. [ 2 4I ] ■ 
we can only fuppofe them, at a medium, to be equal 
in lize to the Sun, this being the heft means, which 
we have at prefent of forming fome probable con- 
jedture concerning the extent of the vifible univerfe. 
That we may be the better enabled to do this, it 
feems to be an objedt worth the attention of Aflro- 
nomers, to enquire into the exadt quantity of light, 
which each liar affords us feparately, when compared 
with the Sun; that, inftead of diftributing them, as 
has hitherto been done, into a few ill defined claffes, 
they may be ranked with precifion both according 
to their refpedtive brightnefs, and the exadt degree 
of it. 
A catalogue of the ftars formed upon this, plan, 
would anfwer feveral good purpofes ; for, befides 
giving us a more juft and certain notion of their 
general diftances, it would perhaps help us, efpecially 
if the parallax of a few amonglf them fhould be 
difeovered like wife, to trace fome analogies in their 
fttuation, which might enable us to determine both 
their diftances, and other circumftances relating to 
them, with ftill more probability; and it would be a 
ftanding regifter, by which future Aftronomers might 
inform themfelves of many variations, of which we 
are now ignorant for want of an ancient regifter of 
that kind. 
From what has been faid above, I think it is very 
probable, that we fhall not be a great way from 
the truth in eftimating the whole parallax of Sirius 
at one fecond, fuppoftng him to be of the fame fize 
and native brightnefs with the Sun; this therefore I 
fhall aflume as a ftandard, till fome better experiments 
fhall inform us more exadlly of the quantity of his 
Vol. LVII. I i light* 
