change has arisen mainly from including a larger number of stars, whose motions were determined with greater accuracy.
Former investigators based their conclusions entirely on stars having considerable proper motions, these being, in general, the nearer to us. The fact is, however, that it is better to include stars having a small proper motion, because the advantage of their great number more than counterbalances the disadvantage of their distance.
The conclusions reached by some recent investigators of the position of the solar apex will now be given. We call A the right ascension of the apex; D its declination.
Prof. Lewis Boss, from 273 stars of large proper motion found
A = 283°.3; D = 44°.l.
If he excluded the motions of 26 stars which exceeded 40" per century the result was
A = 288°.7; D = 51°.5.
A comparison of these numbers shows how much the result depends on the special stars selected. By leaving out 26 stars the apex is changed by 5° in R. A., and 7° in declination.
It is to be remarked that the stars used by Boss are all contained in a belt four degrees wide, extending from 1° to 5° north of the equator.
Dr. Oscar Stumpe, of Berlin, made a list of 996 stars having proper motions between 16" and 128" per century. He divided them into three groups, the first including those between 16" and 32"; the second between 32" and 64"; the third between 64" and 128". The number of stars in each group and the position of the apex derived from them are as follows:
Gr. I, 551 stars; A = 287°.4; D = x45°.0
II, 339 282°.2 43°.5
III, 106 280°.2 33°.5
Porter, of Cincinnati, made a determination from a yet larger list of stars with results of the same general character.
These determinations have the advantage that the stars are scattered over the entire heavens, the southern as well as the northern ones. The difference of more than 10° between the position derived from stars with the largest proper motions, and from the other stars, is remarkable.
The present writer, in a determination of the precessional motion, incidentally determined the solar motion from 2,527 stars contained in Bradley's Catalogue which had small proper motions, and from about 600 more having larger proper motions. Of the latter the declinations only were used. The results were:
From small motions: A = 274°.2; D = x31°.2
From large motions: 276°.9 31°.4
