too evanescent to be arrested, they were banished into the region of phantoms, and under this idea have been very variously described.
2.
Thus they are called colores adventicii by Boyle; imaginarii and phantastici by Rizetti; by Buffon, couleurs accidentelles; by Scherfer, scheinfarben (apparent colours); ocular illusions and deceptions of sight by many; by Hamberger, vitia fugitiva; by Darwin, ocular spectra.
3.
We have called them physiological because they belong to the eye in a healthy state; because we consider them as the necessary conditions of vision; the lively alternating action of which, with reference to external objects and a principle within it, is thus plainly indicated.
4.
To these we subjoin the pathological colours, which, like all deviations from a constant law, afford a