On certain colour phenomena caused by intermittent stimulation with white light / by A.S. Percival.
- Percival, A. S.
- Date:
- 1900
Licence: In copyright
Credit: On certain colour phenomena caused by intermittent stimulation with white light / by A.S. Percival. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![On Certain Colour Phenomena caused by Intermittent Stimulation with White Light. By A. S. Pebcival, M.A., M.B. [Read December 15th, 1899.] I would claim your indulgence for bringing a physiologi- cal subject before this section, on the ground that the results of physical experiments are sometimes misinterpreted from a want of knowledge of the factors that contribute to the physiological sensation of colour. As an example I may take the anomalous conclusions reached by Forbes and Young as to the velocity of light. To this point I shall refer again at the end of my paper. It is most important to bear in mind that colour is not a physical term, it is a purely subjective term ; it merely ex- presses the sensation produced by a certain kind of stimulus on a certain kind of cell. Undulations of a frequency about 400 billions per second produce the sensation of red colour in most individuals, while undulations of a frequency of about 700 billions per second produce the sensation of violet. Before light waves reach a colour-seeing organ, they cannot be said to have colour. No one would apply the term nauseous to waves of the sea, though under certain circum- stances they may induce nausea in certain individuals. In books on physics the expression red waves is often con- veniently used as an abbreviation for a set of waves of that period that induces a sensation of red in most individuals. From this use of the word a general idea has arisen that waves of this specific period are the only ones that can give rise to the sensation of red. It is my object in the present](https://iiif.wellcomecollection.org/image/b2247089x_0005.jp2/full/800%2C/0/default.jpg)
