Mar., 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



55 



We will then place the Sun at Greenwich Observatory. 

 We shall need a table 5 feet in diameter to represent the 

 whole of the solar system upon. We will divide space 

 up into concentric spheres, the Sun being at their common 

 centres. These space spheres will on our map be repre- 

 sented by circles. The first circle we will draw with a 



We' have 9 times the area of the first circle, but we must 

 recollect it represents a sphere of space, and is therefore 

 27 times the volume of the space sphere of 5 light-years 

 radius. 



We shall here be able to map, including the first 

 sphere, from the stars whose parallaxes are known, in 



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radius of 5 miles, to represent a space sphere of 5 light- 

 years radius ; but we shall, besides the Sun, have here 

 only one star to locate. This will be a Centauri, and 

 we must place it 4-34 miles from the Observatory — it 

 will come near Bromley. 



We will now draw another circle at 15 miles radius. 



the Northern Hemisphere 14 stars, I central star (the 

 Sun), and 6 stars in the South. But the Southern Hemi- 

 sphere is, so far, less completely surveyed than the 

 Northern, so that we may e.xpect to add, say, 6 stars to 

 the South, making a total of 27 stars. 



We have, therefore, a probable average of i star for 



