THE HISTORY OF A STAR. 67 



and to say that not only have we the same matter everywhere, 

 but all celestial bodies, including the earth, are due to an exqui- 

 sitely simple evolution of matter in the form of meteoritic dust. 

 We have no longer to rest content with the fact that all nature is 

 one chemically : we have the cause. 



Secondly, I propose to make as short and simple a statement 

 as I can of the general idea of the new cosmogony suggested by 

 the spectroscopic survey to which I have referred. 



I must, in the first place, ask my readers to grant me the scien- 

 tific use of their imagination ; and in order that it may not be 

 called upon to cope with questions as to whether space is infinite 

 or not, or whether space and time ever had a beginning, we will 

 not consider the possibility of the beginning of things or attempt 

 to define the totality of space, but we will in imagination clear a 

 certain part of space and then set certain possibilities at work. 



How much space shall we clear ? A very good idea of one of 

 the units of space which is very convenient for me to employ here 

 I mean the distance of the nearest star or one of the nearest 

 stars can be obtained by stating the time taken by light in per- 

 forming the journey between the earth and the stars, knowing as 

 we do that light travels one hundred and eighty-six thousand 

 miles in a second, In the case of the nearest stars the time thus 

 required is about three and a half years. With regard to the 

 twelfth-magnitude stars, we find that in all probability the dis- 

 tance in their case is so great that light, instead of taking three 

 and a half years, takes three thousand five hundred years to 

 reach us. 



The space included in a sphere with this radius will be suffi- 

 cient for our purpose. The stars that we shall have to abolish 

 for the purpose of this preliminary inquiry number something 

 like six millions ; the probability being that, if we consider the 

 stars visible, not in the largest telescopes, but in those which are 

 now considered of moderate dimensions, their numbers may be 

 reckoned at something between thirty and fifty millions. 



Imagine, then, this part of space cleared of all matter. We 

 shall have a dark void, and the probability is that all that dark 

 void will sooner or later, in consequence of conditions existing in 

 other parts of space into which we have not inquired, be filled 

 with some form of matter so fine that it is impossible to give it a 

 chemical name. 



Next we may imagine that this something without a chemical 

 name may curdle into something which is more allied with our ter- 

 restrial chemistry, and the chances are, so far as we know, that that 

 first substance will be either hydrogen itself or some substance 

 seen in the spectrum of hydrogen or closely associated spectra. 



It is just possible that at this point we enter the region of 



