6 Sir Everard Home on the rete mucosum , 
pigmentum is black. In fishes, the basking shark, which lies 
upon the surface of the ocean, has a nigrum pigmentum. The 
turbot and skate, which lie upon banks of sand in shallow 
water, have nigrum pigmentum. 
In all ruminating animals and birds of prey, there is a lucid 
tapetum at the bottom of the eye. 
The owl, that never sees the sun, has no nigrum pigmen- 
tum. 
The mackarel has the bottom of the eye lucid as quick- 
silver. 
The Coup de Soleil, met with in the West Indies, the effects 
of which I have seen, I attribute to the scorching effect of 
the sun's rays upon the scalp. 
The Egyptian ophthalmia I consider to be the effect of the 
sun's rays, and the glare of reflected light. 
I have stated the fact of the scorching power of the sun's 
rays being destroyed when they are applied to black surfaces, 
but have not gone farther. Sir Humphry Davy, to whom I 
showed these observations, immediately explained it. He 
said the radiant heat in the sun's rays was absorbed by the 
black surface, and converted into sensible heat. 
