VENUS ON THE SUN'S FACE. ?l 



The error was first detected when other modes of 

 determining the sun's distance were applied by the 

 skilful astronomers and physicists of our own day. We 

 have no space to describe as fully as they deserve the 

 ingenious processes by which the great problem has been 

 attacked without aid from Venus. Indeed, we can but 

 barely mention the principles on which those methods 

 depend. But to the reader who takes interest in astro- 

 nomy, we can recommend no subject as better worth 

 studying than the masterly researches of Foucault, 

 Leverrier, and Hansen upon the problem of the sun's 

 distance. 



The problem has been attacked in four several 

 ways. First, the tremendous velocity of light has been 

 measured by an ingenious arrangement of revolving 

 mirrors; the result combined with the known time 

 occupied by light in travelling across the earth's orbit 

 immediately gives the sun's distance. Secondly, a 

 certain irregularity in the moon's motion, due to the 

 fact that she is most disturbed by the sun when 

 traversing that half of her path which is nearest to 

 him, was pressed into the service with similar results. 

 Thirdly, an irregularity in the earth's motion, due to 

 the fact that she circles around the common centre of 

 gravity of her own mass and the moon's, was made 

 a means of attacking the problem. Lastly, Mars, a 

 planet which, as we have already mentioned, approaches 

 us almost as nearly as Venus, was found an efficient 

 ally. 



The result of calculations founded on these methods 



