96 REFLECTED AND TRANSMITTED LIGHT. _ a= ^ / * 



If the -water were perfectly smooth, then the image would 

 be perfectly clear and distinct. But this can never be, as 

 the surface of water is never perfectly smooth. It is ruf- 

 fled by slight movements of the air in the calmest days. 

 In this case, the ripples made by the swimming of the ducks 

 affect it - and even the swimming of fishes or of frogs, far 

 below, is sufficient to produce some change in the surface, 

 and to prevent absolute repose. 



When water is deep and the bottom is dark, we see the 

 reflection most clearly, for then there is very little trans- 

 mitted light coming up through to disturb it ; but when 

 the water is shallow, and the objects on the bottom are 

 bright and clear, then we see the reflection indistinctly or 

 not at all, for the reflected rays are overpowered by those 

 which are transmitted from below. 



These are, then, the fundamental principles on which the 

 ghost illusion depends, namely, that any material which is 

 at once transparent in substance, and also plane and pol- 

 ished upon its surface, like a plate of glass, for example, 

 will transmit and also reflect light at the same time, so that 

 you can see objects through it and objects reflected in it 

 together, and the comparative distinctness with which you 

 see them depends upon the comparative intensity of the 

 light with which they are respectively illuminated. 



