RELATIONS OF ETHER TO MOLECULES 63 



the moon and planets and all visible objects are seen. 

 Looking at a lamp or the sun reflected in a mirror 

 or in water, the part of the mirror or water where we 

 see the waves reflected regularly can hardly be seen 

 because of the largeness of the portion so reflected, and 

 the comparative smallness of the amount scattered. 

 General objects are easily seen, because the light which 

 shines on them is largely scattered. 



The colour of the rays scattered is determined by the 

 power which substances possess of absorbing some and 

 dispersing others. Were all the rays which fall on the 

 objects of nature scattered, they would be of one universal 

 whiteness. But in different substances there is the 

 power of absorbing certain rays and scattering the rest. 

 This absorbing power is brought clearly into view by 

 transmitting the colours of the spectrum through trans- 

 parent substances, when it is found that each has colours 

 which it allows to pass, and others which it arrests and 

 absorbs. Nitrous acid gas allows the red end of the 

 spectrum to pass, but stops the rays towards the violet 

 end. It is thus shown to absorb the latter and scatter 

 the former, and therefore it is of an orange red colour. 

 When the vapour of iodine is treated in the same way, 

 the orange, yellow, and green rays are arrested, and only 

 the red, blue, and violet are transmitted. The latter 

 only can therefore be dispersed and form the lovely tint 

 of that vapour. Permanganate of potash arrests the 

 yellow and green, and its reddish-violet colour results 

 from the mingling of the others. Potassium bichromate 

 absorbs one part of the spectrum, ammoniated oxide of 

 copper the other, and light passing through both is com- 

 pletely taken up, and so the second is black. If a 

 spectrum be thrown on red paper instead of white, the 

 yellow, green, blue, indigo, and violet are absorbed, 



