C 426 ] 
denfity upon the furface of the orbis magnus h 
fhould be more than ith part of the denfity of our 
air. When fubflances of different fpecific gravities, 
as a piece of gold and a piece of cork, defcend, in 
the exhaufled receiver, with equal velocities, and fall 
equal heights in the fame time, it is obvious, that the 
denfity of the medium, through which they fall, bears 
nofenfible proportion to the denfity even of the lighter 
fubftance. The medium through which fuch lub- 
dances fall, in a tranfparent glafs receiver, is compofed 
of fome fmall portion of rarified air, and, to all ap- 
pearance, of the fame quantity of light, as the re- 
ceiver contains before exhauflion. For the quantity 
of light, in a tranfparent receiver, can by no means 
fuffer any diminution, by the action of the air-pump. 
The denfity of the light therefore, in our air, is cer- 
tainly too fmall to bear any fenfible proportion, to 
that of gold or even of cork. And the denfity 
of cork bears, though a great, yet a finite and 
a fenfible proportion to that of the atmofphere ; be- 
caufe in air gold and cork do not defcend with equal 
velocities. Hence, I think, I may conclude with the 
greatefl certainty, that the denfity of the fun’s light 
at the earth, or upon the furface of the orbis magnus, 
is too fmall to bear any fenfible proportion to the 
denfity of common air j and I lhall hardly under- 
rate the denfity of the light, if I reckon it only 
P art of the denfity of the air, or T __2___th 
part of the denfity of common water. Suppole this 
1 By the furface of the orbis magnus, I mean to denote a 
particular place in abfolu-te fpace, namely the furface of that 
iphere which is concentric with the Oi 2nd hath the earth’s 
mean diftance from the O (or its femidiameter. 
to 
