Foundations of the Universe 79 



sunlight into its constituent colours, and these various colours 

 will be seen quite readily. Or the thing may be realised in another 

 way. If the seven colours are painted on a wheel as shown op- 

 posite page 280 (in the proportion shown) , and the wheel rapidly 

 revolved on a pivot, the wheel will appear a dull white, the several 

 colours will not be seen. But omit one of the colours, then the 

 wheel, when revolved, will not appear white, but will give the 

 impression of one colour, corresponding to what the union of six 

 colours gives. Another experiment will show that some bodies 

 held up between the eye and a white light will not permit all the 

 rays to pass through, but will intercept some ; a body that inter- 

 cepts all the seven rays except red will give the impression of red, 

 or if all the rays except violet, then violet will be the colour 

 seen. 



The Fate of the World 



Professor Soddy has given an interesting picture of what 

 might happen when the sun's light and heat is no longer what it 

 is. The human eye "has adapted itself through the ages to the 

 peculiarities of the sun's light, so as to make the most of that 

 wave-length of which there is most. . . . Let us indulge for a 

 moment in these gloomy prognostications, as to the consequences 

 to this earth of the cooling of the sun with the lapse of ages, which 

 used to be in vogue, but which radioactivity has so rudely shaken. 

 Picture the fate of the world when the sun has become a dull red- 

 hot ball, or even when it has cooled so far that it would no longer 

 emit light to us. That does not all mean that the world would 

 be in inky darkness, and that the sun would not emit light to the 

 people then inhabiting this world, if any had survived and could 

 keep themselves from freezing. To such, if the eye continued to 

 adapt itself to the changing conditions, our blues and violets 

 would be ultra-violet and invisible, but our dark heat would be 

 light and hot bodies would be luminous to them which would be 

 dark to us." 



