the Negro , being a defence against the sun's rays. 5 
The same experiment was made with a white handkerchief 
loose upon the hand, the heat 83°. In 15 minutes an inflam- 
matory blush was produced over a surface of several inches 
extent, which almost immediately disappeared on withdraw- 
ing the hand from the sun's rays. 
Experiment 8. 
September 12th. The sun's heat at noon 85°. The concen- 
trated rays applied to the back of the hand of a Negro from 
Grenada for 15 minutes, produced no visible effect; at the 
first moment he felt a stab going inwards, but that went off, 
and afterwards he had no pain. 
From these experiments, it is evident that the power of 
the sun's rays to scorch the skin of animals is destroyed 
when applied to a black surface, although the absolute heat, 
in consequence of the absorption of the rays, is greater. 
The same wise providence which has given so extraordi- 
nary a provision to the Negro for the defence of his skin, 
while living within the tropics, has extended it to the bottom 
of the eye, which otherwise v/ould suffer in a greater or less 
degree when exposed to strong light; the retina, from its 
transparency, allowing ir to pass through without injury. 
That the nigrum pigmentum is not necessary for vision, 
but only provided as a defence against strong light, is proved 
by its being darker in the Negro than the European, and 
being of a lighter colour in fair people than in dark, and 
therefore lightest in those countries farthest removed from 
the effects of the sun. 
In the monkey it is dark, and in all animals that look 
upwards. 
In all birds exposed to the sun's rays the nigrum 
