138 INORGANIC EVOLUTION. [CHAP. 



We must also expect, if we are dealing with small particles of 

 meteoritic dust, .that the action will be very quick, and that the war 

 will be soon over. All this really agrees with the facts. In the case 

 of the new star we were fortunate enough to have the opportunity 

 of observing in the northern hemisphere, not very long ago, the new star 

 in the constellation Auriga, we obtained undoubted indications of the 



K H h G- F 



Fia. 42. The spectrum of Nova Aurigae, showing both bright and dark lines. 



fact that we were dealing with two different masses of matter ; for the 

 reason that if we take the chief spectral lines marked G, h, H and K 

 (Fig. 42), that is to say, the lines of hydrogen and of calcium, we find 

 both bright lines and dark lines, which being interpreted means that 

 hydrogen and calcium were both giving out light and stopping light. 

 We cannot imagine that the same particles of calcium and of hydrogen 

 were both giving out light and stopping light ; there must have been 

 some particles of hydrogen and calcium giving light and others stopping 

 light ; and if we look at the photograph carefully we find that the 

 bright lines and the dark lines are side by side, and we know that that 

 means a change of wave-length in consequence of movement, and we 

 also know from the change of wave-length indicated that the differential 

 velocity of the particles which gave us the bright hydrogen and calcium, 

 and the dark hydrogen and calcium, must have been something like 

 500 miles a second. In that way we obtained indisputable proof that 

 we were really dealing with two perfectly different series of particles 

 moving in opposite directions, and that that was the reason we got that 

 sudden illumination in the heavens which as suddenly died out until 

 finally a nebula previously undiscovered was found to occupy the place. 

 The nebula is really not the result, the nebula was the cause, but we 

 did not know of its existence until our special attention had been 

 drawn to that part of the heavens. 



B. In relation to Distance. 



So much, then, for the first statement of facts relating to the dis- 

 tribution of the various star groups and nebular groups in the most 

 general form. The next question is, can we say anything about the 

 distances of these bodies *? 



The way in which an astronomer attempts to determine the dif- 

 ferent distances of the various stars from the earth, may be very well 



