. THE HISTORY OF A STAR. 7 i 



Smash, a meteorite, collect the dust, expose it to a low tempera- 

 ture ; compare its spectrum with the spectrum of such, a body as 

 those we have been considering, and see by actual experiment if 

 there is any similarity. This was done. 



The result was almost identical. It seemed, therefore, that one 

 had at last got to solid ground, and could go ahead. But how to 

 go ahead in a scientific way ? Naturally by developing the argu- 

 ment which had led us so far. Let us agree that the nebulae are 

 condensations of meteoritic dust, and see whether we are led to 

 the true or the false by such a concession. Let us further grant 

 that the condensations go on. What will happen next ? 



In certain regions of space the encounters the collisions will 

 increase in number in consequence of the accumulation of me- 

 teoric dust in these regions ; the temperature will, therefore, be 

 higher and the light more intense. 



Is there only one process by which, the temperature can be in- 

 creased ? It did not take very long to recognize that there might 

 possibly be three lines of action, each one of which would result 

 in the production of a higher temperature. In the first place, 

 moment of momentum rotation being at our disposal to start 

 with, it was obvious, in virtue of mechanical laws, that as the con- 

 densation went on the rotation would be accelerated ; the motions 

 of the particles of dust in the reaction, so to speak, would be more 

 violent; the collisions, therefore, would produce more smashes, 

 and more heat, and therefore more light. 



We should get a central system and surroundings, such as Mr. 

 Roberts has recently photographed in the great nebula of An- 

 dromeda. The exposure he gave was four hours, and again this 

 photograph brings us face to face with phenomena which will 

 probably never be seen by the eye alone. 



A central condensation, here and there fragments of spirals, 

 and here and there dark gaps, are seen. These gaps were observed 

 by Bond and others years ago, but it remained for Mr. Roberts to 

 demonstrate to us that they are produced by the wonderful in- 

 draught action which we can now, by means of the photograph, 

 see going on. We have a concentration toward the center, the 

 dark gaps representing to us either the absence of matter or the 

 presence of meteoritic dust in a region where it is all going the 

 same way, and in which, therefore, there are no collisions. Here 

 and there we get regions of great luminosity, and associated with 

 the spirals we get obvious loci of encounters. External swarms 

 are also seen which have been thought, with great probability, 

 to belong to the system smaller condensations partaking in the 

 general motion of the whole. Here, then, we are in presence of 

 one possible cause of increased temperature. 



There is another. One of the early results obtained by Sir 



