G. W. Oolles, Jr.— Distance of the Stars. 265 



All these difficulties, however, may in time be eliminated. 

 A sufficient number of stars to calculate from is, in fact, a 

 matter only of time. These stars may then be selected with 

 regard to uniform distribution, and any drifts seen in certain 

 parts of the sky (if such are large enough to be worth considera- 

 tion) be allowed for in the equations. Professor Yogel's new 

 spectrographic method* promises accuracy amply sufficient, if, 

 as he claims, the probable error of the measurements is less 

 than one mile per second. We might even go so far, in our 

 speculative fancy, as to classify the stars according to their 

 spectra, and find the average distance of each class from our 

 system ; thus throwing some light on its real distribution in 

 the universe, and on our position with respect to the various 

 cl asses. f 



Table of 95 Stars used in the Calculation. 



The stars are arranged in order of right ascension. The 

 total proper motion of a star across the line of sight is given 

 by the formula a = vV + (15/>) 2 sin 2 D, in which v and p are the 

 motions in N". P. D. and R. A. respectively, and D is the N. 

 P. D. That is, a is considered the hypotenuse of a rectilinear 

 right triangle of which v and 15/) sin D (in seconds of arc) are 

 the sides. 



In the sixth column, the + and — signs denote recession 

 and approach of the star, respectively. The letters G, H, S 

 andY represent Greenwich Observatory, Huggins, Seabroke 

 and Yogel respectively (two or more for the same star repre- 

 senting a mean of different observers) ; but Y-S denotes Yogel's 

 mean of his own and Schemer's measurements given in his 

 "List of 51 Stars" {Monthly Notices, June, 1892). 



A few stars whose K. P. D. is slightly greater than 90° have 

 been inserted, by which discrepancy however the accuracy of 

 the result is not sensibly affected. The quantities in parenthe- 

 sis were not given in the sources referred to. 



M(/3) tt 



direction to all the stars considered, does not affect the ratio ;== — ; for if the 



M(a) 2 



stars had no other motion, this ratio would remain the same. The motion of the 



sun in its way may, indeed, be thus found by Doppler's principle. 



*See Monthly Notices R. A. Soc, December, 1891. 



f It is curious to note that Mr. Monck has already discovered that " solar stars 

 of any magnitude will, on the average, have a greater proper motion than the 

 Sirian ". (Messenger, Nov., 1891) — a statement strongly confirmed by Mr. J. E. 

 Gore's list (Astronomy and Astrophysics, Jan. 1892), in which 26 of the 29 

 greatest proper motion stars whose spectra have been observed are shown to be of 

 the solar class. This may, of course, be suggestive of their relative distance. 



