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from, or absorbed by, fibres lying more deeply. At each reflexion 

 the various kinds of light are reflected in as nearly as possible the 

 same proportion ; but in passing across the fibres, in going and 

 returning, they suffer very unequal absorption on the part of the 

 colouring matter, so that in the aggregate of the light perceived the 

 different components of white light are present in proportions widely 

 different from those they bear to each other in white light itself, and 

 the result is a vivid colouring. 



There are, however, cases in which the different components of 

 white light are reflected with different degrees of intensity, and the 

 light becomes coloured b.y regular reflexion. Gold and copper may 

 be referred to as examples. In ordinary language we speak of a sol- 

 dier's coat as red, and gold as yellow. But these colours belong to 

 the substances in two totally different senses. In the former case 

 the colouring is due to absorption, in the latter case to reflexion. 

 In the same sense, physically speaking, in which a soldier's coat is 

 red, gold is not yellow but blue or green. Such is, in fact, the 

 colour of gold by transmission, and therefore as the result of absorp- 

 tion, as is seen in the case of gold-leaf, which transmits a bluish 

 green light, or of a weak solution of chloride of gold after the addi- 

 tion of protosulphate of iron, when the precipitated metallic gold 

 remains in suspension in a finely-divided state, and causes the mix- 

 ture to have a blue appearance when seen by transmitted light. In 

 this case we see that while the substance copiously reflects and in- 

 tensely absorbs rays of all kinds, it more copiously reflects the less 

 refrangible rays, with respect to which it is more intensely opake. 



All metals are, however, highly opake with regard to rays of all 

 colours. But certain non-metallic substances present themselves 

 which are at the same time intensely opake with regard to one 

 part of the spectrum, and only moderately opake or even pretty 

 transparent with regard to another part. Carthamine, murexide, 

 and platinocyanide of magnesium may be mentioned as examples. 

 Such substances reflect copiously, like a metal, those rays with 

 respect to which they are intensely opake, but more feebly, like a 

 vitreous substance, those rays for which they are tolerably transpa- 

 rent. Hence, when white light is incident upon them the regularly- 

 reflected light is coloured, often vividly, those colours prepondera- 

 ting which the substance is capable of absorbing with intense avi- 

 dity. But perhaps the most remarkable example known of the con- 

 nexion between intense absorption and copious reflexion occurs in 

 the case of crystals of permanganate of potash. These crystals have 

 a metallic appearance, and reflect a greenish light. They are too 

 dark to allow the transmitted light to be examined ; and even when 

 they are pulverized, the fine purple powder they yield is too dark 

 for convenient analysis of the transmitted light. But the splendid 

 purple solution which tney yield may be diluted at pleasure, and the 

 analysis of the light transmitted by it presents no difficulty. The 

 solution absorbs principally the green part of the spectrum ; and 

 when it is not too strong, or used in too great thickness, five bands 

 of absorption, indicating minima of transparency, make their appear- 



