SIDEREAL ASTRONOMY. 345 



making it barely possible to do so. Nearly a century ago an 

 old English astronomer, Mitchell, computed the chances as 

 more than half a million to one, that the stars of the Pleiades 

 could not have been thus arranged by accident', and the 

 computation has been sanctioned by later authority. They 

 are a system in themselves, and in their concentration and 

 conceivable magnitude may possibly form a powerful centre 

 of attraction to worlds around them. 



While saying thus much of Madler's theory, from the 

 slight notice of it in the Cosmos, we are bound to add that 

 a serious objection exists in the fact that the Pleiades lie 26 

 out of the plane of the Milky Way ; and that it is scarcely 

 possible dynamically to suppose any general movement of 

 rotation out of the plane of this great stratum of our stellar 

 system. To settle the arduous question, whether a rotation 

 of the Gralaxy in its own plane exists or not, Sir ,T. Herschel 

 proposes the assiduous observation in right ascension and 

 polar distance of a certain number of stars in the Milky 

 Way, judiciously selected in both hemispheres, and including 

 all magnitudes down to the lowest distinctly observable ; and 

 he asserts his belief that a strict perseverance in such re- 

 search for thirty or forty years could not fail to settle the 

 question. It is an object well worthy of the labour thus 

 suggested.* 



The Chapter on the Nebulae has all the interest which 

 belongs to a masterly outline of the most wonderful depart- 

 ment of human research. All the numerical measures of 

 space and time with which we have hitherto been dealing, 

 dwindle into nothing when compared with those which the 

 nebulas place before us. Instead of numbering the stars 

 of a system, we are here numbering separate systems of stars. 

 The nebulas, whose places in the heavens have been exactly 

 determined, now surpass 3,600 ; exceedingly various in outline, 



* Outlines of Astronomy, p. 589. 



