92 Britain's Heritage of Science 



structure of the Universe. He looked upon the assemblage 

 of stars as an organic whole, and endeavoured to find 

 regularities in their distribution or arrangement. He thus 

 opened out an entirely new branch of enquiry. 



If stars were scattered at random, we should find on 

 the average an equal number in all parts of the sky. In 

 order to avoid the enormous and practically impossible 

 labour of actually counting the total number of stars 

 visible in his telescope, Herschel devised a method of 

 gauging the heavens, which gave him sufficiently good 

 average results. This consists in taking specimens, by 

 counting the stars which appear in a number of single fields 

 of view near together, and taking the average number of 

 stars recorded as an index of the density in this particular 

 region of the heavens. It is obvious that the number of 

 stars is vastly greater in the Milky Way than anywhere 

 else, and the question arose whether that dense conglo- 

 meration had any relation to the rest of the stellar universe. 

 It was, therefore, a discovery of the greatest interest and 

 importance to find that the stars throughout the heavens 

 increase in density as we approach the region of the Milky 

 Way, thus demonstrating that the visible universe is not an 

 accidental jumble, but possesses an organized structure. 



Results, of equal interest, were obtained from the close 

 investigations on double stars, of which about forty were 

 known when Herschel began his work. Having added 

 nearly 400 to this number, he set out to measure the relative 

 positions of the two components of each doublet, and, 

 repeating the measurements from time to time, discovered, 

 after twenty years of work, that some of these double stars 

 are physically connected, consisting of two huge and 

 luminous masses which revolve round each other. 



The organic bond which connects the separate units of 

 the universe revealed itself in a striking manner, by Halley's 

 discovery already referred to, that many of the stars are 

 apparently moving through space with considerable velo- 

 cities. Examining the direction and magnitude of the 

 observed shifts, Herschel noticed that if the average motion 

 be taken in any one region, that average is nearly the 

 same in different parts of the sky. As our observations 



