Parallax of the Fixed Stars, 
merely for entertainment, and mull have an exorbitant field of 
view. To a philo fopher this is an unpardonable indulgence. 
I have tried both the fingle and double eye-glafs of equal 
powers, and always found that the fingle eye-glafs had much- 
the luperiority in point of light and diltin&nefs. With the 
double eye-glafs I could not fee the belts on Saturn, which I 
very plainly faw with the fingle one. I would, however, 
except all thoie cafes where a large field is abfolutely neceiTary, 
and where power joined to diltinftnefs is not the foie object of 
our view. 
The application of the different powers of telefcope in 
general is of fame confequence ; and in anfwer to thofe who 
may think I have {trained or over-charged mine, I muft obferve, 
that a fingle glance at the fubfequent h Draconis, y\ Corx>nae r 
and the {tar near p Bootis, with a power of 460, fhewed them 
to me as double {tars ; when, in two former reviews of the 
heavens, I had twice fet them down in my journal as fingle 
{tars, where I ufed only the power of 222 and 22 j, and in 
all probability Ihould never have found them double, had I not 
looked with a higher power. 
We are to remember, that it is much eafier to fee an oh j eft 
when it is pointed out to us than when it falls in our way un- 
expectedly, efpecially if of fuch a nature as to require fome 
attention to be feen at all ; but today no more of other advan- 
tages of high powers, it is evident, that in the refearch of the 
parallax of the fixed {tars they are abfolutely neoeflary. If 
we would diftinftly perceive and meafure or eftimate extremely 
fmall quantities, fuch as a tenth of a fecond, it appears, that' 
when we ufe a power of 460, this tenth of a fecond will be 
no more in appearance than 46^, and even with a power of 
*500 will be but 2' 30", which is a quantity not much more 
than* 
