Tlie Xebular Hi/pothe^m: Its Present Condition. 177 



material from without, as well as of causing the enormous evohitiou of 

 heat of which I have spoken ; but there are one or two misconceptions 

 w^hich must be cleared away before the mind is prepared to admit the 

 possibility of such a circumstance. These misconceptions have 

 I'cference, firstly, to the distance of the nebulae from our own 

 system, and hence to their true volume ; and secondly, to the magni- 

 tude, or i-ather the mass, of the generality of comets. As regards the 

 former, it has clearly arisen from the unfortunate association of the 

 true gaseous nebulse with clusters of stars. Of the enormous distances 

 of the latter from us there can be no doubt ; but now that an entirely 

 different class of objects has been proved to exist m the heavens, 

 similar only in appearance to the most remote clusters, there can be 

 no reason to suppose that these are at the like distances. Indeed, it 

 would seem more probable that they are actually nearer to us, at lea.st 

 in some instances, than the nearest fixed stars themselves, for the 

 enormous magnitude which must be attributed to such a mass as the 

 great nebula in Orion, if it be supposed to be at a. very much greater 

 distance, must act as a bar to such an assumption. Indeed, the mind 

 experiences a sense of relief in believing that the nebulae are our 

 nearest neighbors, and the unif )rmity of nature, which does not offer 

 to our contemjjlation masses of matter incomparably greater than tho.se 

 we have to deal with in the solar system, seems to require that the 

 nebulse should not be conceived as of such surpa.ssing magnitude. If 

 this be admitted, it brings these objects almost within the range of 

 comets visiting the solar system ; but there are, doubtless, in the 

 heavens numerous groups or congeries of comets similar to these, not 

 to speak of those wonders which move in parabolic or hyperbolic orbits, 

 and which only require infinite time to travel infinite distance. Thus 

 the wide gulfs separating star from star, and which appear only to 

 exist to allow of the free revolution of stellar systems, may be the 

 theater not only of the movement of comets, but also of the evolution 

 of new world.s. 



The belief in the insignificant mass of most comets, which is also, I 

 think, open to question, is grounded on more substantial reasons. One 

 comet (Encke's) has actually been weighed against the smallest of our 

 planets. Mercury, and has kicked the beam, but perhaps no more 

 unfortunate instance for the experiment could have been selected than 

 this. It is a comet without stellar nucleus, and one that has made so 

 many revolutions round the sun, that supposing, as we have reason for 

 doing, it loses some portion of its matter at each visit, it must clearly 

 have been very much wasted at the time (1842) when Encke made its 

 perturbations by the planet Mercury the subject of his able researches. 



