138 PLEASANT WA YS IN SCIENCE. 



the hypothesis of uniform distribution and all the conclusions 

 founded on it 



Thirdly, and most obviously of all, the lucid stars ought 

 not to be associated in a marked manner with the figure of 

 the Milky Way. To take an illustrative instance. When 

 we look through a glass window at a distant landscape we do 

 not find that the specks in the substance of the glass seem 

 to follow the outline of valleys, hills, trees, or whatever 

 features the landscape may present. In like manner, regard- 

 ing the sphere of the lucid stars as in a sense the window 

 through which we view the Milky Way, we ought not to find 

 these stars, which are so near to us, associated with the 

 figure of the Milky Way, whose light comes from distances 

 so enormously exceeding those which separate us from the 

 lucid stars. Here again, then, if there should appear signs 

 of such association, we must abandon the theory that the 

 sidereal system is constituted as Sir Wm. Herschel supposed. 



It should further be remarked that the three arguments 

 derived from these relations are independent of each other. 

 They are not as three links of a chain, any one of which 

 being broken the chain is broken. They are as three strands 

 of a triple cord. If one strand holds, the cord holds. It 

 may be shown that all three are to be trusted. 



It is not to be expected, however, that the stars as 

 actually seen should exhibit these relations, since far the 

 larger number are but faintly visible ; so that the eye would 

 look in vain for the signs of law among them, even though 

 law may be there. What is necessary is that maps should 

 be constructed on a uniform and intelligible plan, and that 

 in these maps the faint stars should be made bright, and the 

 bright stars brighter. 



The maps exhibited during this discourse [since pub- 

 lished as my " Library Atlas "] have been devised for this 

 purpose amongst others. There are twelve of them, but 

 they overlap, so that in effect each covers a tenth part of 

 the heavens. There is first a north-polar map, then five 

 maps symmetrically placed around it ; again, there is a 



