720 



SCIENCE. 



[N. S. Vol. III. No. 73. 



of time. The star, therefore, has appar- 

 ently moved from the first to the second 

 position. But there are several things to be 

 taken into account before we can say how 

 much the star has moved. The effects of 

 precession and nutation and the aberration 

 of light must be eliminated. When this is 

 done it is found that only a very few stars 

 have an accurrately determined motion of 

 their own among their fellows. Schonfeld, 

 of Bonn, has published a list of 83 stars that 

 liave a proper motion in a year greater than 

 1 " of arc, i. e., greater than the angle sub- 

 tended by three-tenths of an inch to the ej-e 

 placed one mile away. Only 83 of all the 

 hosts of stars are known to move at right 

 angles to our line of sight 1 " of arc or 

 more in one year. 



The star which has the greatest proper 

 motion so far known is ISo. 1830 of Groom- 

 bridge's Catalogue. This star moves 7" of 

 arc in a year. The star is so far away that 

 this small apparent motion across our line 

 of sight means, if the distance has been ac- 

 curately determined, a very startling linear 

 velocity of more than 230 miles in a second, 

 a speed ' uncontrolable, according to New- 

 comb, by the combined attractive power of 

 the entire sidereal universe.' 



Groombridge 1 830 is not the only ' run- 

 away ' star in the list, there are several 

 others ; Gierke remarks " the fact then 

 confronts us that not a few of the stars pos- 

 sess velocities transcending the power of 

 government of the visible sidereal system. 

 Is that system threatened with dissolution, 

 or must we suppose the chief part of its at- 

 tractive energy to reside in bodies unseen, 

 because destitute of the facultj' of luminous 

 radiation? No answer is possible ; conjec- 

 ture is futile. We are onlj^ sure that what 

 we can feebly trace is but a part of a mighty 

 whole, and that on every side our imperfect 

 knowledge is compassed about by the 

 mystery of the Infinite." 



When we consider pro^^er motions less in 



amount than 1" a year the list swells in 

 number to over 3,000. The astronomer of 

 the XXth Century will be able to de- 

 termine the proper motions of thousands of 

 other stars, using the superb catalogues 

 constructed in this century. In studying 

 this problem the aid of the spectroscope 

 has been called in, and with that wonder- 

 ful instrument it has- been found possible 

 to measure the velocity of quite a number 

 of stars in the line of sight, either directly 

 from us or toward us. At Potsdam and at 

 Greenwich and elsewhere, by the use of 

 measurements or photographs of stellar 

 spectra or by visual observations, Aldeb- 

 aran, the brighest star in the constellation 

 of Taurus, has been found to be moving 

 from the earth at the rate of 30 miles a 

 second. The Greenwich observers tell us 

 that the North Star is moving toward us at 

 the rate of 16 miles a second. Vogel, at 

 Potsdam, places the motion of Arcturus at 

 45 miles a second from the earth. When 

 we combine the motion in the line of sight 

 with the motion at right angles to that line, 

 we can discover the real motion in space, 

 its amount and direction. At the Lick Ob- 

 servatory Mr. Campbell has proposed to de- 

 termine with the spectroscope in what 

 du'ection the solar system is moving among 

 the stars. 



The motion of our solar system among 

 the stars has interested astronomers for 

 many years. Sir Wm. Herschel first in- 

 vestigated this problem a century ago. The 

 fundamental principle of the investigation 

 is this : Those stars which lie in the direc- 

 tion in which we are going will appear to 

 open out from each other, while those in 

 the part of the skj^ that we are leaving will 

 close up behind us. Since Herschel's time 

 the materials for investigation have been 

 greatlj^ augmented. An examination of the 

 stellar proper motions has been made by 

 many calculators, and especially recently 

 by Prof Boss, of Albany, and by Mr. Oscar 



