[ i35 ] 
greater Quantities, and combined in larger Collec- 
tions ; and thefe Particles, being likewife more com- 
minuted by the Sun, will on that account be black, 
as happens to Oil when well boiled. 
From what we have laid above about the imme- 
diate Caufesof the Colours of the Skin, it will ap- 
pear, that thefe feveral EffeCls of the Sun’s Heat con- 
tribute to make it of a darker Colour ; and no one 
will doubt, I believe, but that all of them, confpiring 
together, may make it quite black. 
To thefe, perhaps, might be added another EffeCt 
of the Sun’s Power, a peculiar Necrojis of the Epi- 
dermis, occafioned by the forcible Vibrations, Con- 
tractions, and Exficcations of its Fibres by the Sun- 
beams, which caufe it to turn black, as thefe, or the 
other Parts, do by the Heat of an Inflammation or 
a Fever, in Gangrenes, black Tongues, &c. From 
whence only the nervous Parts of the Skin come to 
be black, and more hard and callous, and lets pellu- 
cid, than the reft j and the Skins of Negroes, beftdes 
their Callofity, become more infenfible than thofe of 
Whites. 
But as there are many Degrees of Whitenefs and 
Blacknefs in the Colours of the People in the World, 
depending upon the different Denfities and Thick- 
neffes of their refpeCtive Cuticles, as we have above 
(hewed, it may not be improper, in the next place, 
to inquire into the more peculiar Caufes 'of this 
Diverfity, which will be found to be fuch as increafe 
or diminifh the Power of the Sun’s Heat, or its In- 
fluence on the Body ; by which the only material 
Objeftion that has been brought againft this Propo- 
rtion may be anfwered ; viz. that the Sun’s is not 
S the 
