200 Mr. BowporN on Light, and the Wajie of Matter : 
the imagination ; and render human calculation inadequate to 
exprefs the precife degree of them, or the inconfiderablenefs of 
the momentum of thofe particles. 
This inadequatenefs is particularly applicable to the forego- 
ing calculation : which was purpofely made.on the difadvanta- 
geous principles affumed in it, to fhew, that even on fuch prin- 
ciples, the momentum of light could produce no vifible mo- 
tion in the fmalleft bodies, that fall under our notice. But had 
the calculation been founded on the fate of the fun's light re- 
fle&ed from one of the planets, for inftance, the Georgium 
Sidus, lately difcovered by Mr. Herfchell, the refult would 
have been widely different ; and we fhould, in that cafe, have 
had a jufter idea of the momentum. The light reflected to the 
earth from that planet, whofe mean diftance from the fun is 
faid to be 5,000,000,000 miles, is fo extremely attenuated, 
that the momentum of a particle of it, transferred to a body, 
weighing a millionth part of a grain, would communicate to 
_ it fo fmall a degree of motion, that it would require millions 
of ages for that body to move the diminutive: ‘part of an inch 
mentioned in that calculation. 
If thefe obfervations be juft, it is apprehended they thew, 
with fome degree of evidence, that a particle of light, notwith- 
ftanding its prodigious velocity, cannot by its impulfe remove 
other bodies, or difplace even the fineft microfcopic duft ; and 
that the doctrine objected to, may be true, notwithftanding the 
the firft of the two objections, which have been made to it. 
The fecond propofition, containing the other objeétion, is, 
thatin cafe there are particles of matter, called light, conti- 
nually driven off from the fun’s furface, the fun muft be ex- 
ceedingly diminifhed by fuch a wafte of matter ; and the pla- 
nets, 
