g24 Dr. Herscehi/s Astronomical Observations 
which is now nebulous, is represented as perfectly out of all 
nebulosity, and can hardly be supposed to have been affected 
when Huyghens observed it. 
The changes that are thus proved to have already hap- 
pened, prepare us for those that may be expected hereafter 
to take place, by the gradual condensation of the nebulous 
matter ; for had we no where an instance of any alteration in 
the appearance of nebulae, they might be looked upon as per- 
manent celestial bodies, and the successive changes, to which 
by the action of an attracting principle they have been con- 
ceived to be subject, might be rejected as being unsupported 
b}' observation. 
The various appearances of this nebula are so instructive, 
that I shall apply them to the subject of the partial opacity of 
the nebulous matter, which has already been inferred from its 
planetary appearance, when extremely condensed in globular 
masses ; but which now may be supported by more direct 
arguments. For when I formerly saw three fictitious nebulous 
stars, it will not be contended that there were three small 
shining nebulosities, just in the three lines in which I saw them, 
of which two are now gone and only one remaining. As well 
might we ascribe the light surrounding a star, which is seen 
through a mist, to a quality of shining belonging to that 
particular part of the mist, which by chance happened to be 
situated where the star is seen. If then the former nebulosity 
of the two stars which have ceased to be nebulous can only be 
ascribed to an effect of the transit or penetration of their light 
through nebulous matter which deflected and scattered it, we 
have now a direct proof that this matter can exist in a state of 
