BY WAY OF INTRODUCTION 13 



obvious; here, however, the body of the water- 

 hen under the water is dark green in colour, 

 while the reflection is of a lighter shade. The 

 explanation as to why the water-hen appeared 

 first red and then green is as follows : I placed 

 in the pond immediately in front of the glass 

 a large sheet of tin, painted red. In the centre 

 of this tin I cut a small hole through which I 

 photographed the bird on a Lumiere colour plate. 

 Next I took the same bird to a pond overgrown 

 with confervae and green vegetation. The por- 

 tion of the black-plumaged bird below the 

 surface now appeared green by reflection, as 

 shown in the lower illustration. 



It must be realised that the foregoing 

 remarks only apply when the anemone, gull or 

 water-hen are viewed from under the water. 

 The white anemone seen in the sea from a boat 

 may appear white, even if under a shelving rock, 

 because it reflects the rays of light from the point 

 of view of the observer. But to the observer 

 under the water, on a level with the anemone 

 and with the top light cut off, it appears green, 

 red or any other colour that may be reflected 

 from its surroundings. 



In the same manner, if from the bank of a 



