14 ANIMAL LIFE UNDER WATER 



stream a water-hen is seen to dive into the water, 

 the bird appears a mass of silver, for the air 

 bubbles in the feathers reflect the light from 

 above. I have shown how, seen from below in 

 the area of total reflection, this bird is concealed 

 by reflection. 



Though a white object on the surface, seen 

 in the area of total reflection, is concealed, this 

 very reflection causes it to become conspicuous 

 as soon as it is seen in the area of the circular 

 " window." 



Examine the plate opposite. On a pond 

 specially constructed for surface observation a 

 white saucer was floated down on the water 

 towards the observer. Seen from the chamber, 

 the surface of the water reflected the green 

 undergrowth in the pond; the saucer did the 

 same, and was, therefore, lost to view. The 

 position of the saucer in the area of total reflec- 

 tion can be detected by the white ring where 

 the saucer cuts the surface. 



As soon as the saucer floated into the circle 

 it will be seen how prominent it appeared, for it 

 continued to reflect the green undergrowth and 

 is seen as a dark silhouette against the light of 

 the sky. 



