A sweep line extending between the two submarines running parallel courses locates any intervening obstructions. (See text.)
As it is of historical value to record some of their experiences, I quote from Mr. Ernest Williamson's notes:
"During the first experiments in Hampton Roads, I found the condition of the water to be such that objects could be seen clearly for a distance of about six feet, and the photographic results showed that the fish and other objects photographed clearly at about four feet through the water. My theory, judging from the experiments, was that it would be possible to photograph through the water at almost the distance you could see clearly with the eye, and if it were possible to see through the water a distance of one hundred feet or more, as we were informed could be done in the West Indies, I reasoned that we could possibly get good photographic results at a distance of seventy-five feet.
"The latter proved to be correct, although in the middle of the experimental work I was a little bit concerned about a published record at that time of the experiments made by a Dr. Francis Ward in England. This Doctor Ward had built a cement well in the edge of a pond in his estate, and through a plate-glass window in the side of this well, under water, he had photographed fish and water-fowl. The Illustrated London News devoted four or five pages to his photographs and technical description of his work, and he made a point, in drawing his conclusions, that he believed that under the most favorable conditions it would be possible to photograph through water at a distance not exceeding three feet. None of his photographs showed any more than this, and he seemed to have technical reasons for believing that three feet was the limit.
"During the extensive work we have carried on in the West Indies, making scenes for our various productions, I have been down in the operating chamber at the base of the Williamson tube, when the water was so clear at times I have seen objects at a distance of two hundred feet—possibly more. At such times we have made motion pictures showing objects clearly at a distance of one hundred and fifty feet. These results were obtained at a depth of thirty feet. I have been down sixty feet in the chamber, and, of course, the greater the depth the less the sunlight under water and naturally the photographic results are not so good, but with the banks of Cooper-Hewitt lamps, which I successfully encased in watertight containers for the purpose of illuminating the under-sea, we obtained excellent results within a radius of the greater volume of this artificial light.
"For exploration and scientific work the artificial lights are a valuable adjunct, as they make it possible to photograph at any depth and at any time; but, there being so many other details to be taken care of in the taking of a scene under water, we try to do them all in the daytime. With as many as five divers operating in a scene, the divers wearing self-contained suits with no connection with the surface, having the tide and wind and the photographic apparatus and other things to be all worked at the same time, it is better to be working in the daylight, when you can keep your eye on the sharks and take care of the divers."
The reproduction of under-sea photographs shown in this book will give the reader some intimation of the "wonders of the deep," but unfortunately the wonderful colors and the play of light and movement cannot be reproduced.
Similarly, for scientific purposes as well as those of safeguarding navigation, submarines equipped for hydrographic work will prove of immense value. My work with submarine boats, both in the United States and foreign countries, has taught me that most charts are very unreliable, so far as their recorded depths are concerned. While they may be fairly accurate as to the average depths, they do not record many of the peaks or depressions that exist, especially where the water-bed is formed over a rock foundation. Silt and sand may fill in the depressions between peaks so that the average depth is fairly constant, yet here and there are outcropping peaks or humps that have, in many instances, proved fatal to shipping.