158 



REPORTS ON INVESTIGATIONS AND PROJECTS. 



The principal interest in the computing section of the Department at the 

 Dudley Observatory during the past year has been in the study of systematic 

 proper-motion, based upon our Preliminary Catalogue of 6,i88 stars, pub- 

 lished early in 1910. It was for purposes similar to this that the researches 

 upon proper-motion were originally undertaken by the Department of Me- 

 ridian Astrometry. 



This year has been fruitful in results. In a paper published in the Astro- 

 nomical Journal, Nos. 623-624, April 3, 191 1, it was found that when the 

 stars are divided into spectral types the mean motions of successive types 

 ascertained by their "cross-motions" — those at right angles to the meridians 

 of solar-motion and to the line of vision — with their ascertained relations to 

 the entire amount of motion in space, and assuming the velocity of the sun 

 in space to be 20 k. per second (in his later paper Professor Campbell finds 

 this velocity to be 19.5 k. per second), the mean half velocity of each type, 

 arranging in the supposed order of age, beginning with the supposedly 

 youngest, B, is as exhibited in the following table, in the last column of 

 which are quoted the corresponding half velocities ascertained from the mo- 

 tions in the line of sight (radial velocities) determined at the Lick Observa- 

 tory, or at the D. O. Mills station, near Santiago de Chile, upon stars of the 

 fifth magnitude or brighter. The results for types B and A found by Frost 

 agree with the corresponding values by Campbell. 



Table of mean half velocities of stars of various spectral types as ascertained from 

 a study of "cross motions" and of "radial motions." 



* Boss in Astronomical Journal, No. 624, p. 19S. 

 t Campbell in Lick Observatory Bulletin, No. 196. 



The accordance of the values of the mean half velocities of the proper- 

 motions of the stars of the several stellar types most certainly indicates that 

 there is a real acceleration with age if, as is commonly supposed, the types 

 are correctly arranged in the order of age — B the youngest and M the 

 oldest — considering only the stars of the foregoing list. 



At the same time, with the researches in regard to the type already pub- 

 lished and summarized in the preceding table, the general law of the veloci- 

 ties as to direction and of the relative velocity as to direction was carefully 

 investigated. The conclusion can be summarily stated as follows : The dis- 

 tribution in direction seems to be virtually at random, but the linear velocities 

 in the general direction of the constellation Orion (at approximately the 



