260 » A, M. Mayer—History of Young’s 
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 
dark lines, f and g, either of which, in an imperfect experiment, 
might be mistaken for the boundary of these colours. 
: osition 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 AB, 
BC, CD, D £, occupied by them, were nearly as the numbers 
wae 2 2 
when Wollaston’s sharp eye caught the glimpse of the divided 
spectrum, he naturally thought he saw in those divisions unt- 
form colors. It was a natural mistake, and only too readily 
the orange and yellow, and well know to be caused by the re- 
versal of the bright yellow light of sodium vapor. No one, 
however, could now say, after an examination of the spectrum 
as observed by Wollaston, that the line D divides the red from 
the green. Wollaston also calls his D and E lines (the @ an 
H lines of Fraunhofer) as “the two limits of the violet;” we 
now know that G is really on the indigo and that H is within 
the limits of the violet. 
or a more satisfactory comparison of the colors of the solar 
spectrum as observed by Wollaston and Fraunhofer, I give be- 
low the following table. Fraunhofer’s results are taken from 
his colored figure of the spectrum. Both spectra are from flint 
glass, and their lengths are supposed divided into 360 equal parts. 
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