relating to the sidereal part of the Heavens. 263 
obtrude themselves, even in greater number, on account of 
the increased space of the more distant regions of their situa- 
tion. 
From stars mixed with nebulosity we are now to direct our 
attention to the purely sidereal part of the heavens ; and as 
stars are the elementary parts of sidereal constructions, it will 
be proper to review what we know of their nature. Having 
already entered upon this subject in a former paper at some 
length,* I shall only give a few additional observations, with 
a summary outline of the former arguments. 
The intensity of the light of a star of the first magnitude 
may be compared with solar light, by considering, that if the 
sun were removed to the distance at which w'e generally ad- 
mit the brightest stars to be from us, its visible diameter could 
not exceed the 215th part of a second; and its appearance 
therefore would probably not differ much from the size and 
brightness of such stars. By reversing this argument we 
shall be authorised to conclude, from analogy, that stars, were 
they near enough, would assume the brightness, and some of 
them perhaps also the size, of the sun ; and the consequences 
that have been drawn from the observations given in my pape^ 
on the nature and construction of the sun, may be legitimately 
applied to the stars ; whence it follows that stars, although 
surrounded by a luminous atmosphere, may be looked upon 
as so many opaque, habitable, planetary globes ; differing, 
from what we know of our own planets, only in their size, and 
by their intrinsically luminous appearance. 
They also, like the planets, shifie with differently coloured 
liffht. That of Arcturus and Aidcbaran for instance, is as 
** Phil. Trans, for 17B5, page 68. 
