1 122 BULI^ETIN OF THE BUREAU OF FISHERIES. 



able to approach near enough for purposes of accurate observation with the naked 

 eye. If field glasses are used the mirrors in the reflecting water glass should not 

 be ordinary glass mirrors silvered on the back, since these produce double images 

 which interfere to a slight extent with the working of field glasses. They should 

 be of metal or of glass silvered on the surface, yielding a single image. 



The principle of the reflecting water glass is shown in the diagrammatic 

 figure 4, in section from the narrower side. The glass is seen entire in figure 3, 

 plate II. 



Photographic methods. — The writer has elsewhere (1908) described fully 

 the methods which he and others have devised for the photography of aquatic 

 animals and need here only outline these. 



Photographing fish in aquaria is a method often of great value in obtaining 

 records of their habits. The method is fully described in the papers cited in 

 Reighard, 1908. Figure 4, plate cxv, shows the male of the common shiner 

 (Notropis cornutus) with the details of scales, fin rays, and pearl organs clearly 

 brought out. It was made with a reflecting camera from a specimen in an 

 aquarium. Other examples of such work are figures 10 to 16, plates cxviii, 

 cxix, and cxx. 



Fish and fish habitats may also be photographed, by the methods already 

 described by the author (1908), while the fish remain in their natural sur- 

 roundings. To accomplish this two modes of procedure are available, as 

 follows : 



(a) The camera may be pointed from the air at the object beneath the 

 surface of the water and the photograph taken through the surface of the water. 

 In order to accomplish this it is nearly always necessary to cut off by a suitable 

 screen the light reflected into the camera from the sky and other distant 

 objects. This light is usually stronger than that which comes from the subject 

 to be photographed, and if it enters the camera it affects the photographic 

 plate in such a way as to obliterate the image formed on it by any object 

 beneath the water's surface. One method of using such a screen and the 

 results are shown in figure 5, plate cxvi. Here a dark screen stretched on 

 a wooden frame is held by hand in an oblique position, so as to cut off the 

 reflected light from the sky while allowing the full sunlight to fall on the object 

 to be photographed. The object is in this case the nest of a small-mouth 

 black bass. The large stones which form the bottom of the nest are shown 

 clearly within the reflected image of the screen. Outside this image the 

 reflected light from the sky has entered the camera so that in the picture almost 

 nothing is visible beneath the water's surface. 



Figure 6, plate cxvi, is from a photograph obtained by this method and 

 shows brook lampreys in the act of spawning. Sometimes it is necessary to use 

 not only a screen to cut off the reflected light, but at the same time a water 



