134 



PRISMATIC ANALYSIS OF THE SOLAR RAY. 



creation is well shown in the sea. Near the shores we 

 find sea-weeds of the most beautiful hues, parti- 

 cularly on the rocks which are left dry by the tides ; 

 and the rich tints of the actiniae, which inhabit shallow 

 water, must have been often observed. The fishes which 

 swim near the surface are also distinguished by the 

 variety of their colours, whereas those which live at 

 greater depths are grey, brown, or black. It has been 

 found that after a certain depth, where the quantity of 

 light is so reduced that a mere twilight prevails, the 

 inhabitants of the ocean become nearly colourless. 

 That the sun's ray alone gives to plants the property of 

 reflecting colour is proved by the process of blanching, 

 or etiolation, produced by artificially excluding the light. 

 By a triangular piece of glass a prism, we are enabled 

 to resolve light into its ultimate rays. The white pencil 

 of light which falls on the first surface of the prism is 

 bent from its path, and coloured bands of different 

 colours are obtained. These bands or rays observe a 

 curious constancy in their positions : the red ray is 

 always the least bent out of the straight path: the 

 yellow class comes next in the order of refrangibility ; 

 and the blue are the most diverted from the vertex of 

 the prism. The largest amount of illuminating power 

 exists in the yellow ray, and it diminishes towards either 

 end.* It is not uninteresting to observe something like 



Schouw, Grunduzge derPjlanzengeographie. Also his Earth, Plants, 

 and Man; translated by Hent'rey, in Bohn's Scientific Library. 

 Lamouroux, Geographic Physique. The Plant, a Biography : by 

 Schleiden ; translated by Henfrey. Physical Geography : by 

 Mrs. Somerville. 



* Frauenhofer's measure of illuminating power is as follows : 

 At the 22nd degree of the red 0'032 



34th degree of the red 

 22nd degree of the orange 

 ] Oth degree of the yellow 

 42nd degree of the yellow 

 2nd degree of the blue 

 10th degree of the indigo 

 43rd dpQTpe of the violet 



0-094 

 0-640 

 .1-000 

 0-480 

 0-170 

 0-031 

 0-0056 



