(142 ) 



Against the evidence of the q^ only one objection can be made, 

 namely that these classes K and M might have a proper motion 

 in common with the sun, so that q would not be a good measure 

 for the distance. A priori this objection is improbable but it may be 

 tested by material, which, though otherwise of small value, may for 

 this kind of investigations yield very valuable conclusions on this 

 point, namely the directly measured parallaxes. Hertzsprung gives 

 mean values of the measured parallaxes reduced to magnitude 0,0; 

 by the side of these we have given the values for somewhat different 

 groups derived from our .'T4.0': 



Derived from q jtq.o 



XIII— XIV .33 

 XV .14 



XVI— XX .096 



In general Hertzsprung's numbers are somewhat larger, this can 

 be easily explained by the circumstance that many parallaxes measured 

 in consequence of their large proper motions will probably be above 

 the mean. It appears sufficiently clear from this, at any rate, that 

 also the directly measured parallaxes markedly point at an increase 

 of brightness past class XIV, and that there is not the least ground 

 to assume for the other groups a motion in common with the sun. 



It is therefore beyond doubt that the K and M stars have a 

 greater intrinsic brilliancy than the F and G stars. Monck derives 

 from this fact that they have a greater radiating power, because 

 about the same value for the masses is derived from the double stars. 



That the latter cannot be derived from the double stars will 

 appear hereafter. Moreover Monck's conclusion of the greater radiating 

 power of the K and M stars is unacceptable. In incandescent bodies 

 this radiating power depends on the temperature of the radiating 

 layers and of the atmospheric absorptions. With unimpaired radiance 

 a greater amount of radiation is accompanied with bluer light (because 

 the maximum of radiation is displaced towards the smaller wave- 

 lengths) as both are caused by the higher temperature. The general 

 absorption by an atmosphere is also largest for the smaller wave- 

 lengths, so that when after absorption the percentage of the remain- 



