66 BULLETIN OF THE BUREAU 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 subaquatie 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 subaquatie 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 imstantaneous 
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 vor 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 
