Erasmus Darwin's visual experiments

This image is from Erasmus Darwin's book "Zoonomia" (an edition from 1800). In the first part of the book, the grandfather of Charles Darwin explains some characteristics of the human visual system, and suggest several experiments to the reader. The figures are hand coloured.

Explaining the rainbow

In his 1888 book "L'atmosphère. Météorologie populaire", Camille Flammarion used this beautiful engraving to explain the formation of the rainbow.