Then there are important new devices which we can only mention. One of them is the sounding apparatus, by which the depth of water can be taken when going at full speed. The pressure of water on a column of air varies at certain depths of the ocean. This pressure is marked by the discoloration of a fluid in a tube through the agency of the salt water. The electric firing of guns is also interesting. A current of electricity is passed through a filament, such as we see in the incandescent lamp of a house electric light, and at once the heat sets the gun off as effectively as if a spark had ignited the powder. Then there is the aerophone, or fog-indicator, which points out the exact direction of some noise-making object by cutting the sound-wave in two, so as to send it first in one ear and then the other of the man who operates the invention, until finally he gets it in equal volume in both ears, and the dial on the machine points straight to the object which cannot be seen. All these inventions, which of themselves seem mere trifles, are necessary in these days, because of the wonderful advance in warfare and the construction of ships. In the old days the Captain could roar his orders out and make himself heard almost everywhere. Nowadays a fraction of a second may determine the outcome of a battle. He must be able to find the distance of his enemy, must fire his guns without aiming them in the old way, must regulate the speed of his ship to the single turn of a screw, must put his own helm at a certain angle to a degree. Without electricity he would be helpless in the noise and confusion. Even with electricity he is hampered, and so we may expect that the invention of these little devices will go on, until one man in a ship may control that engine of war as completely as if he were in every vital place in the ship at one and the same time. HOW TO USE THE VOICE. BY FELIX BEAUMONT.