SOLAR AND STELLAR PROPER MOTIONS. 
149 
Lande 6 infers the displacement of the solar system in the 
following terms:—“ Mais une force quel-conque imp rim ee a 
un corps, et capable de le faire tonrner autour de son centre, 
ne pent manquer aussi de deplacer le centre, et Ton ne sanroit 
concevoir Tun sans l’autre. II paroit done tres-vraisembla- 
ble qne le Soliel a un mouvement reel dans l’espace absolu,” 
etc. 
For more than sixty years the study of the hypothesis of 
solar or stellar motion had been devoted simply to testing 
the reality of the phenomena. The problem of the direc¬ 
tion and the magnitude of the translation still remained 
unsolved; in fact, its solution had not been seriously at¬ 
tempted. 
On March 6, 1783, William ITerschel 7 gave in detail be¬ 
fore the Royal Society his methods of attacking this problem. 
He used the most carefully determined proper motions of 
fourteen well known stars. From an examination of these 
motions he suspected that they indicated a translation of the 
Solar system toward the constellation of Hercules. Assum¬ 
ing the point to which this motion tended, to be near the Star x 
Herculis he found that more than eighty per cent of the proper 
motions, of these stars, in, right-ascension and in declination, 
were such as they would be if the assumed point were what 
he termed the true apex of the solar motion. Regarding the 
magnitude of the solar motion, he offered only the following 
hints:—“ From the annual parallax of the fixed stars, which, 
from my own observations, I find much less than it has 
hitherto been proved to be, we may certainly admit (with¬ 
out entering into a subject which I reserve for a future op¬ 
portunity) that the diameter of the earth’s orbit, at the dis¬ 
tance of Sirius or Arcturus, would not nearly subtend an 
angle of one second; but the apparent motion of Arcturus, 
if owing to a translation of the solar system amounts to no 
less than 2".7 a year, * * * Hence we may in a gen- 
6 La Lande, J. Histoire de l’Academie Royale des Sciences. Paris, 1776 ; 
518. 
7 Herschel, William. Philosophical Transactions, 1783 ; 247. 
