[ I2 5 3 
ail over their Body 5 which the Adult do not, except 
in the Eyes, as I had lately an Opportunity of ob- 
Terving: A plain Proof, that the Colour of the 
Skin proceeds from the Colour which is tranfmitted 
thro’ it } and that the Skins of adult Negroes tranf- 
mit no Colour of any Sort. 4. But that the Thick* 
nefs of the Corpus reticular e , the Part which appears 
black in Negroes, by Prop. III. may and does make 
it black, Malpighi give us an Inftance in the laid 
Part, in the Tongue of a Beef, in which it ap- 
pears black, on the middle of the Tongue, where it 
is thick ; but is white on the Edges and Cheeks, 
where it is very thin (a). As for the Manner in 
which this Blacknefs or Opacity is occafion’d by a 
thick or denfe Skin, it will appear from what has 
been faid about the Skins of tawny People : And it 
is very eafy to conceive how the Rays of Light are 
intercepted, in palling thro’ the thick and denfe Skins 
of Negroes, which eafily pervade the thin and rare 
Cuticles of Whites. 
But, as the Skins of Negroes are of a denfer Tex- 
ture than thofe of Whites, they will be more apt to 
refradt the Rays of Light ; for the denfer the Body, 
the greater the Power of Redrafting (b ) ; and the 
greater the Refradtion of any Body is, the more apt 
it will be to abforb the Rays of Light i which is an- 
' other Property of opaque Eodies, by which they 
become black : Torro qtio corpora videantur nigra , 
(a) Malpighi de Lingua, p. 15, 16. (b) Newton Opt. 
Prop. X. 
necejfe 
