46 BULLETIN OF THE BUREAU OF FISHERIES. 



portions of distant objects, of natural size, magnified or reduced; and the light 

 from them entering the camera affects the photographic plate in such a way as 

 to obliterate the dimmer image of any object lying beneath the water. At the 

 same time the light from the submerged object is refracted in various directions 

 as it emerges into the air through the irregular surface of the water, so that its 

 image as formed on the retina or ground glass is neither sharp nor steady. 



From the foregoing discussion it appears that attempts to photograph sub- 

 merged objects with a camera placed in air can result in only partial success, and 

 this but rarely. Failure is due to the fact that the photograph is made through 

 the surface of contact of two media, water and air, of very different refractive 

 powers. If this surface is not perfectly smooth the light from an object beneath 

 it is, upon emergence, refracted unequally at different parts of the surface and can 

 not form a clear image on the ground glass. Whether the water is smooth or rough 

 its surface reflects a part of the light which strikes it, and thus acts as a mirror. 

 This reflected light makes it impossible, except under unusual conditions, to obtain 

 photographs of submerged objects. To obtain such photographs the surface of 

 the water must be smooth and light reflected from it must not enter the camera. 

 Two modes of procedure suggest themselves: 



(1) The camera may remain above the surface of the water. In that case the 

 surface of disturbed water must be rendered smooth and the light from objects 

 above water must be prevented from striking its surface at such angles as to enter 

 the camera in sufficient amount to fog the plate. Methods devised by the writer 

 for accomplishing these two results are taken up and illustrated in the following 

 section. 



(2) The camera may he placed heneath the surface of the water, so that this 

 surface does not intervene between the camera and the object to be photographed. 

 The light which enters the camera is therefore neither refracted nor reflected at 

 this surface, and images may be obtained on the ground glass as clear and steady 

 as though viewed through air alone. Methods of the writer and others for accom- 

 plishing this are described and illustrated in the final section of this paper. 



A NEW METHOD OF PHOTOGRAPHING SUBMERGED OBJECTS WITH THE CAMERA 



ABOVE THE SURFACE. 



It was pointed out in the preceding section that if the camera with which sub- 

 merged objects are to be photographed is to remain above the surface of the water 

 means must be found (1) greatly to reduce the amount of reflected light entering 

 the camera from the surface of the water, and (2) to render the surface of the water 

 smooth. We may consider first the case in which the surface of the water is smooth, 

 so that it is necessary merely to minimize surface reflection. 



The method to be described is best adapted to objects in water not more 

 than 2 or 3 feet deep, and the best results are obtained when the water is less 

 than a foot in depth. Any type of camera may be used, but since the objects to 

 be photographed are necessarily quite near the camera they are out of focus with 

 a fixed-focus camera, so that the best results are obtained when the camera is one 

 that can be focused. Since the objects to be photographed are usually in motion, 

 and since the surface of the water may at any time be roughened by a puff of wind, 



