C 239 ] 
As far then as we can guefs at the parallax of the 
fixed ftars from the principles above laid down, we 
may realonably expedt, that it fhould be exceedingly 
fmall even in thofe of the firft magnitude; yet, 
befides the probability, that fome of them may be 
either lefs, or lefs luminous than the Sun, it is not fo 
fmall as to leave us altogether without hopes, that we 
may fome time or other be able to difcover it in fome 
of them ; for I think it is not impracticable to con- 
ftrudt inftruments, capable of diftinguifhing even to 
the 20th part of a fecond, provided the air will 
admit of that degree of exaftnefs; but fuch inftru- 
ments muft be upon a plan a good deal different 
from thofe hitherto made ufe of, as they would other- 
wile be not only vaftly too expenfive, but alfo much 
too great and unweildy to be of any ufe. 
But whatever room there may be to hope, that 
we may fome time or other be able to difcover the 
parallax of a few amongft the fixed ftars, yet at the 
lame time it feems probable, that we fhall never 
be able to difcover any fenfible magnitude in their 
apparent diameters, which in Sirius himfelf, if he 
is not of lefs native brightnefs than the Sun, muft be 
conftderably lefs, whatever be his parallax, than the 
affected by thefe fuppohtions, their furfaccs would indeed be more 
or lefs luminous, accordingly as they were, upon this account, lefs 
or greater ; but the quantity of light, correfponding to the fame 
quantity of matter, would {till remain the fame. 
T he apparent distances, at which fateliites would revolve about 
any ftars, would be equal to the femiannual parallaxes of thofe 
ftars, feen from plane. s revolving about the Sun, in the fame 
periodical times with themlelves, fuppoiing the parallaxes to be 
fuch, as they would be, if the liars were of the fame fize and 
dcnfity with the Sun. 
4 hundredth, 
