PHILOSOPHICAL 
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TRANSACTIONS. 
I. On the black rete mucosum of the Negro , being a defejice against 
the scorching effect of the sun's rays . By Sir Everard 
Home, Bart. F. R. S. 
Read November g, 1820. 
To ascertain the use of the black colour of the rete mucosum 
in the Negro, has occupied the attention of many physiolo- 
gists ; and I confess that this subject formed the first investi- 
gation in which I ever engaged. Fruitless, indeed, were my 
attempts ; and when I learnt that black surfaces absorbed 
heat, and raised the temperature several degrees beyond 
any others, I gave the matter up in despair. Two years 
ago my' attention was again called to this enquiry, upon 
being told by our late excellent President, that a silver fish, 
in a pond at Spring Grove, during a very hot summer, 
immediately after some trees by which the pond was shaded 
were cut down, was so much exposed to the sun’s rays as to 
have its back scorched, the surface putting on the same ap- 
pearance as after a burn, and rising above the scales of the 
MDCCCXXf . B 
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