=Sound Detectors.=--We have heard many claims put forth concerning the great results which were to be attained in fighting the U-boat by the use of various sound-receiving devices in the nature of microphones, in detecting the presence of submarines by hearing the hum of the motors and the noise of their machinery. These devices are proposed both for offensive and defensive purposes. A vessel equipped with such mechanism is believed to be able to escape upon hearing a U-boat, or to seek out the submarine and destroy it. Those who have been expecting so much from this source are probably not aware of the fact that submarine inventors themselves were the first to utilize this method of sound detection under water to enable them to apprehend the presence of other vessels in their vicinity before coming to the surface; they have made use of such devices for years. I well remember my first long submergence of ten hours' duration down at Hampton Roads, near the mouth of the Chesapeake Bay, July 28, 1898. During this period of submergence the machinery was shut down for a time, and one of the first sensations we experienced was the strange sounds which came to us of the propellers and paddle-wheels of surface vessels passing in our vicinity. The first vessel that we heard was a tugboat; we could tell that by the sound of her puffing exhaust and the characteristic sound of her machinery. We thought at first she was coming right over where we were submerged, and feared she might carry away our masts, which extended above the surface, but she passed on, and then we heard coming at a distance the uneven and characteristic sound of a paddle-wheel steamer as her paddles slapped the surface of the water. Then we heard the slow, heavy pound of an ocean liner coming in, and knew that she had a loose crank-pin or cross-head bearing by the pound every time the crank-pin passed over the dead centre of its shaft. The click, click of the little high-speed launch was also easily detected--all this without any sound receiver on the vessel. Any of us simply sitting or standing anywhere in the submarine could hear outside sounds. By putting the head of an iron bolt against the skin of the ship and sticking the end of the bolt in my ear the sound was much intensified, as the whole steel fabric of the ship became a great sound collector. This led me to make experiments toward determining the direction of the sounds under water, and I applied for a patent on a device which could be swung in different directions, on the theory that the sound waves would be stronger when coming straight from their source, but shortly after this the experiments of Professor Gray and Messrs. Munday and Millett were published and I dropped my application and did nothing further in the matter, as they seemed to have solved the question in a satisfactory manner. Afterward Professor Fessenden brought out his oscillator and improved sound detector, with which it