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



C, the limit of green and blue, is not so clearly marked as the 

 rest ; and there are also, on each side of this limit, other distinct 



Fig. 3. 



9 



AB 

 BD 





 P 

 DG 



EH 



dark lines, / and g, either of which, in an imperfect experiment, 

 might be mistaken for the boundary of these colours. 



" The position of the prism in which the colours are most 

 clearly divided is when the incident light makes about equal 

 angles with two of its sides. I then found that the spaces A B, 

 BC, CD, DE, occupied by them, were nearly as the numbers 

 16, 23, 36, 25." 



In the light of the subsequent careful examinations of the 

 spectrum made in 1814-15 by the celebrated optician Fraun- 

 hofer of Munich, we can ascertain what Wollaston really saw. 

 Wollaston, in short, only observed imperfectly the dark lines of 

 the spectrum, now known as Fraunhofer's lines ; but he ima- 

 gined he saw a spectrum so pure (that is, formed by such a 

 degree of dispersion) that it became divided into four distinct 

 and separated "primary divisions." He at once inferred, and 

 erroneously, that Newton's analysis of the sun's light was 

 false — that no orange or yellow exists in the spectrum, but be- 

 tween the red and the blue there exists only a "yellowish 

 green." Further on we shall see how Young made a similar 

 but even greater error in his description of this observation. I 

 imagine that when Wollaston's sharp eye caught the glimpse of 

 the divided spectrum, he naturally thought he saw in those 

 divisions uniform colours. It was a natural mistake, and only 

 too readily made, by reason of his mind imagining that the 

 dark lines were the dividing lines of the pure simple colours of 

 the solar spectrum. 



In the figure illustrating Wollaston's observation, I have 

 placed alongside of his lines A, B,/, g, D, and E the corre- 

 sponding Fraunhofer letters B, D, b, F, Gr, H, thus giving 

 the reader a clear idea of what Wollaston really saw. Wollas- 

 ton's line u B, between the red and the green," and which he 

 says "in a certain position of the prism is perfectly distinct," 



