358 THE PRINCIPLES OF SCIENCE. 



brought into the solar system by the attractive powers of 

 Jupiter, Uranus, or other planets s. The classification of 

 nebulae as commenced by the two Herschels, and con- 

 tinued by Lord Eosse, Mr. Huggins, and others, will 

 probably lead at some future time to the discovery of 

 important empirical laws concerning the constitution of 

 the universe. The minute examination and classification 

 of meteorites, as carried on by Mr. Sorby and others, 

 seems likely to afford us an insight into the constitution 

 of the material universe. 



We should never fail to remember and record the 

 slightest and most apparently inexplicable coincidences or 

 correlations, for they may prove of importance in the future. 

 Discoveries begin when we are least expecting them. 

 It is a very significant fact that the greater number 

 of variable stars are of a reddish colour. Not all variable 

 stars are red, nor all red stars variable, but considering 

 that only a small fraction of the observed stars are known 

 to be variable, and only a small fraction are red, the 

 number which fall into both classes is too great to be 

 accidental h . It is also remarkable that the greater number 

 of stars possessing great proper motion are double stars, 

 the star 61 Cygni being especially noticeable in this 

 respect 1 . The correlation in these cases is not perfect 

 and without exception, but the preponderance is so great 

 as to point to some natural correlation, the exact nature 

 of which must be a matter for future investigation. Sir 

 John Herschel has remarked that the two double stars 

 6 1 Cygni and a Centauri of which the orbits were well 

 ascertained, evidently belonged to the same family or 

 genus k . 



g ' Philosophical Magazine,' 4th Series, vol. xxxix. p. 396 ; vol. xl. 



p. 183 ; vol. xli. p. 44. h Humboldt, 'Cosmos,' (Bohn) vol. iii. p. 224. 

 i Baily, ' British Association Catalogue,' p. 48. 

 k ' Outlines of Astronomy,' 850, 4th edit. p. 578. 



