MIRACLES OF SCIENCE 



but unfortunately Mars, even at his nearest, is some- 

 thing like 50,000,000 miles distant, and his relatively 

 large size adds to the difficulty of focusing on his 

 centre with the degree of accuracy necessary for 

 this delicate measurement. Nevertheless the esti- 

 mates of the sun's parallax deduced from measure- 

 ment of the parallax of Mars are closely in accord 

 with other estimates and serve to confirm our knowl- 

 edge of the true scale of the planetary map. 



In point of fact the various estimates were so 

 concordant that the actual parallax of the sun was 

 known toward the close of the nineteenth century 

 with a degree of accuracy that would fairly satisfy 

 any one but an astronomer. Professor Moulton tells 

 us that in 1891 Harkness made a discussion of all 

 the material bearing on the subject and obtained as 

 a final value of the solar parallax 8.809 seconds with 

 a possible variation of .006 of a second; and that in 

 1896 Newton obtained from all available material 

 the number 8.797 seconds, with a possible plus or 

 minus variation of .007 of a second. To the layman 

 this may seem accurate enough; but the astronomer 

 is always eager to grasp new means of verifying 

 his measurements and calculations, and so there was 

 intense interest manifested in the (discovery, made 

 in 1898, of the little planetoid called Eros. [ 



The reason was this : Planetoids in general, it I 

 will be recalled, having orbits lying between Mars 

 and Jupiter. But it was soon noted that the orbit of 

 Eros is extremely eccentric, and the computation 

 showed that one part of its journey would bring it 

 within the orbit of Mars, and hence nearer to us than 



