85 ESSAYS anp OBSERVATIONS 
moft copioufly, ought they not to appear 
of the fame colour, whether viewed at the 
greateft or leaft difiances? Whence is it 
therefore, that the planets, whofe folid 
parts are probably covered with vegeta- 
bles, and muft therefore reflect great fu- 
periority of green rays, appear almoft in- 
tirely white when viewed from the earth? 
May not this be accounted for, in the 
fame manner as the change of colour ob- 
fervable in earthly objects feen through a 
great tract of the atmofphere? A moun- 
tain covered with the frefheft verdure, at 
the diftance of twelve or fifteen miles, 
looks 
that the idea of extenfion, received by fight, is made up 
of the ideas of indivifibles ; for we receive the idea of ex- 
tenfion by that motion of the eye which is neceflary to di- 
reét its axis to different objects or parts of an object: And, 
it is well Lnown, that the generation of quantity by mo- 
tion is preferred by the beft writers, for this very reafon, 
that it neceflarily excludes the notion of indivifibles. It 
fllould be remembered likeways, that a vilible object ts 
not divided by the eye into a number of contiguous mmé- 
nima vifhilia; for, to whatever mathematical point in 
the object the eye is directed, a minimum vifibile may be 
feen there by means of a certain portion of the object ine- 
mediately furrounding it, 
