269 
parallax of the fixed stars. 
subtense of o".026, or -J^th of a second, so that a difference of 
parallaxes to the amount of a 40th of a second, existing in 
the two stars of a double star so circumstanced, could scarcely 
escape detection ; and that even much less quantities than 
this, under favourable circumstances, might be rendered sen- 
sible, I think may fairly be concluded, when we consider that 
in this estimate, the data are certainly assumed within bounds. 
No account is here taken of the improvements in the position 
micrometer, which may reasonably be expected, because the 
object at present is only to appreciate the degree of delicacy 
which the method now proposed may lay claim to, with our 
present instruments and habits of observing, and to compare 
it with those which have hitherto been resorted to in the 
investigation of parallax. 
In selecting stars for examination, it appears to me that 
we ought by no means to confine ourselves, by assuming it 
as a universal law that the brightest stars are the nearest to 
us. From what we know of the variety of nature and the 
enormous differences in point of magnitude between the 
bodies of our own system, it seems improbable that the real 
magnitude and brightness of the stars should be confined 
within narrow limits. Their distances are equally undeter- 
mined ; nor have we any reason whatever to conceive these 
two elements related to each other. There is not therefore 
the slightest a priori improbability, in supposing that among 
stars of apparently equal lustre, the greatest diversity of dis- 
tance may exist, or that innumerable of the minutest stars 
visible in telescopes may be nearer to us than any of those 
of the first magnitude ; and consequently, that that delicate 
element in search of which astronomers have exhausted 
Nn 
MDCCCXXVI. 
