90 LIGHT SCIENCE FOR LEISURE HOURS. 



pied 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 trav- 

 ersing 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 Yenus, was found an efficient 

 ally. 



The result of calculations founded on these methods 

 showed that the sun's distance, instead of being about 

 95,000,000 miles, is little more than 91,500,000 miles. 

 And recently, by a careful reexamination of the ob- 

 servations made upon Venus in 1769, Mr. Stone has 

 shown that they point to a similar result. 



Doubtless, however, we must wait for the transit of 

 Venus in 1874 before forming a final decision as to the 

 estimate of the sun's distance which is to take its place 

 in popular works on astronomy during the next cen- 

 tury or so. Nothing but an unlooked-for combination 

 of unfavorable circumstances can cause the failure of 

 our hopes. Certainly, if we should fail in obtaining 

 satisfactory results in 1874:, the world will not say that 

 the generosity of the English Government has been in 



