TIME, SPACE, AND INVISIBLE WORLDS. 



245 



go to show that just as our Sun controls dark Planets like Earth, 

 and bright Planets like Jupiter, so Astronomers reasoning from 

 analogy and continuity, assisted by telescopic scrutiny, have con- 

 cluded that the same conditions likewise obtain in the case of the 

 lucid Stars around us. The argument applies with concentrated 

 force to those red advanced stars like Alpha Herculis and Mu 

 Cephei, the greatest portion of whose Planets in all probability 

 have died down to darkness and solidity long ago. 



If further proof were needed, several instances might be named 

 of short variable stars like Algol, where the darker Sun or Planet, 

 in the course of its close orbit, actually intervenes between us and 

 the primary, thus detracting from the latter's brilliancy, and giving 

 rise periodically to that change in brightness which we character- 

 ise as variability. 



The total number of Stars visible in largest telescopes has been 

 variously estimated from thirty millions upwards. Of these only 

 a very small fraction, about six thousand, are separately distinguish- 

 able by the naked eye, under favourable circumstances. Those 

 of first and second magnitudes are undoubtedly much larger than 

 our Sun, and, in some cases, as much larger as our Sun is than 

 Jupiter. How many are smaller, it is not possible to say ; but 

 being certain that a considerable number of the lower magni- 

 tudes, like some in the Pleiades, appear so, only by reason 

 of their enormous distance, we may not err, perhaps, if we 

 regard each of these six thousand as, on an average, equal in 

 bulk to our Sun. Let us also assign to each an average 

 of eight primary Planets, as in our System, thus giving a total 

 of 48,000 Planets, in addition to attendant Satellites, Com- 

 etary Systems, etc. Half of these 48,000 we will suppose to be 

 incandescent like Saturn, and the remaining 24,000 to be dark and 

 solid like Earth, Mars, Venus, and Mercury. Let us now divide 

 this number, as a tribute to the majority of Sirian or " young " 

 Stars, also to any faint Stars whose light may have become dim, 

 and whose heat dulled, through age ; and whose planets, therefore, 

 may have already passed the life-bearing stage ; and also as an 

 allowance for any planets which, owing to excess or deficiency of 

 heat and light, or other cause, have proved incompetent for the 

 development of life. We thus arrive at twelve thousand dark 



