JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V JANUARY 19, 1915 No. 2 



ASTROPHYSICS. — A comparison of siellar radio7neters and 

 radiometric measurements on 110 stars.^ W. W. Coblentz, 

 Bureau of Standards. 



In this paper experiments are described showing that there is 

 but little difference in the radiation sensitivity of stellar thermo- 

 couples constructed of bismuth-platinum, and thermocouples 

 of bismuth-bismuth -f- tin alloy, which have a 50 per cent higher 

 thermoelectric power. Improvements in the method of main- 

 taining a vacuum by means of metallic calcium are described 

 whereby it will be possible to go to the remotest stations for mak- 

 ing radiation measurements without carrying an expensive 

 vacuum pump. With this outfit measurements were made on 

 the radiation from 112 celestial objects, including 105 stars. 

 This includes measurements on the bright and the dark bands 

 of Jupiter (also a pair of his satellites), the rings of Saturn, and a 

 planetary nebula. Quantitative measurements were made on 

 stars down to the 5.3 magnitude; and high grade qualitative 

 measurements were made on stars down to the 6.7 magnitude. 

 It was found that red stars emit from 2 to 3 times as much total 

 radiation as blue stars of the same photometric magnitude. 



Measurements were made on the transmission of the radiations 

 from stars and planets through an absorption cell of water. By 

 this means it was shown that, of the total radiation emitted, the 



' Detailed paper to appear in the Bulletin of the Bureau of Standards. 



33 



