( 301 ) 



for h' ciifFerent values (c = 15000 about) ^), we can calculate iov 

 each of Ihem the brightness and colour of the light, as well as the 

 temperature 2\ We then find for the degrees of glowing -{-1,0 

 and —1 



6'= 4- 1 69200 R + 68100 G + 175800 B 



1000 R + 1000 ö.-f 1000 B 



— 1 17,7 E + 15,7 G ,+ 6,3 B 



If we represent the colour contained in a total quantity of light 

 of 1000 by the quantities R, G, B and the brightness by magnitudes, 

 we shall find for 



h' — -\-l Col. = 221 i^ -[- 218 Ö + 562 i? Br. = -f 4,6 Mg. 



// = — 1 Col. = 445 R + 39Q G -i- 160 B Br. = — 4,4 Mg. 



Thus the first colour may be described as a mixture of 654 white 

 and 347 of a blue consisting of 3 R and 344 B, hence corresponding 

 in tint to ;. 466; the second colour is a mixture of 480 white and 

 521 of a yellow consisting of 285 R and 236 G, hence corresponding 

 to the wavelength / 587. A degree of glowing b' =^ — 2, corre- 

 sponding in colour almost with the light of petroleum, involves a 

 decrease in brightness of 8,6 magnitudes. 



For the calculation of the atmospheric absorption we have assumed 

 that the general absorption in a gas is inversely proportional to 

 the fourth power of the wavelength. For a layer of gas adopted 

 arbitrarily, which after a comparison with MtJLLER's spectral-photo- 

 metric measurements appeared to correspond to 1,05 atmosphere, 

 we have calculated ƒ(/) and thence found for the remaming quantity 

 of light, the initial quantity beijig 1000 R -f 1000 G + 1000 B : 



783 R-\- 771 Ö + 571^, 

 or reduced to 1000 as the sum, 



368 72 4- 363 G f 269^; 



the brightness is then 0,783 of the original brightness or is diminished 

 by 0,27 magn. 



The colouring due to the absorption by 1.05 atmospheres is almost 

 equal to that brought about by a diminishing of the degree of glowing 

 of '/,. For the latter yields 



257 72 + 248 + 184 5 

 hence when reduced to a sum of 1000 



372 72 + 3610+267 5 



i; In the paper read at Dusseldorf (see note p. 29-2) wrong temperatures are 

 given because the difference between b and b' was overlooked. The temperatures 

 16000^ 750G^ 5000 \ 3750\ 3000' G do not differ inter se 1, but only 0.43. 

 in degree of glowing. 



