310 POPULAR SCIENCE MONTHLY. 



as the one to be accepted until further investigation shall prove its 

 unsoundness. 



The second limitation has been the possible structure of an infinite 

 universe. The mathematical reader will easily see that the conclusion 

 that an infinite universe of stars would fill the heavens with a blaze of 

 light, rests upon the hypothesis that every region of space of some 

 great but finite extent is, on the average, occupied by at least one star. 

 In other words, the hypothesis is that if we divide the total number of 

 the stars by the number of cubic miles of space, we shall have a finite 

 quotient. But an infinite universe can be imagined which does not 

 fill this condition. Such will be the case with one constructed on the 

 celebrated hypothesis of Lambert, propounded in the latter part of 

 the last century. This author was an eminent mathematician, who 

 seems to have been nearly unique in combining the mathematical and 

 the speculative sides of astronomy. He assumed a universe constructed 

 on an extension of the plan of the Solar System. The smallest system 

 of bodies is composed of a planet with its satellites. We see a number 

 of such systems, designated as the Terrestrial, the Martian (Mars and 

 its satellites), the Jovian (Jupiter and its satellites), etc., all revolving 

 round the Sun, and thus forming one greater system, the Solar System. 

 Lambert extended the idea by supposing that a number of solar 

 systems, each formed of a star with its revolving planets and satellites, 

 were grouped into a yet greater system. A number of such groups form 

 the great system which we call the galaxy, and which comprises all the 

 stars we can see with the telescope. The more distant clusters may 

 be other galaxies. All these systems again may revolve around some 

 distant center, and so on to an indefinite extent. Such a universe, how 

 far so ever it might extend, would fill the heavens with a blaze of 

 light, and the more distant galaxies might remain forever invisible to 

 us. But modern developments show that there is no scientific basis 

 for this conception, attractive though it is by its grandeur. 



So far as our present light goes, we must conclude that although 

 we are unable to set absolute bounds to the universe, yet the great mass 

 of stars is included within a limited space of whose extent we have 

 as yet no evidence. Outside of this space there may be scattered stars 

 or invisible systems. But if these systems exist, they are distinct from 

 our own. 



The second question, that of the arrangement of the stars in space, 

 is one on which it is equally difficult to propound a definite general con- 

 clusion. So far, we have only a large mass of faint indications, based 

 on researches which cannot be satisfactorily completed until great ad- 

 ditions are made to our fund of knowledge. 



A century ago Sir William Herschel reached the conclusion that 

 our universe was composed of a comparatively thin but widely ex- 



