MAGNITUDES AND DISTANCES OF STAE8. 24:7 



lately been shown, the almost invisible star 61 Cygni has a 

 greater parallax than a Cygni, though, according to an es- 

 timate based on Sir W. Ilerschel's assumption, it should be 

 about twelve times more distant — if, as it turns out, there 

 exist telescopic stars which are nearer to us than Sirius ; oi 

 what worth is the conclusion that the nebulae are very re 

 mote, because their component luminous masses are made 

 visible only by high telescopic powers ? Clearly, if the 

 most brilliant star in the heavens and a star that cannot be 

 seen by the naked eye, prove to be. equidistant, relative 

 distances cannot be in the least inferred from relative visi- 

 bilities. And if so, nebulae may be comp/iratively near, 

 though the starlets of which they are made up appear ex- 

 tremely minute. 



On the other hand, what.follow^s if the truth of tht^ as- 

 sumption be granted ? The arguments used to justify tnis 

 assumption in the case of the stars, equally justify it in the 

 case of the nebulae. It cannot be contended that, on the 

 average, the apparent sizes of the stars indicate their dis- 

 tances, without its being admitted that, on the average, the 

 apparent sizes of the nebulae indicate their distances — that, 

 generally speaking, the larger are the nearer, and the 

 smaller are the more distant. Mark, now, the necessary 

 inference respecting their resolvability. The lai-gest or 

 nearest nebulae will be most easily resolved into stars ; the 

 successively smaller will be successively more difficult of 

 resolution ; and the irresolvable ones wnll be the smallest 

 ones. This, however, is exactly the reverse of the fact. 

 The largest nebulae are either wholly irresolvable, or but 

 partially resolvable under the highest telescopic powers ; 

 while a great proportion of quite small nebulae, are easily 

 resolved by far less powerful telescopes. Kn instrument 

 through which the great nebula in Andromeda, two and a 

 half degrees long and one degree broad, appears merely &» 

 a diffused light, decomposes a nebula of fifteen minutes di- 



