And first it may be stated that the _range-finder_ is largely a measure of mere economy. A two-million-dollar cruiser is not sailed, or lost, as a mere pastime. Whoever aims best will win the fight. Ten years ago the way of finding distance, or range, which is the same thing, was experimental. If a costly shot was fired over the enemy the next one was fired lower, and possibly between the two the range might be got, both vessels meantime changing positions and range. To change this, to either injure an antagonist quickly or get away, the "range-finder" was invented, as a matter not of business profit, by Lieutenant Bradley A. Fiske, of the U. S. Navy, in 1889. It has its reason in the familiar mathematical proposition that if two angles and one side of a triangle are known, the other sides of the triangle are easily found. That is, that it can be determined how far it is to a distant object without going to it. But Fiske's range-finder makes no mathematical calculations, nor requires them to be made, and is automatic. A base line permanently fixed on the ship is the one side of a triangle required. The distance of the object to be hit is determined by its being the apex of an imaginary triangle, and at each of the other angles, at the two ends of the base line, is fixed a spyglass. These are directed at the object. So far electricity has had nothing to do with the arrangement, but now it enters as the factor without which the device could have no adaptation. As the telescopes are turned to bear upon the target they move upon slides or wires bent into an arc, and these carry an electric current. The difference in length of the slide passed over in turning the telescopes upon the object causes a greater or less resistance to the current, precisely as a short wire carries a current more easily; with less "resistance;" than a long one. A contrivance for measuring the current, amounting to the same thing that other instruments do of the same class that are used every day, allows of this resistance being measured and read, not now in units of electricity, but _in distance to the apex of the triangle where the target is_; in yards. The man at each telescope has only to keep it pointed at the target as it moves, or as the vessel moves which wishes to hit it. And now even the telephone enters into the arrangement. Elsewhere in the ship another man may stand with the transmitter at his ear. He will hear a buzzing sound until the telescopes stop moving, and at the same time there will be under his eye a pointer moving over a graduated scale. The instant the sound ceases he reads the range denoted by the index and scale. The information is then conveyed in any desired way to the men at the guns; these, of course, being aimed by a scale corresponding to that under the eye of the man at the telephone. The plan is not here detailed as technical information valuable to the casual reader, but as showing the