224 CARNEGIE INSTITUTION OF WASHINGTON. 



while the 60-mch has enabled Adams to measure the distance of many- 

 remote stars by his new and powerful spectroscopic method, and to 

 double the known extent (so far as spectroscopic evidence is con- 

 cerned) of Kapteyn's star-streams, a much greater advance into space 

 is necessary if we are to learn what community of motion obtains 

 among the stars comprising the galactic system. Recent experiments 

 encourage the hope that without inadmissible sacrifice of precision of 

 measurement, the Hooker telescope will enable us to determine the 

 radial velocities of stars of the eleventh magnitude, which are doubtless 

 truly representative of the Galaxy. 



In preparing an observational program to include such faint objects, 

 the process of selection employed must be very carefully considered, 

 in the hope of securing a maximum return within a reasonable period of 

 time. So far as possible, the stars in Kapteyn's Selected Areas should 

 evidently be given preference, because of the vast amount of work 

 completed or projected for the purpose of determining their positions, 

 proper-motions, and visual and photographic magnitudes. Con- 

 siderations such as spectral type, the known directions of star-stream- 

 ing, and the position of the chosen regions with reference to the plane 

 of the Galaxy, must also be given adequate weight, though the final 

 list should not rest too exclusively upon any hypothesis, but should 

 contain enough widely distributed material to permit of independent 

 statistical discussion. It is of fundamental importance that the 

 method of spectroscopic parallaxes will permit dwarf stars to be distin- 

 guished from giant stars rendered faint by their much greater distance. 



The stellar spectrograms obtained in this campaign will afford rich 

 material for the study of many questions other than stellar distribution 

 and star-streaming, such as the relationship between mass and speed, 

 the nature of giant and dwarf stars, and other capital problems. The 

 results obtained within a few years will serve as the basis for a fresh 

 orientation, and indicate in what way the initial program of observa- 

 tions can be most advantageously revised. 



Shapley's recent studies of globular clusters have indicated the signif- 

 icance of these objects in any general attack on evolutional or struc- 

 tural problems. The possibility of determining their parallax, by a 

 number of independent methods, is of prime importance, both in its 

 bearing on the structure of the universe and because it permits a host 

 of apparent magnitudes to be at once transformed into absolute 

 magnitudes. In the further development of this work, the Hooker 

 telescope should be chiefly employed, partly because of the gain in 

 light resulting from its large aperture, and also because of the increased 

 scale of crowded clusters at the 134-foot focus, where the spectra of 

 stars, commingled in the 60-inch, can be separately photographed. 

 With a spectrograph of small dispersion it has already been found 

 possible to photograph the spectra of fourteenth-magnitude stars in 



