Colour; A Handbook of the Theory of Colour

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...the top halves appear to be the same size as the bottom halves. We have seen above that, by bringing about the fatigue of certain sets of nerves, we can produce an image of an object in a different colour to that it originally represented. These colours are sometimes known as subjective colours, and we can produce them in various ways. For instance, ssssssssss 8888888888 Fig. 63. if a disc of card is painted in alternate black and white sectors, and placed upon the rotating machine and rotated--or black painted upon a white ground--on rotating, the resulting disc will, after a short time, acquire a certain colour according to the speed of rotation; thus a slow rate gives rise to the production of a green hue, while an increase in the rate of revolution changes it to a rose colour. Eood describes a method of observing these subjective colours by viewing the sky through a revolving disc with sectors; with a slow rate of revolution the sky has a red tint, with a higher rate of revolution a bluish-green tint was obtained in the centre, the outer portion being purple. The passage of a current or shock of electricity through the eye gives rise to the production of subjective colours, which vary with different persons; while persons who have partaken of santonihe see white objects in various colours, the violet end of the spectrum being invisible to them. Colour Blindness.--Many persons are deficient in colour sense. This is independent of the fact that much confusion about colours results from the very defective nomenclature which prevails. The defect referred to is where there is an actual want of perception of certain colours; for instance, a person may be unable to distinguish between a red and a green. This was the case with the eminent chemist John Dalton, t...