NEW MEASUREMENTS OF DISTANCE OF SUN. 

 Relation between solar [larallax and eonstaui of ahcrrat'ion. 



117 



And suppose that by that time we are prepared to say quite defi- 

 nitely that the g-eonietrical vahie is not 8-77 seconds but 8 '80 seconds. 

 The most obvious sohition of the difficulty would be to conclude that 

 ihe simple theory of al)erration is not true, and to hand over the 

 j)roblem to the mathematical physicists, who might in the result find 

 that a definite geometrical determination of the solar parallax had 

 provided just the criterion wdiich they required to settle certain vexed 

 questions in dynamics. 



Again, should further investigation confirm the conclusion that 

 8 "76 seconds is the only value of the solar parallax wdiich wnll 

 reconcile the existing theory of the motion of the planet Avith the 

 observed value of the constant of gravitation, it may be that the con- 

 tradiction between the direct and the indirect methods will at last 

 enable the dynamical astronomers to lay a finger upon that flaw 

 which exists somewhere or other in the theory and makes it ini])ossi- 

 ble to say at the present time that all the motions of the solar system 

 can be completely explained. 



I have ventured to point out that the determination of the solar 

 parallax is a problem of wide interest, since it throws upon so many 

 dilferent people the task of keeping up their particular end against an 

 attack wdiose accuracy is gradually becoming more and more deadly. 

 The dimensions of the earth, as obtained by geodetic operations, are 

 necessarily beyond the reach of any criticism derived from solar 

 parallax results. 



Equatorial radius of earth. 



Miles. 



Mecbaiii and Delainbre. 1799 .'], 9f;i -T-l 



Airy, 1830 3, 9(i2 -82 



Everest 1830 3, 9l>2 -07 



Bessel. 1841 3, 9G2 -70 



Clarke, 18.58 3, 9(53 -31 



Clarke, 18GG 3, 9(53 -28 



Clarke, 1878 3, 9G3 -37 



Clarke, 1880 3, 9G3 -29 



Extreme rauge of these deteriuinatious Is only IJ in 4,000. 



