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CARNEGIE INSTITUTION OF WASHINGTON. 



in the spectra to be compared, and for this purpose it has not been 

 found possible to depend on existing catalogues. The spectra have 

 all been classified from our own photographs made for radial-velocity 

 determinations. 



The results of about 20 photographs of this kind taken during the 

 year leave no doubt of a difference in the violet portion of the spectrum 

 between near and distant stars; 14 of the spectra show the distant star 

 to be much fainter in the violet region, while in the case of the other 6, 

 of which 2 are of the A type, there is little or no difference. In no case 

 is the nearer star relatively weak in the violet region. 



In order to supplement these results with a larger amount of material, 

 the radial-velocity photographs of the parallax stars and of the small 

 proper-motion stars have also been used. Although these w^ere taken 

 at a great variety of zenith distances and on different nights, it seems 

 probable that in forming two groups of results for considerable numbers 

 of small and large proper-motion stars the errors from these sources 

 should be very nearly the same in the two cases, and so not affect the 

 comparison. The spectra of all of the stars used in this way were 

 compared with a series of standard spectra at a number of points in 

 the violet and in the red portions of the spectrum, estimations being 

 made of their relative intensities. The standard spectra were then 

 measured under a Hartmann micro-photometer and the results for all 

 of the stars were reduced to densities. The values follow: 



It is evident, from these results, that while the nearer stars are much 

 stronger in the violet part of the spectrum than the more distant stars, 

 the amount of this effect depends upon the spectral type, being twice 

 as great for stars of types K0-K4 as for stars F0-F9. Since the average 

 proper motions for the groups of small and large proper-motion stars 

 are closely the same for the different types, we are obliged to conclude 

 that the difference in the intensity of the violet part of the spectrum 

 must be due largely to physical conditions in the stars themselves, the 

 atmospheres of the stars of great intrinsic brightness absorbing and 

 scattering the violet light more than those of the fainter stars. 



