COMPOSITION OF LIGHT. 13 



temperature with great rapidity, others but slowly ; some are 

 good, others bad radiators of heat; some absorb it greedily, 

 others allow it to pass freely through their molecular tissues. 

 Thus the sun brings forth an infinite variety of actions and 

 reactions on the surface of the earth, for the atmosphere, the 

 waters, the solid parts of our globe are all variously affected 

 by his rays ; and as all bodies are constantly endeavouring to 

 equalise their temperatures, it may easily be imagined what 

 numberless interchanges of heat are constantly taking place 

 in all directions over the surface of the globe. But from these 

 perpetual oscillations, from this restless striving towards a 

 uniformity of temperature which can never be obtained (for not 

 a cloud passes, not a sunbeam falls, without creating some 

 new disturbance), arises that magnificent harmony between 

 organic life and the external world of air, water, and earth, 

 which can only have resulted from the design of a supreme 

 regulator. 



If a beam of pure white light, admitted through a small hole 

 in a window-shutter into a darkened room, be made to pass 

 through a triangular prism of glass, it will be disentangled 

 and reduced into a number of splendid colours, similar to 

 those exhibited by the rainbow in all its beautiful gradations 

 of red, orange, yellow, green, blue, indigo, and violet. These 

 primitive tints, which are also called elementary or simple 

 colours, as they are incapable of any further division, will 

 reproduce colourless light, if concentred on one spot by a 

 lens a proof of their being its component parts. 



If the light of the sun were simple, then all bodies would 

 appear to us either black or white, by the absorption or re- 

 flection of its uniform rays, and thus Nature, instead of her 

 wonderful and many-coloured garb, would offer but a few dull 

 and monotonous tints. 



As, however, but few bodies reflect or absorb the entire 

 sunbeam, while the majority retain only a part of the prismatic 

 colours and reject the remainder, which thus become visible to 

 the eye, that charming variety of colours is obtained, which we 

 admire in the glowing purple of the morning and evening sky, 

 in the brilliant reflections of the sea, in the foliage of the trees, 

 in the hues of flowers, in the splendid robes of the animal 

 creation, or in the lustrous tints of the mineral world. 



