds. 



This fixed the remoteness of the sun at three hundred and 

 sixty times the distance of the moon, or eighty-seven millions of 

 earthly miles. This was in 1673 that is, thirteen years before 

 the Principia, fifty years after the Dialogues on the Two Great 

 World Systems ; it was in the midst of the reign of the elegant 

 and easy-going voluptuary, Louis XV., which, like that of his 

 similar in England, the second Charles, proved so favourable to 

 the advancement of rational ideas. 



A century and more of minute and repeated observations, 

 checked and verified by methods most diverse, has not im- 

 peached the substantial accuracy of Cassini's results. It was 

 still a little under the reality. But before this prodigious cal- 

 culation how men must have stood in amaze ! There was now 

 no easy or contemptuous brushing it aside. France was then 

 the political, the social, the literary, the scientific centre of 

 Europe. The expedition to Cayenne had been sent out by the 

 king, under the direction of the Royal Academy. The calcula- 

 tions were the work of the Royal Astronomer, the official head 

 of scientific investigation in the most enlightened of the nations. 

 The results had in some sort a royal sanction ; they had, more- 

 over, been carried out with a care and precision hitherto 

 unknown ; to contest their value was to set one's face against 

 all that stood for truth and knowledge in that day. It was a 

 wonderful change ; a short fifty or sixty years since the Holy 

 Congregation of the Index, sitting at Rome, had denounced the 



