go ESSAYS AnD OBSERVATIONS 
little exceeding that which muft be aferi- 
bed to its colorific parts, according to Sir 
Ifaac Newton’s theory? But, how can it 
cohere into a continuous leaf, fo asto leave 
no vifible pores, unlefs there be many of 
its component particles contained in. its: 
thicknels? 
Quer. XVIII. Wen one looks fted- 
faftly at Sirius, or any bright ftar not 
much elevated above the horizon, its co- 
lour feems not to be conitantly white, 
but appears tinctured, at every twink- 
ling, alternately with red and blue: To 
what is this appearance owing? Is not the’ 
fevaration of colours by the refraction of 
the atmofphere too fimall to be percei- 
ved? 
vER. XIX. Boprers become black 
by burning: becaufe they are reduced * 
into very fmall parts: But, whence is it, 
t hat moft bodies, when further burned to 
afhes, aflume a grey or whitith colour? 
U FRLRX. Sine E the caufe of black- 
nefs in bodies is. the fmallnefS of their 
ee 
Cae 
* Newt. optics, book 3. part 2, prop. 7. 
trant 
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4 > eek ae etn eee te il ee ii i OO Oe, 
