with a Conjetfure, fuggefing a Mean, &c. 199 
(lower than the hour-hand of a common clock : which, with 
its greater degree of motion, and much greater quantity of mat- 
ter, does not give to the fmalleft bodies, placed in its way, any 
vifible motion. - 
Preciüon in this calculation is not aimed at, and the nature 
of the fubject does not admit of it: but it is apprehended, it 
will appear fufficiently evident from it, that light, even if its 
velocity were much greater than it is, and its gravity equal to 
that of air, to which, with great difadvantage to the argument, 
it has been, in that refpect, compared, cannot drive before it 
the lighteft duft, or, indeed, give it any fenfible motion at all. 
To the fame purpofe it may be further obferved, that light 
reflected to the eye through a microfcope and prifm, would, it 
is apprehended, exhibit the fame variety of colours, as light 
coming directly from the fun. - In which cafe, the ray fo view- 
ed, (like the candle-ray, which has been confidered as a fingle 
particle only) muft be compofed of a multitude of particles ; 
and be a proof, that the particles of light are inconceivably 
fmaller than the .calculation fuppofes.. This degree of ímall- 
nefs, however, reprefents them to.be of great magnitude, com- 
ared with their real fize : for when we confider, that the fan's 
light is diffufed through the whole folar fyftem, and much be- 
yond it ; and that a part of it, in that antenuated ftate, is re- 
flected to us from the planets, in which reflection it undergoes, 
by its divergence, a further, and an extreme, attenuation : and 
efpecially when we confider the immenfe fphere, throughout 
which the light of the fixt ftars is vifible, particularly thofe of 
them, whofe diftance is fo vaft, that, at oppofite points of the 
earth's orbit, they have no fenfible parallax—the divifibility of 
light, and the proportionable tenuity of its particles, confound 
p" te 
