COMMON THINGS COLOUR. 



a series of seven spaces, vividly coloured, the lowest space being 

 red, E; the next in ascending, orange, o; and the succeeding 

 spaces, yellow, Y ; green, G ; light blue, B ; dark blue or indigo, 

 I ; and, in fine, violet, v. 



These several coloured spaces are neither equal in magnitude 

 nor uniform in colour. The red space R, commencing at the 

 lowest point with a faint red, increases in brilliancy and in- 

 tensity upwards. The red, losing its intensity, gradually melts 

 into the orange, so that there is no definite line indicating where 

 the red ends and the orange begins. In the same manner, the 

 orange, attaining its greatest intensity near the middle of the 

 space, gradually melts into the yellow ; and in the same manner, 

 each of the succeeding colours, having their greatest intensities 

 near the middle of the spaces, melts towards its extremities into 

 the adjacent colours. 



The proportion of the whole length occupied by each space will 

 depend upon the sort of glass of which the prism is composed. 

 If it be flint-glass, and the entire length M N be supposed to con- 

 sist of 360 equal parts, the following will be the length of each 

 succeeding colour, commencing from the red upwards. 



Red 



Orange 



Yellow 



Green . 



Blue 



Indigo 



Violet 



56 

 27 

 27 

 46 

 48 

 47 

 109 



360 



It appears, therefore, that the ray of light P Q, after passing 

 through the prism, is not only deflected from its original course 

 r Q P', but it is resolved into an infinite number of separate rays- 

 of light which diverge in a fan-like form, the extreme rays being 

 L K and L K', the former being directed to the lowest point of the 

 coloured space upon the screen, and the latter to the highest 

 point. The coloured space thus formed upon the screen is called 

 the prismatic spectrum. 



18. From this experiment the following consequences are 

 inferred : 



1. Solar light is a compound principle, composed of several 

 parts differing from each other in their properties. 



2. The several parts composing solar light differ from each 

 other in refrangibility, those rays which are directed to the 

 lowest part of the spectrum being the least refrangible, and those 

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