SUBMARINE PHOTOGRAPHY Water is often so calm and clear that it might seem easily possible for one above its surface to photograph fishes or other objects beneath it. This may, indeed, sometimes be done, but usually the attempt results in complete failure. The explanation is simple. At the moment of exposure the rays from the near submerged object are sharply focussed upon the plate. But at the same time more intense light from distant objects, out of focus, after being reflected from the water's surface reaches the plate also, which, when developed, consequently shows nothing. To set up an opaque screen shading the water's surface above the subject overcomes the difficulty. Through the shaded area, as through a window, one may photograph what lies below. However, the method is limited in its application. When the water exceeds 3ft. in depth it is usually better to use a submerged camera.
Dr. L. Boutan of Paris—pioneer in this field—between the years 1893 and 1898 attempted submarine photography at the Roscoff laboratory in Brittany with cameras of several sorts and appro priate and ingenious subsidiary apparatus. One of his cameras, made of metal, was directly submersible. Sea-water reached its interior, bathing both lens and plates. Although the result obtained was unsatisfactory because no thoroughly suitable lens was avail able, the principle seemed good to him. Other trials in which the camera was enclosed in and protected from the water by a metal box, through a glass window in which it looked out, were by com parison highly successful. This sort of apparatus, variously modified, has been used in all later work.
Boutan's cameras were of the simple detective type. Reighard, ten years after, at Tortugas, Fla., first used a reflecting camera protected in a water-tight box weighted down with lead till the window through which the camera looked was submerged, although the focussing hood remained above water and permitted him at all times to see what might be in the field. Excellent pictures were obtained within wading depth, beyond which he did not go.
Williamson Brothers, commercial motion photographers, prob ably as an independent invention, enclosed not only the camera, but the photographer as well, in a chamber suspended by a non collapsible open tube from a floating scow. Perfect pictures of the sea bottom and animals in shallow water were obtained in the clear water of the Bahamas, as the scow stood still or was towed slowly along. These writers must be credited with the first attempt to secure a photographic record in colour of submarine life in its natural setting. By using selective filters they secured films which when projected upon the screen gave an idea of the variety of colour upon a tropical reef, but since the yellows registered as reds the attempt can scarcely be considered entirely successful.
Longley, with Reighard's apparatus reduced to manageable size and improved, having recourse again to diving equipment as Boutan had done, gave the submarine camera greater mobility and a wider range of usefulness. It now lends itself to instantaneous or timed exposures of any ordinary subject at moderate depths. In the tropics, where sunlight is intense, snapshots, it is interest ing to note, may be taken as readily as upon land, but with some what longer exposure. Dr. Paul Bartsch, at Tortugas, and S. C. William Beebe, in Florida and the West Indies, have succeeded in obtaining pictures with a motion-picture camera similarly em ployed. Finally, Longley and Martin, working together and em ploying pound charges of flashlight powder set off electrically above water under a white cotton reflecting screen supported on pontoons by the same motion by which the submerged photog rapher exposed his plate, demonstrated the feasibility of submarine colour photography. The flash was so bright that even the slowly acting autochrome plate could be used for instantaneous exposures. Some results are shown in one of the plates under MARINE BIOLOGY.