The age-herald., 1898-05-14
sHARPsHOOTING AT SEA.
How Accuracy of Gun Firing Is Secured by
 the Use of the Range-Finder.

From the Scientific American.
 The accuracy of modern Iifled guns is one of the wonders of engineering. Two experimental shots fired few Gears ago al the same elevation from the same qua fell within thirty yards of each other, after tra- yersing a distance of twelve miles. If a modern rife Is laid upon the target with proper elevation and allowanc for windage, it Is safe to say the shot will find the mark. The correct elevation of the gun can only be determined if the distance of the target is known, and the exact detrmi1ation Of the distance of a moving object is prob- lem that has worried the gunner ever since the day when round shot was first thrown from the sides of the wooden tighuns ship
 In the early days the determination of the range was matter of guesswork. The gunner assumed a distance, elevated his gun accordingly and watched the course of the shot If it fell short he increased the elevation and if it passed over he decreased it. This was all very well in day when the guns were too feeble to do much exc cution, except at close range, and lew dozen shots thrown away made little lm- pression upon ships magazines. With the advent of modern ordnance, however, with it's 60-ton guns and costly charges, the necessity of accurate fire became impera- tive and ordnance experts set about de- vising some scientific method of finding the range at sea. The earliest and best known device of the kind was the inven- ton of Lieutenant Fiske, of the United States navy, which has been installed on many of our ships and is widely in use in the various naves of the world.
 The Fiske range-finder is based upon the well-known princiules of land surveying with the transit and engineers chain. If a surveying party come to broad river whose width has to be determined, base line is measured along the bank, and the angles which this line makes with mark on the opposite bank are measured by the transit. Then, knowing the length of the base line and the two angles, the distance across the river can be determined by trig- onometry
 Applying this to the range-inder, base line is carefully measured between two points near opposite ends of the ship. and over each point range-finder, answering to the engineers transit is permanently set up. If the telescopes of the two find- CTS are simultaneously converged upon the same point on a distant object (ship, for tress or city), the observers will be in pos session of the trigonometrical data neccs- sary to compute the distance, namely, the base and the two base angles.
 In the din. hurry and slaughter of sea fight, however, it would be difficult to make the necessary calculations. as the distance between the ships, and therefore the ob- served angles keep changing, and in order to make the determination of the distance automatic, Lieutenant F'iske placed his telescope in the circuit Of Wheatstone bridge and caused their change of position to record the distance of the object on the graduated scale of delicate galvanometer. All that was now necessary was for the observers at the two range-finders to keep the cross-hairs of the telescope upon the same point of the ship, and the electric cur rent translated Gas it were) the angles into distances and recorded them by the move ments of a needle over an arc graduated into hundreds and thousands of yards. One of these galvanometers is placed in the coming tower and one at each of the prin- cipal gun stations.