SEEN WITH THE EYE OF A FISH 23 



ticular object on his body, I nailed a row of miniature 

 sleepers from a toy electric railway, on a piece of tin, 

 and, placing the tin under the water, I fixed two sheets 

 of glass, one inch apart, so that they were supported on 

 the sleepers. A dace introduced between the sheets of 

 glass soon rested on the bottom, and reflected each 

 single sleeper on its body, as shown in the photograph. 



To demonstrate how the dace reflects the tone and 

 colour of his surroundings, I constructed a wooden tank, 

 with one side of glass. The first illustration of this tank 

 shows a dace in the centre, lighted from above and from 

 in front. The photograph of the dace taken by this 

 illumination shows it as a silvery sided fish against a 

 dark background, for the light reaching the side of the 

 fish through the plate glass and eighteen inches of clear 

 water is reflected back ; the other side of the fish was 

 dark, reflecting the dark back of the tank. 



Next, I nailed a rug on the rail above the glass, and 

 carried it over the camera. The glass side of the tank 

 was now as dark as the wooden side, and the dace seen 

 from under the rug appeared by reflection dark against 

 the dark background. From the two illustrations of the 

 dace, photographed in the wooden tank, it will be seen 

 that the dark fish, illuminated only from above, as in 

 nature, is much less conspicuous than the silvery fish. 



Do fish conceal themselves by reflection in a similar 

 manner in their native element ? A glance at the 

 photograph of the two dace swimming free in the obser- 

 vation pond shows how, by reflecting the shade of the 



