176 CARNEGIE INSTITUTION OF WASHINGTON. 



While there is considerable variation between the observed and 

 real probable errors of the different authorities, it may be said that 

 the observed probable errors represent the true probable errors fairly 

 accurately in a systematic sense. 



STELLAR LUMINOSITIES AND ABSOLUTE MAGNITUDES. 



Employing the systematic corrections to parallax previously alluded 

 to, the absolute luminosities and magnitudes of a large number of 

 stars were derived. Generally speaking, the results of Russell were 

 confirmed. For the stars of type K and M the division into "giant" 

 and "dwarf" stars is very marked, while the stars of types A and B 

 are practically wholly confined to the "giant" class. For F and G 

 type stars, however, there appears to be a considerable proportion of 

 stars intermediate between the two classes. Accidental errors in the 

 determination of magnitude or type could easily account for some of 

 the intermediate stars. There may also be a physical explanation. 

 If we admit the possibility of Russell's suggested development of a 

 star from M "giant" through intermediate types to M "dwarf," it is 

 very probable that many stars never develop beyond the F or G type, 

 and this would account for the intermediate class of absolute magni- 

 tudes among the F and G type stars. 



The absolute magnitudes of the "dwarf" stars present an almost 

 arithmetical progression from F to K type, but the M-type stars are a 

 full magnitude fainter than an arithmetical progression would indicate. 

 The range of absolute magnitude for the "giant" stars is considerable. 

 Taking means by type there is an increase in magnitude from "giant" 

 M-type to "giant" G and then a decrease. 



REAL STELLAR MOTIONS. 



The first attempt of the Director to discuss the real motions of the 

 stars was based upon fairly uniform material in a systematic sense. 

 The parallaxes, published by Adams and Joy, and the proper-motions 

 of the Preliminary General Catalogue were used exclusively. Radial 

 velocities were taken from the results published by the Lick and 

 Mount Wilson observatories. From this data the apices of the real 

 motion of each star were computed, together with the velocity in 

 space. The total number of stars discussed was 219. In spite of the 

 small number, several striking phenomena were quite definitely shown. 



1. There is a Solar Group, so termed because it is moving approxi- 

 mately in the direction of solar motion at a rate of about 22 kilometers 

 per second. The true coordinates of this motion are A = 270°, D = + 16°. 

 The group is mainly composed of "giant" stars. 



2. The solar motion determined from "dwarf" stars is in sufficient 

 agreement with that determined from "giant" stars to suggest the 

 conclusion that they belong to the same system. 



