62 BULLETIN OF THE BUREAU _ OF FISHERIES. 



time in opening and closing, and during the period of operation prevents the light 

 from passing through the full opening of the lens. If the time from the instant 

 a diaphragm shutter begins to open until it is closed again is one one-hunredthd 

 of a second, then a considerable part of this time (usually about 40 per cent) is 

 occupied by the opening and closing. The shutter is then wide open and the lens 

 working at its full opening during only a fraction of the one one-hundredth of a second. 

 With the focal plane shutter, on the other hand, if the slot requires a hundredth 

 of a second to pass a given point on the plate, the lens may be wide open during the 

 whole of that time, so that all the light that the lens is capable of passing reaches 

 the plate during the whole of the exposure. For this reason much more rapid 

 exposures may be made with the focal plane shutter than with the diaphragm shutter. 

 Various forms of reflecting camera are in the market, and it is possible to 

 obtain a magazine plate holder, which carries 12 plates, arranged to be changed 

 without removing the plate holder from the camera or inserting the dark slide. 

 Such a camera, with the magazine holder, is shown diagrammatically in section in 

 figure 9. It is surprising that Boutan, when he was seeking some means of focusing 

 his camera under water, did not make use of the idea of the reflecting camera; for 

 by merely inclosing such a camera in a water-tight metal box and arranging it to 

 be operated from outside the box, he would have had a portable apparatus capable 

 of being manipulated under water almost as readily as on land. A reflecting 

 camera was manufactured in New York as early as 1886, and was advertised at 

 that time and represented by a Paris agent. 



THE WATER-TIGHT BOX. 



A 5 by 7 camera of the type just described, with a magazine holder for 12 plates, 

 was used by the writer to obtain submarine photographs at Tortugas, Fla., during 

 the season of 1907. The box (fig. 2, pi. v) to contain the camera was made of gal- 

 vanized iron by a tinsmith. It measures about 17 inches long, 9 inches high, and 10 

 inches wide. The front is closed by a square of plate glass cemented with aquarium 

 cement into a groove formed in the metal. At the top is an opening large enough 

 to permit the camera to pass, bottom first, into the box. To the outside of the rim 

 of this opening is soldered half-inch square brass tubing jointed at the corners into 

 a rectangular frame. The upper surface of this frame is made as smooth and as 

 nearly plane as possible. Eight brass screw-bolts are soldered into holes drilled 

 through this frame. They occupy the positions shown in the figure and the threaded 

 end of each projects about three-quarters of an inch above the frame. The cover 

 consists of a flat sheet of metal bordered by a frame of brass identical with that on 

 the box. This frame is perforated by eight openings through which the screw-bolts 

 pass. From the cover there arises an irregular truncated pyramid of galvanized iron, 

 which incloses the hood of the camera. At the top this is closed by a piece of plate 

 glass. By means of wing nuts on the screw-bolts the cover may be tightly clamped 

 to the box, against an intervening gasket of rubber. 



On the right hand side of the box is a large milled head of brass from which 

 a brass stem passes to the interior through a stuffing box, which prevents the 

 entrance of the water along the stem. At its inner end the stem terminates in a 



