In the early days of steam navigation the Captain of a vessel could speak to the engineer through a tube and regulate the speed of the ship. When the vessels grew larger, the signalling was done by means of bells. That method is in common use to-day in many vessels that ply in harbors, such as river steamboats and tug-boats. As the ocean-liners increased in size the bell system of signalling became antiquated. The Captain or the navigator was 300 or 400 feet away from the engineer, and from 20 to 40 feet above the engine-room. In time of emergency it became necessary to send word to the engineer exactly what to do in half a dozen different cases. He must stop, back, go slow now with one engine and now with another, or with both. A long chain was run from a contrivance on the bridge to the engine-room. When the Captain pressed forward or backward a handle on a vertical dial, a handle in the engine-room would move on a similar dial, and a bell would ring to call attention to it, and the engineer knew at once what to do. This system is in use at the present time on all large passenger-ships and most war-ships in the world. Electricity has invaded this field also, and on the newer war-ships of the navy we have the signalling done by this agent. By the electric-engine telegraph, which Lieutenant Fiske of our navy has invented, not only does the engineer know at once when to go at full speed, half-speed, when to stop and back, and all that, but the Captain can tell at an instant, by looking at a little dial attached to his signalling apparatus, whether his orders have been understood. The little dial is connected with that part of the signalling apparatus in the engine-room on the same electric circuit, and thus the Captain knows exactly what is going on in the engine-room. But the new invention goes farther than that. It tells the engineer just how many revolutions of the screws a minute the Captain desires the engines to make. Full speed, for example, in the old way of signalling may mean anywhere from 80 to 90 or 100 revolutions of the screws. Half-speed may mean anywhere from 60 to 80 revolutions. The engineer in those cases has to use his own judgment as to what speed to employ, unless a message is sent especially to him from the Captain. In the electric device which we are just beginning to use there are certain notches on the dials, and the Captain can signal exactly the number of revolutions he desires each engine to make. He not only gets a signal back, but he has a telltale instrument before his eyes which shows that the engines are making 59, or 73, or whatever number of turns the Captain wishes them to make.