394 THE STELLAR UNIVERSE. 



or rather sextuple star in Orion, and the star n, in the constellation called 

 Robur Caroli, as examples of nebulous appearances not easily explicable by 

 the supposition of distant masses of stars. " The nebulous character of these 

 objects," says he, " at least of the former, is very different from what might 

 be supposed to arise from the congregation of an immense collection of small 

 stars. It is formed of little flocky masses, like wisps of cloud; and such 

 wisps seem to adhere to many small stars at its outskirts, and especially to 

 one considerable star (represented, in the figure, below the nebula), which it 

 envelopes with a nebulous atmosphere of considerable extent and singular 

 figure. Several astronomers, on comparing this nebula with the figures of it 

 handed down to us by its discoverer, Huygens, have concluded that its form has 

 undergone a perceptible change. But when it is considered how difficult it 

 is to represent such an object duly, and how entirely its appearance will dif- 

 fer, even in the same telescope, according to the clearness of the air, or other 

 temporary causes, we shall readily admit that we have no evidence of change 

 that can be relied on." 



The impression of the necessity of admitting the existence of a subtle, 

 self-luminous, nebulous fluid in the universe, gradually stole upon the mind 

 of Sir William Herschel, and appears to be admitted by him with that re- 

 luctance which is felt when we are forced to admit something which a favor- 

 ite hypothesis fails to explain. 



¥* When I pursued these researches," says he, " I was in the situation of a 

 natural philosopher who follows the various species of animals and insects from 

 the height of their perfection down to the lowest ebb of life ; when arriving | 

 at the vegetable kingdom, he can scarcely point out the precise boundary 

 where the animal ceases and the plant begins, and may even go so far as to 

 suspect them not to be essentially different. But recollecting himself, he 

 compares, for instance, one of the human species with a tree, and all doubt 

 upon the subject vanishes before him. In the same manner we pass by 

 gentle steps from a coarse cluster down through others more remote, and 

 therefore of finer texture, without any hesitation, till we find ourselves brought 

 to an object such as the nebula in Orion, when we are still inclined to remain 

 in our once adopted idea of stars exceedingly remote and inconceivably crowd- 

 ed, as being the occasion of that remarkable occurrence. It seems, therefore, 

 to require a more dissimilar object to bring us right again. A glance like 

 that of the naturalist, who casts his eye from the perfect vegetable to the per- 

 fect animal, is wanting to remove the veil from the mind of astronomers." 



We must then conclude that appearances have been observed in the 

 heavens which can not be satisfactorily explained by the supposition of dis- 

 tant masses of stars. The supposition of self-luminous nebulous matter, dif- 

 fused in certain regions of the universe, has consequently been proposed as 

 the only other mode of explaining them. That such matter, if it exist, is in 

 the state or condition of vapor or fluid, is difficult to admit, since there ap- 

 pears more permanency about the nebular phenomena than could be easily 

 reconciled with such a state. The most eminent mathematician and natural 

 philosopher of the present century, has however adopted the supposition of 

 a widely-diffused nebulosity, and has made it the basis of one of the boldest 

 and most remarkable conjectures of modern times. Laplace has suggested 

 that systems such as that of our sun and planets, might be conceived to be 

 produced by the mere operation of mechanical laws out of such a nebular 

 chaos ! The gradual changes which this supposition compels us to admit 

 ) must be imagined to be so slow, that in the whole duration of our experience 

 or observation of the heavens they have not been perceptible. In other 

 words, the period of time over which astronomical observation extends, is 



