f r40 ] 
there are fome who doubt the fac, though fupported by found 
theory and obfervation. 
Tue following method of determining the quantity of matter 
in’Mars, Venus and Mercury, or any other planet, is certainly 
true in theory. 
. 
Tue axis major of the earth’s orbit as it revolves round the 
common center of gravity of earth and fun=200c0ceco. The 
quantity of matter in the earth we affume=1, that of the fun 
is then 352813, the parallax being allowed 8.6. Now by Prop.: 
60, Book I. of Newton’s Principles, as 47352814: 3,/352513 fo is 
the axis major of the ellipfe round the common center of 
gravity, to the axis major of an ellipfe which would in the 
fame periodical time be defcribed round the fun at reft, and 
is therefore had by the analogy. 
Venvs’s axis major (Coff. El. Aft.) round the common center 
of gravity of the fun and Venus= 144662 by obfervation. Now 
in the fubfefquiplicate ratio of the periodical times of the earth 
and Venus take the earth’s diminifhed axis major to a fourth 
quantity, and we have the axis major of the ellipfe which 
Venus would defcribe round a fixed fun; but we had it by 
obfervation round the common center of gravity. 
Tuen let © = the fun’s quantity of matter, g= that of Venus, 
let m= the axis major of her orbit round the common center 
of gravity, and I= that deduced as above round the fixed fun. 
Then 
