NEBULA NO MORE REMOTE THAN STARS. 249 



ne'julse, and globular and other clusters of all degrees of resoha^ 

 bility, and smaller scattered stars of every Inferior magnitude, 

 from the tenth to such as by their magnitude and minuteness con- 

 stitute irresolvable nebulosity, extending over tracts of many 

 square degrees. Were there but one such object, it might be 

 maintained without utter improbability that its apparent spheri- 

 city is only an effect of foreshortening, and that in reality a much 

 greater proportional difference of distance between its nearer and 

 more remote parts exists: But such an adjustment, improbable 

 enough in one case, must be rejected as too much so for fair argu- 

 ment in two. It must, therefore, be taken as a demonstrated fact, 

 that stars of the seventh or eighth magnitude, and irresolvable 

 nebula, may co-exist within limits of distance not differing in pro- 

 portion more than as nine to ten." — " Outlines of Astronomy," 

 pp. 614, 615. 



Now, we think this supplies a reduetio ad absurdum 

 of the doctrine we are combating. It gives us the choice 

 of two incredibilities. If we are to believe that one of 

 these nebulae is so remote that its hundred thousand stars 

 look like a milky spot, invisible to the naked eye ; we must 

 also believe that there are single stars so enormous that 

 though removed to this same distance they remain visible. 

 If we accept the other alternative, and say that many neb- 

 ulse are no further off than our own stars of the eifrhtb 

 magnitude ; then it is requisite to say that at a distance not 

 greater than that at which a single star is still faintly visi- 

 ble to the naked eye, there may exist a group of a hundred 

 thousand stars which is invisible to the naked eye. Neither 

 of these positions can be entertained. What, then, is the 

 conclusion that remains? This, only: — that the nebulae 

 are not further off from us than parts of our own sidereal 

 system, of which they must be considered members ; and 

 that when they are resolvable into discrete masses, these 

 masses cannot be considered as stars in anything like the 

 Drdinary sense of that word. 



And now, having seen the untenability of this idea, 

 11* 



