PHYSICAL anp LITEBARY. 83 
ats red colour will not be fenfibly impair- 
ed. But, to fhew that, in proper circum- 
ftances, the blueifh colour of fky-light may 
be feen on bodies illuminated by it, as it 
is objected fhould always happen*; ex- 
pofe to the fun-beams, on a clear cloud> 
lefs day, a fheet of white paper, and place 
on it any opaque body; you will perceive 
that the {pace of the fhadow, which is il- 
luminated only by the fky, appears re- 
markably blueith, compared with the re({t 
of the paper which receives the fun’s di- 
rect rayse If certain white and black 
paints mixed together produce blue, it 
is becaufe the black is not perfect thade, 
but a dark blue or purple { {.. Any mix- 
ture of whitenefs and true black can only 
form a fainter white or grey, which has 
no more affinity with blue Han with red 
or any other-colour. 
Quer. XV. Is not the opinion which 
Sir Ifaac Newton feems to have had §, 
and, 
* Muffchen. phyfices § 1403. 
t Ibid. § 1172. 
4 Newt, Opt, book 2. part 3. prop. 7- 
§ OP, book 2, part 3. prop. 5+ near the end. 
