MOUNT WILSON OBSERVATORY. 233 



(5) The values of the solar motion derived from giant and from dwarf stars 

 differ radically. The former give a value of 18.8 km. and the latter 31.7 km. 

 The value of the solar motion is much larger if based upon stars of large pecu- 

 liar motion than upon those of small motion. 



A similar investigation of the space-motions of the A-type stars has been 

 begun by Stromberg. The parallaxes used are those derived by the spectro- 

 scopic method recently developed by Adams and Joy, and the radial velocities 

 are from the results obtained at several different observatories. The com- 

 ponents of space-velocity for 332 stars have been computed. 



The results of this investigation, so far as completed, are of especial interest 

 in proving that the first and second star-streams, which were found by Kap- 

 teyn to be especially well marked among the A-type stars, are identical with 

 the Taurus and the Ursa Major groups, respectively. In addition to these, 

 there is a central group of small systematic motion which is probably identical 

 with the antapex stream of Boss and Eddington and the O stream of Halm. 

 This central group contains a comparatively small number of A-type stars, 

 but probably nearly all the later-type giants, if we may judge from the agree- 

 ment of their systematic motions. Over one-half of all the A stars can be 

 regarded as members of the Ursa Major group. The stars recognized as 

 belonging to the Taurus group are found among the intrinsically fainter A 

 stars, a result similar to that which had previously been found to hold for those 

 of the F type. 



All of the groups appear to show an ellipsoidal distribution of velocities 

 along nearly parallel axes, and the amount of ellipticity is of the same order 

 as that of the F stars. 



Stellar Classification. 



The report of the Commission on Stellar Classification of the International 

 Astronomical Union, prepared by Messrs. Adams and Russell, was presented 

 by the latter at the meeting of the Union in Rome and was adopted without 

 substantial alteration. The report embodies numerous extensions and addi- 

 tions to the Harvard system of classification now in general use, which have 

 been made with a view to increasing the capacity of the system to describe 

 spectral phenomena. No radical change, however, is suggested in the existing 

 nomenclature. 



Classification of the Spectra of Faint Stars in Kapteyn's Selected Areas. 



The classification of the spectra of stars between the tenth and twelfth 

 photographic magnitudes in the Selected Areas has been commenced by Mr. 

 Humason with the 60-inch telescope. For this purpose he is using the large 

 slitless focal-plane spectrograph especially designed for the work and already 

 described. Satisfactory spectra have been obtained with this instrument on 

 a linear scale of approximately 6.3 mm. between H/3 and H5. The usable field 

 on each plate covers a region about 40' by 40' square. 



At least 10 stars between the eleventh and twelfth photographic magnitudes 

 will be photographed in each area. For most of the areas a single plate will 

 give this number, but in some cases two or three plates will be needed. With 

 an exposure time of 5 hours, well-exposed spectra of twelfth-magnitude stars 

 are obtained at the center of the field. H and K are seen and estimates of 

 type can be made within less than one-half of a spectral interval. In the 



