230 GENERAL MOVEMENT OF THE STARS. 



contested by Masdler. He observes, however, that the recent re- 

 searches of Johnson and Otto Struve on the parallax of 61 Cygnus, 

 which raise its value to about one-half second, reduce the annual 

 proper movement of the Sun, if this last result be admitted, to about 

 8| radii of the earth's orbit, or 276 millions of leagues of 25 to the 

 degree; and he remarks that this velocity is ver} r nearly that of the 

 planet Mercury in the orbit it describes round the Sun. 



Let us again assume for the moment, with M. Masdler, the value 

 of the Sun's annual movement to be 12,295, as obtained above; 

 this movement, as it would be seen from the Pleiades, would be 

 expressed, according to the estimate before given of the arc CQ, by 

 the formula, 12,295 X sin 111°.5; which reduces the movement to 

 11.44. 



We have, then, for the parallax n of the group of the Pleiades, 

 assuming the estimate on a former page of its mean movement and 

 angle <p — <p\ 



0°.0582 rtn nnrnn 

 * = ■ = 0°.00509. 



The distance to the Sun corresponding to this parallax is about 4(H 

 million times the radius of the earth's orbit, a distance which it would 

 require about 640 years for the light to traverse. The two last num- 

 bers would be still greater if we assume the values relative to 

 Alcyone. 



The author shows that from the proper movement of our Sun, and 

 its distance from the central point, may be deduced, by means of 

 Kepler's third law, the proportion of the whole attractive mass which 

 revolves around Alcyone as a centre, to the mass of our Sun. 

 According to the preceding numbers, that whole mass would be about 

 one hundred and eleven million times that of the Sun. 



M. Msedler considers our solar system to be situated in a region of 

 the heavens comparatively very destitute of stars, but the regions of 

 mean stellar abundance to rate much lower in point of mass than the 

 space occupied by our planetary worlds. In this latter system, the 

 central mass exerts over the subordinate bodies, which are in limited 

 number, so considerable a force that the perturbations are there for 

 the most part of little importance. In the general stellar system an 

 analogous result is obtained in a different manner, namely, by the 

 immense number of the members of that system, obviating in this 

 respect the necessity for any preponderant central mass. 



The regions of the heavens near the group of the Pleiades, north 

 and south, are comparatively quite destitute of stars, especially from 

 /? of Perseus to ^ of Taurus. Farther away from the constellation, 

 there is again, in every direction, but chiefly towards the east, a great 

 abundance. Still farther on, we presently meet towards the west 

 another deficiency, along the zone which traverses Pisces and Pe- 

 gasus; while more to the east there occurs first the remarkable group 

 of the Hyades, and then a great diminution in the number of stars. 

 In other regions of the heavens we may observe that the richest in 

 stars have not the form of rounded groups, but rather that of 

 elongated zones, almost parallel to the Milky Way, and that between 

 these there are seen others destitute of stars. The southern heaveDS 



