60 BULLETIN OF THE BUREAU OF FISHERIES. 
A NEW SUBAQUATIC APPARATUS. 
When a camera for subaquatic use is made after the ordinary type the box 
must be securely closed before submerging it in order to protect the lens and the 
plates from the action of the water. While the camera is under water it is not 
possible to remove the plates or plate holder in order to substitute a ground glass 
for them. It is therefore impossible to focus, and the camera must be adjusted to 
the desired focus before immersing it. This was the method adopted by Boutan 
in his third apparatus. It would be possible to construct a camera that might be 
focused under water by means of a focusing scale such as is provided in those hand 
sameras arranged to be focused without the use of a ground glass, the operator 
estimating the distance of the object and then setting the camera for a corresponding 
division on the focusing scale. This 
method is of value for more distant ob- 
jects and with rather slow lenses of 
great focal depth. When very rapid 
lenses are focused on near objects only 
those objects are in focus that lie nearly 
inone plane. Thusavery accurate ad- 
justment of the camera is necessary in 
order to bring any near object into sharp 
focus, and this is not possible when the 
distance of the object must be estimated 
and the focusing accomplished by means 
of ascale. Insubaquatic photography 
the objects to be photographed are all 
near and if instantaneous work is to be 
done the lens must be very rapid. It 
is therefore important to be able tofocus 
Fic. 9.—A reflecting camera shown in section, with magazine accurately we the ground glass under 
plate holder attached. gl, ground glass; hh’, hood; J,lens; m, Water, and this might be accomplished 
ETO LI BOSH Omid iting £OCUBINE UL ant LEONE SOA by using two identical cameras (twin 
during exposure; p, sensitive plate; r and 7’, rollers of focal is 6 4 
plane shutter; s, the shutter; s7, slot in shutter; z, hinge on camera) united soas to form one instru- 
which mirror turns; yy y’, ray of light traversing the lens and ment. One of these contains the plates 
reflected from the mirror to the ground glass. 3 & 
and has a lens provided with ashutter. 
The other camera carries the ground glass. The same focusing mechanism operates 
both cameras, so that when a sharp image is formed on the ground glass of the one an 
identical image strikes the sensitive plate in the other when the shutter is operated. 
One of the cameras serves merely as a focusing finder of full size. A camera of this 
type properly constructed of metal could undoubtedly be used successfully under water, 
though it has the disadvantage of being unnecessarily cumbersome and expensive. 
THE CAMERA. 
All of the advantages of the twin camera are to be had by using a reflecting 
camera, which is at the same time both lighter and less expensive. The principle 
of the reflecting camera is shown in figure 9, which represents diagrammatically 
