34 COBLENTZ: COMPARISON OF STELLAR RADIOMETERS 



blue stars have about two times as much radiation as the yellow 

 stars, and about three times as much radiation as the red stars, 

 in the spectral region to which the eye is sensitive. 



A stellar thermocouple and a bolometer were compared and 

 the former was found to be the more sensitive. The conclusion 

 arrived at is that, from the appearance of the data at hand, 

 greater unprovements are to be expected in stellar thermocouples 

 than in stellar bolometers. 



The object of the investigation was to obtain some estimate of 

 the sensitivity required in order to be able to observe spectral 

 energy curves of stars. The radiation sensitivity of the present 

 apparatus was such that, when combined with a 3-foot reflecting 

 telescope, a deflection of 1 mm. would have resulted when ex- 

 posed to a candle placed at a distance of 53 miles. In order, 

 however, to do much successful work on stellar spectral energy 

 curves, a sensitivity one hundred times this value is desirable. 

 In other words, assuming that the rays are not absorbed in pass- 

 ing through the intervening space, the radiometric equipment 

 (radiometer aijd mirror) must be sufficiently sensitive to detect 

 the radiation from a candle removed to a distance of five hundred 

 miles. This can be accomplished by using a 7-foot mirror and 

 by increasing the sensitivity of the present radiometer (thermo- 

 couple and galvanometer) twenty times. This increase in sen- 

 sitivity is possible. 



Measurements were made to determine the amount of stellar 

 radiation falling upon 1 cm- of the earth's surface. It was 

 found that the quantity is so small that it would require the 

 radiations from Polaris falling upon 1 cm^ to be absorbed and 

 conserved continuously for a period of one million years in order 

 to raise the temperature of 1 gram of water 1°G. If the total 

 radiation from all the stars falling upon 1 cm- were thus col- 

 lected and conserved it would require from 100 to 200 years to 

 raise the temperature of 1 gram of water 1°C. In marked con- 

 trast with this value, the solar rays can produce the same effect 

 in about one minute. 



