606 Messrs. Aichi and Tanakadate : Theory of 
8. Pernter calculated the colours of the rainbow due to 
the sun, but his calculation was not sufficient to establish the 
above-mentioned results. We repeated the calculation for 
one case. The theory of compound colours being the subject 
of much dispute, there is as yet no settled opinion. But we 
can admit that, excluding the physiological and psychological 
point of view, there are three primary colours, as Maxwell’s 
experiment * shows. For the discussion of the colours of the 
rainbow, we may conveniently take only these three primary 
colours, in such a ratio as to produce white, and proceed in 
the manner indicated by Maxwell. 
We take the primary colours 
A4=6302 x 10-8 em.(Scarlet) 5211x10-Sem.(Green) 4659 x 10-8 em.(Blue) 
corresponding to Maxwell’s 
[24] [ 46 | [64] 
in the ratio 1: 1°62: 1°60, so as to produce white, 
and n = 1302 1-339 t-332: 
whence K=115°30 129° 16 142°70 
D=42°-22 41°°80 41°21 
Thus we obtain the result represented by fig. 2 and fig. 3 
(pp. 609,610), the former corresponding to the case of the point 
source, and the latter to the circular source (2©= 32! mean 
angular diameter of the sun), 7 in both cases being 0:025 em. 
The intensity of the scarlet ray is given by dotted, green by 
broken, blue by full lines, and the sum of the three ‘intensities, 
?. é. the total intensity, by the curve (1), which is compounded 
by the portion of white and the portion of the two primary 
colours. 
For example, in fig. 2 :— 
I at 41°°5 consists of 26 per cent. scarlet, 50 percent. green, 24 per cent. white, 
AQP*5 . 14 os blue, 16. i scarlet, 70 ,, white, 
38° * 26 uy green, 74 ,, blue, es white. 
In fig. 3:— 
I at 41°°5 consists of 27 per cent. scarlet, 47 per cent. green, 26 percent. white, 
40°°5 Fs 25 a blue, 10 7. scarlet, 65 » white, 
38° a 10 ., green, 22 - blue, 68 » white, 
where the angles correspond to SOCO=D—6 in § 2. 
The above calculation shows that in the colours of the 
* Scientific Papers, i. p. 410 (Cambridge, 1890). 
