OUR PLACE IN SPACE 359 



Simon Newcomb. His idea in brief was this : within a radius 

 of 400,000 times the distance of the sun from the earth there 

 seems to be but one sun outside our own, the alpha Centauri 

 noted above. If the stars were sown with some evenness in 

 space, it would follow that the number of stars within a shell 

 of twice this radius would be the cube of this number that is 

 to say, eight. In a shell three times this unit of diameter there 

 would be twenty-seven, and so on, the number increasing always 

 with the cube of the diameter. The data at present available 

 for such a calculation are as yet meagre enough; neverthe- 

 less, in a way, the number observed agrees surprisingly with 

 the number calculated. Moreover, it is possible to check the 

 figures, in a way, from the measures of the proper motion of 

 the stars. It is obvious that on the average the stars nearest 

 to us will show the greatest annual change of position, and this 

 gives a second but very crude method of calculating their 

 number and distance. 



Putting these results together, Newcomb comes to the con- 

 clusion that five hundred such concentric shells would include 

 all of the stars visible to us by telescopic or photographic means. 

 This would give, on the supposition of a perfectly even dis- 

 tribution, something like 125,000,000 suns. It would mean a 

 stellar universe thirty-three hundred light-years from one 

 boundary to the other. But even conceiving that result is too 

 small, merely doubling this diameter would give a total of 

 eight times as many stars that is to say, 1000 millions in all. 

 The number is vast, but there is little or nothing to make it 

 improbable. We may go further yet ; we may take the out- 

 side limit set by I'Hermite that is to say, 66,000 millions. This, 

 on the same theory of even distribution, would require a universe 

 five to six thousand times the space to the nearest sun let us 

 say, roundly, a universe with a diameter of around 25,000 light- 

 years. 



Picture it, see it, realise it, who can ! 



It might seem as if we had here reached out far beyond the 

 powers of the telescope, and yet this is in no wise certain. 

 It was the calculation of Herschel that his twenty-foot reflector 

 would penetrate that is, reveal the existence of a star nine 

 hundred times the distance of Sirius, and that his forty-foot 

 reflector would penetrate twenty-eight hundred times the dis- 



