66 BULLETIN OF THE BUKEAU OF FISHERIES. 



A part of the weight attached to the bottom of the box should be movable, 

 so that it could be fastened either toward the front or toward the back. In this way 

 the box could be made to float with the lens pointed at a considerable angle toward 

 the bottom or toward the surface of the water. The operator would then be spared 

 the very considerable effort necessary to hold the box in position when the lens 

 is directed much above or below the plane in which the box floats. 



The purpose of the writer has been to utilize an ordinary reflecting camera 

 for subaquatic work by inclosing it in a suitable water-tight box without in any way 

 lessening its availability for use in air when removed from the box. For use 

 exclusively in water it would be best to design a reflecting camera that could be 

 immersed directly in water without first inclosing it in a box. Such a camera 

 would have to be of metal, water-tight, and would need to have the lens covered 

 by a plate of glass. It would need to have only a small opening at the back on 

 one side for inserting and removing the plates. Such an opening could probably 

 be readily closed by a cover held in place by one or two screws. A camera of this 

 sort, if made rigid enough to withstand the pressure of the water at even moderate 

 depths, would be too heavy for convenient use in air. It would have the advan- 

 tage of simplicity and increased ease of manipulation. 



SOME LIMITATIONS OF SUBAQUATIC PHOTOGRAPHY. 



Turbidity of the water sets a limit to subaquatic photography very much as 

 fog or rain or partial darkness restricts photography in air. The water must be 

 clear that is, apparently free from particles in suspension. If instantaneous 

 work is to be attempted the water must be free from the reddish color that often 

 tinges fresh-water lakes and streams, for the tinge of red or yellow acts as a color 

 screen and greatly lengthens the time necessary for the exposure. 



When one looks from the air into the ocean water at the Tortugas or Bermudas, 

 or into the fresh water of some of our northern lakes, it appears to be as clear as 

 the air itself. When the surface is undisturbed, objects on the bottom at depths 

 of 10 to 20 feet appear with as much clearness as though seen through air alone. 

 The impression is created that such water is actually as clear as air, and that the 

 water would offer no .more obstruction to the vision of one beneath it than air 

 itself. To test this impression the writer constructed a reflecting water glass 

 somewhat like a reflecting camera without the lens. It was a metal tube 2 feet 

 long, and contained two parallel mirrors, set at an angle of 45 with its long axis, 

 and placed one at each end. By putting one end of this with its mirror beneath 

 the surface and looking into the mirror at the other end, he obtained a view of the 

 subaquatic landscape such as a diver obtains when he looks about him through 

 the glass window in his casque. It is surprising to find how limited is the range 

 of one's vision under these circumstances. Even in the clear sea water about 

 tropical islands objects at a distance of 20 feet begin to appear indistinct, and 

 beyond that distance they fade into a bluish haze which constitutes the back- 

 ground. This haze has not the effect of fog or smoke or twilight. It is as though 

 the near distance were limited on all sides by walls of bluish translucent quartz 

 which merged into the near water. From these walls the fish emerge and grow 



