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But, as this Caufe of the Diverfity of Colours, which 
we have afligned, feems to be the mod fimple, and 
eafily effedted, like the Operations of Nature con- 
ftantly obfervable in other Things, fo it is mod con- 
fident with the Dodtrine of Colours in many other 
refpefts ; for, were not our Colours to proceed from 
the Parts under the Epidermis , which are always of 
the fame Colour in all People of the mod different 
Complexions ; but the Skin was to be a folid opaque 
Body, which refle&ed our Colours from its Surface, 
like mod other coloured Bodies; we fhouid then, in 
all Probability, have People of all the different Co- 
lours in the Rainbow, and that in one and the fame 
Nation ; for the Skin is feldom obferved to be of 
the fame Thicknefs and Denfty in different Perfons 
of the fame Nation : But Sir Ifaac Newton fhews 
us, that thofe Bodies, whofe Colours proceed from 
refle&ed Light, when they alter their Thicknefs and 
Denfity, change their Colours, not to a more or lefs 
perfect one of the fame Kind, but to one of a dif- 
ferent Kind ( a ) : Thus a thin Plate of Talc, whofe 
Colour proceeds from the Light refledled from its 
Surface, alters its Colour, according to its Thicknefs, 
to all the different primary Colours ; and one of thefe 
Plates, of a pale yellow Colour, laid over another 
one of a blue Colour, turns of a deep Purple ( b ) : This 
would probably be the Cafe of our Skins, was its 
Colour to proceed from refledled Light ; fince there 
are many different Strata of fcaly Plates laid over 
one another in the Skins of different Perfons, even 
id) Newton Ot>t p. 195, <&c. (b) Idem ibid p. 196. 
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