NO. 19 ENERGY SPECTRA OF STARS — ABBOT AND ALDRICH 7 



for each star. From these data factors were computed to reduce all 

 the mean deflections to what they would have been if observed outside 

 the atmosphere. 



One other correction was desired to allow for the effect of the 

 imperfect reflection of the numerous mirrors in the optical train. We 

 had intended to determine this by observing the solar spectrum with 

 the identical apparatus, and comparing with the known energy spec- 

 trum of the sun. But we were unsuccessful in this experiment on 

 the one afternoon when we could try it. Hence as a substitute we 

 estimated the transmission of the optical train as follows. In a future 

 expedition we intend to observe the solar spectrum very carefully. 



Including the telescope and spectroscope there were eight alumi- 

 nized mirrors in the train. We shall neglect selective absorption and 

 reflection in the two fused-quartz lenses and the prism, thinking that 

 the selective differences, while doubtless not negligible, would be 

 small in these parts within the wave-length range 4230 to 8170 A. 

 All the mirrors were recently aluminized and may be assumed to have 

 the following reflection characteristics : 



Table 4. — Factors for optical train 



Wave length 423 .448 .471 .505 -559 -622 .750 .817 



Reflection % 94 94 94 94 93 93 92 92 



Eighth power of % 61 .61 .61 .61 .56 .56 .51 .51 



Owing to the large percentage accidental error of the observations, 

 and our expectation of publishing greatly improved results next year, 

 we do not give here the results for individual stars. We divide the 

 eight stars in groups with regard to spectral class. Moreover, in 

 taking mean values within the groups, we reduce the stars to about 

 equal levels of brightness, by considering their respective magnitudes. 

 Applying these several reductions we arrive at table 5. 



Table 5. — Average energy distribution for spectral types, as of outside the 



atmosphere 



Energy values for given groups of stars and spectra 



