122 Prof. A. M. Mayer on the History of Young's 



laston's supposed complete analysis of the sun's light into red, 

 greenish blue, and violet colours separated from each othor in 

 the spectrum by dark spaces. 



We hear no more from Young about his theory of colours 

 until 1807, when he published the first volume of his celebrated 

 work, 'A Course of Lectures on Natural Philosophy and the 

 Mechanical Arts ' *. On page 439 ct seq. of this work Young 

 gives a concise statement of his views on the analysis of the 

 sensations of colour, and supports these views with conclusive 

 experiments with rotating coloured disks ; but, strange to Bay, 

 he omits from this account of his theory all mention of the 

 physiological explanation of it which he gave in the Baker ian 

 Lecture of 1801. The following extracts from the ' Natural 

 Philosophy ' give all that it contains on the theory of colours. 

 The italics are our own. 



" It has generally been supposed, since the time of Newton, 

 that when the rays of light are separated as completely as pos- 

 sible by means of refraction, they exhibit seven varieties of 

 colour related to each other with respect to the extent that 

 they occupy in ratios nearly analogous to those of the ascend- 

 ing scale of the minor mode in music. The observations were, 

 however, imperfect, and the analogy was wholly imaginary. 

 Dr. Wollaston has determined the division of the coloured 

 image or spectrum in a much more accurate manner than had 

 been done before. By looking through a prism at a narrow line 

 of light, he produces a more effectual separation of the colours 

 than can be obtained by the common method of throwing the 

 sun's image on a wall. The spectrum formed in this manner 

 consists of four colours only, red, green, blue and violet, which oc- 

 cupy spaces in the proportion of 16, 23, 36, and 25 respec- 

 tively, making together 100 for the whole length, the red being 

 nearly one sixth, the green and the violet each about one fourth, 

 and the blue more than one third of the length. The colour t 

 differ scarcely at all in quality within their respective limits; but 

 they vary in brightness, the greatest intensity of light being in 

 that part of the green which is nearest the red. A narrow line 

 of yellow is genercdly visible at the limit of the red and green 

 but its breadth scarcely exceeds that of the aperture by which 

 the light is admitted, and Dr. Wollaston attributes it to tJu 

 mixture of the red with the green light. There are also several 



* u We have heard it remarked," says Dean Peacock in his ' Life oi 

 Young, " that no writer, on any branch of science which the lectures treat 

 of, can safely neglect to Consult them, so rich is the mine of knowledge 

 which they contain ; and it is a well-known fact that many importani 

 propositions and discoveries have been more or less clearly indicated ir 

 them, which have only been recognized or pointed out when other philc 

 sophers discovered them independently, or announced them as their own.' 



