' . f *35 J 
Bouguer in his Trait e d'Optique a ; but as my prefen t 
purpofe does not require any fuch exadtnefs, I fhall. 
deduce it in a more grofs way from faCts already 
well known. I fhall aflume Saturn then in oppoli- 
tion, exclusively of his ring (and when the earth and 
he are at their mean diftances from the Sun) as equal 
or nearly equal in light to the mod luminous fixed 
ftar* Now the mean, difiance of Saturn from the 
Sun, being equal to about 2082 of the Sun’s 
femidiameters, the denfity of the Sun’s light, at 
Saturn, will confequently be lefs than at his own 
furface, in the proportion of the fquare of 2082 (or 
43247 2 4) to 1. If Saturn therefore was to reflect 
all the light, that falls upon him, he would be lefs 
luminous in the fame proportion; but, befides this 
difference in his brightnefs, his apparent diameter, in 
opposition, is at mod but 105th part of that of the 
Sun, and confequently the quantity of light, which 
we receive from him, mud again be diminifhed in 
the proportion of the fquare of 105 (or 11025) 
to i . If we multiply thefe two numbers together, 
we fhall have the whole of the light of the Sun to 
that of Saturn (upon the fuppofition of his reflecting 
all the light, that falls upon him) as the fquare of 
nearly 220000 (or 48,400,000,000) to 1 ; and re- 
moving the Sun to 220000 times his prefent difhnce, 
he would Hill appear at leaf! as bright as Saturn, and 
his whole parallax upon the diameter of the earth’s 
orbit would be lefs than two feconds. This mud 
confequently be aflumed for the parallax of the 
brightell of the fixed ftars, upon the fuppofition that 
their light does not exceed that of Saturn. 
. ' uT, -\tTi OX *5 .‘6 'T -v •* '• 
a This work was publifhed at Paris in 1760. 
H h 2 
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