72 



which must be considered before any final con- 

 clusions can be drawn regarding scattering in space 

 or its bearing on the extent of the universe. On 

 the other hand, the study of a problem w r hich 

 might seem to have little to do with the question 

 of stellar evolution has brought to light a physical 

 phenomenon which may prove to be an important 

 factor in the explanation of stellar development. 

 The first application of these results has provided 

 a new means of determining stellar distances. 



A NEW MEASURE OF STELLAR DISTANCES. 



We have already spoken of the apparent mag- 

 nitudes of the stars. Their absolute magnitudes, 

 on the other hand, are the magnitudes they would 

 have if they w r ere all at the same standard distance 

 from the earth. To calculate these, we must know 

 the distances of the stars. Conversely, if we can 

 obtain the absolute magnitude of a star in some 

 other way, we can determine its distance by com- 

 paring this with its apparent magnitude. 



A knowledge of the peculiarities of certain lines 

 in the sun's spectrum, derived from the solar in- 

 vestigations referred to above, suggested that their 

 relative intensities be determined in the spectra 

 of a list of stars of known absolute magnitude. 

 This brought out a surprisingly close correspond- 

 ence between these relative intensities and the 

 absolute magnitudes. Hence, by determining the 

 ratio of these intensities and the apparent magni- 

 tude for anv star of this class, w r e can at once 



