14
It has been found necessary to follow the author's nomenclature throughout—T.
15
Non-perception of blue.
16
It has not been thought necessary to copy the plates here referred to.—T.
17
That is (according to the author's statement 150. 151.) both tend to red; the yellow deepening to orange as the comparatively dark medium is thickened before brightness; the blue deepening to violet as the light medium is thinned before darkness.—T.
18
Plate 2, fig. 1.