THE SUN'S MOTION IN SPACE. 175 



(70) Leo de Ball, 1877. — From the proper motions of 67 stars, 

 Leo de Ball found for the epoch 1860, the values 



R.A. = 269-°0 D.= +23°2 

 as denning the direction of the apex of the solar motion. 1 



(71) Preston, 1878.— In 1878, Tolver Preston raised the question 

 whether the motion of the sun in space is not due to the reaction 

 of the mechanical energy of the developed heat, this not being 

 produced uniformly throughout its surface. 2 



(72) Klinkerfues, 1878.— In 1878, Klinkerfues applied Bessel's 

 method of calculating and cartographically representing the poles 

 of the proper motion in considering the fixed-star system, and the 

 parallaxes and motions of its members. 3 He concluded that the 

 stars Vega, Capella, Sirius, and Fomalhaut have parallel motion 

 and belong to one system, or at least move as if they did ; a con- 

 clusion which Kobold points out loses its significance, if it be 

 remembered that the computed radiation-point of the convergence, 

 is very nearly identical with the antiapex of Madler's solar-motion, 

 adopted by Klinkerfues. The radiation point of the divergence was 



R,.A. = 272-°5, D.= + 32-°4 

 while Madler's direction, as before mentioned, was 

 R.A. = 261-°6, D.= +39-°9. 



(73) Maxwell-Hall, 1878. — Further data being now to hand in 

 regard to the parallaxes and radial velocities of about 23 stars, 

 their motions were investigated with reference to Maxwell-Hall's 

 hypothesis : the results on the whole appeared to confirm the 

 theory of the earlier paper. 4 



(74) Clerk-Maxwell, 1879.— In a letter to Mr. Todd of the 

 Washington N.A. Ofiice, dated 19th March, 1879, Clerk-Maxwell 

 remarked that if the sun be moving through the ether, the time 



1 Untersuchungen iiber die eigene Bewegung des Sonnensystems. — 

 Inaugural-dissertation, Bonn, 1877. 



2 A consideration regarding the proper motion of the sun in space. — 

 Phil. Mag., Vol. vi., Ser. 5, pp. 393-394, 1878. 



3 Ueber Fixstern-Systeme, Parallaxen und Bewegungen. — Veroffent- 

 lichen der k. Stern warte zu Gottingen, pp. 29 - 53, 1878. 



4 Monthly Not. Roy. Astr. Soc, Vol. xxxix., pp. 126-133, 1878. 



