The Milky Way 



spectrum, it is reasonable to infer that an 

 equal surface of each emits the same quantity 

 of light; consequently the amount of light 

 received from these two stars, when placed 

 at the same distance, must be proportional 

 to their surfaces; we are therefore able to cal- 

 culate the first and to measure the second. 

 We find in this manner that the diameter of 

 Sirius is approximately equal to eleven million 

 kilometres, about seven times the sun's diameter. 

 Thus, while we still lack the systematic measure- 

 ments demanded by Kapteyn, the distance 

 has been determined of numerous stars in all 

 parts of the heavens, from the most brilliant 

 down to stars of the sixth magnitude. Enough 

 is already known to enable us to assert that 

 while the average dimensions of the stars are 

 somewhat superior to those of the sun they are 

 nevertheless comparable. The sun is, how- 

 ever, a relatively small unit in the stellar world. 

 At the same time we come to the new notion 

 that the heavens are, on the average, homo- 

 geneous; the stars near to us are, in general, 

 neither larger nor smaller than the distant 



ones. This remark is of importance, because 



227 



