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THE POPULAR SCIENCE MONTHLY 



Table II 

 Transmission of Stellar Eadiaition Through a 1 cm. Layer of Water 



Object 



Remarks 



Blue Stars 



a Lyne.... 

 a Aquilse. 

 Orion is. 



58 I (Vega) 



69 (Altair) 



42 I (Rigel) A low value for a blue star 



Yellow Stars 



a Auriga.... 



a Bootis 



a Tauri 



7 Draconis. 



(Capella) 

 ( Arcturus) 

 ( Aldebaran) 



Red Stars 



/3 Pegasi [ 3Ih 



a. Orionis J/a 



a Scorpii j J/« p 



a Herculis 



Jupiter 



Venus . 

 Satur.i. 

 Moon.. 



(Betelgeux) 

 ( Antares) 



Receiver in center of disk including part 



of dark band. 

 Receiver covers upper dark band. 



Receiver covers central disk. 



water cell will be less for the red star, Class M, than for the yellow 

 star, Class F, G, K, and a blue star. Class B, A. This is the true condi- 

 tion of affairs, as may be noticed in Table II., which gives the per- 

 centage of the total energy falling upon the thermocouple, which is 

 transmitted by the water-cell, for blue, yellow and red stars. From this 

 table it may be seen that as much as 60 per cent, of all the radiations 

 coming from a blue star lies in the spectral region to which the eye is 

 sensitive, while only from 20 to 30 per cent, of the total radiation 

 received from a red star affects the eye and the photographic plate. 

 This brings out very clearly why it is that a red star of the same 

 visual brightness as a blue star (causes a larger galvanometer deflec- 

 tion) emits from two to three times as much total radiation. It means 

 that from 70 to 80 per cent, of the radiation from a red star lies in the 

 infra-red — beyond the spectral region to which our eyes are sensitive. 



The absorption cell tells us nothing of the size or the distance of the 

 star. It indicates that the shape of the spectral energy curve of the 

 star is such that only about one fourth of the, total energy emitted by a 

 red star lies in the visible and in the ultraviolet part of the spectrum. 

 However, it should dispel all doubt as to the quality of the radiations 

 emitted by red and by blue stars. The absorption does more than 

 merely tell us the region of the spectrum in which the most energy is 

 distributed. It may prove useful in detecting dark companions of 



