205 



EXPLANATIONS. 



forms according to which we have arranged them, and whicll 



seem to indicate the steps of a stupendous progress. 



" 1. Astronomers have never rested their belief in the reality 

 and wide diffusion of the nebulous matter on the objects referred 

 to in the first paragraph, but on others much within the range of 

 our previous vision. In so far as we have hitherto understood the 

 nature of clusters', the telescopic power required to resolve them 

 is never very much higher than that which first descries them as 

 dim milky spots. But there are many most remarkable objects 

 which, in this essential feature, are wholly contrasted with clus- 

 ters. For instance, the nebula in Orion, as I have fully shown in 

 the text, is visible to the naked eye, as also is the gorgeous one in 

 Andromeda ; while the largest instrument heretofore turned to 

 them has given no intimation that their light is stellar, but rather 

 the contrary ; although small stars are found buried amidst their 

 mass. Now, if Lord Rosse's telescope resolves these, and others 

 with similar attributes, such as some of the streaks among the fol- 

 lowing plates, we shall thereby be informed that we have general- 

 ized too hastily from the character of known firmaments — that 

 schemes of stellar being exist, infinitely more strange and varied 

 than we had ventured to suppose; and certainly we shall then 

 hesitate in averring further concerning the existence, or at least 

 the diffusion of the purely nebulous modification of matter. 



" 1. Lord Rosse's telescope may also, as I have said, disprove 

 the reality of our arrangement of the forms of the nebulae as steps 

 of a progression. And in regard to this question, there seem two 

 classes of objects meriting attention. 



" First. 1 shall refer to the nebulous stars properlv so called, or 

 to that form in which the diffused matter has reached the condition 

 of almost pure fixed stars. Now, of these objects there are two 

 distinct sets, presenting at first to the telescope very much the 

 same appearance, but in regard of which our knowledge is very 

 different. It will readily be conceived that a distant cluster, with 

 strong concentration about the centre of its figure, must, to the 

 telescope which first descries it, look like a star with a halo around 

 it. When a higher power is applied, that central star, however, 

 will appear as a disk, and to a still higher power the cluster will 

 be revealed. A very great number of what are called nebulous 

 stars are doubtless of this class ; and we have hitherto had no 

 means of accurately ascertaining the fact, just because our largest 

 telescopes were required to descry them ; but there are multitudes 

 of others — the true ' photospheres '—quite of a different descrip- 

 tion. Many of these are easily seen as fixed stars with haloes of 

 different sizes diminishing to the mere 1 bur and under the great- 

 est power as yet applied, the apparent central star never expands 

 into a disk, or departs from the stellar character. It is by its effect 

 on these that the new instrument will at all bear on this portion ot 

 the nebular hypothesis. 



" Secondly. The foregoing being our grounds of belief in the 

 existence of nebulae — first, in a diffused or chaotic state, and again 

 in a condition proximate to pure stars ; the only remaining point 

 has reference to nebulae in an intermediate state — when the 

 roundish masses seem to have begun a process of organization or 

 concentration, and carried it onwards through several stages ; a 

 state to which we have every variety of analogon in the vanoeis 



