Lately M. Bouton has succeeded in making photographs of the bottom of the sea, but he employed the magnesium light instead of electric. M. Bouton describes in La Nature the work ing of his apparatus : " An ordinary photographic camera, whose lens has a fixed focus, is enclosed in a metal box in the form of a rectangular parallelopipedon. Transparent glass plates are arranged in front of the lens and over the finder." Suitable means are provided by which the lens can be uncovered and the plate exposed; also the plates changed. A rubber balloon, filled with air and connected with the metal box con taining the camera, serves to compensate for the water pressure as in the before described appar atus by Regnard. The whole rests upon a strong tripod provided with weights to make it more stable. When used in water too deep for sunlight to penetrate, artificial illumination is necessary. The latter is employed by Bouton in the following manner : "An alcohol lamp, pro tected from the water, is placed on top of a receiver, of about 200 litres capacity, which is filled with oxygen. The lamp is protected by a bell glass, which is firmly secured to the receiver. Op posite the flame is a tube which is connected with a reservoir which is filled with magnesium, which can be blown through the flame in the usual manner. When
the apparatus is submerged, a simple compression of the bulb is necessary to project the magnesium powder into the flame. Three grammes of magnesium may thus be burned. When operating near the shore at a depth of about one metre, no arti ficial light is necessary, and with an exposure of about ten minutes, good pictures may be obtained. For greater depths it is necessary for the operator to descend to the bottom in order to select the view, and to set the apparatus, so that he may be certain that he may secure what he desires to photograph." When operating at a depth of six or seven metres, the exposure should be of thirty minutes' duration. In order to secure sharp pictures the author deems it necessary to employ a color screen in front of the objective, and good results were obtained only in still water. When oper ating by magnesium light, this condition is not altogether necessary, as Bouton obtained good pictures in rough weather. The accompanying cut shows the manner of making a submarine photograph by Bouton's method.
SUBSTRATUM.—An underlying layer.