The daily morning journal and courier., 1898-02-21
HOW BIG GUNS ARE AIMED.
The Range-Finder Used on Seacoas
 Defences and Battle Ships.

The Range Finder Used on Seacoast
 Defences and Battle Ships.
 In reply to an inquiry from James Thompson, of Chicago, would say that the range-finder used on our seacoast defences is not Government secret, but is a patented appliance, an i'm provement upon a system that has been in use since ancient times. There are in use three sets of apparatus some what different from each other,} which were invented by Captain Watkins, an English engineer; Lieutenant Fisk, of our Navy. They are very complicated, and it is difficult to explain their oper- ation so it can be understood by lay men. All such inventions are an appli- ance of the mathematical principle that, knowing the base of triangle and the two angles at it's extremities, one can calculate the distance between them. On coast defences the base of the triangle Is permanent, with fixed objects to mark it's terminus. The an- gles are ascertained by observations through instruments made for that purpose, and when they are known there is series of printed calculations covering alll possible situations which enables the gunner to catch the dis- tance of his target at a glance.
 At sea, when a vessel is moving. the base is fixed and measured upon the deck. A telescope is placed at either end of that line, and the lenses of both are focused upon the object to be shot at. An observation Is then taken, a rapid mathematical calculation Is made, the book of tables is referred to, and in moment the gunner may know whether the enemy's cruiser is five and one-half or six and one fourth miles away, or any other given distance. This, of course, requires great deal of technical skill and mathematical abil- | ity, but 1t is said to be absolutely ac- curate, and the apparatus is so sensi- | tive and regulated to such fine de- gree that by turning a key monster gun weighing a hundred tons can be | instantly adjusted so that with given l quantity of powder 1t will carry pro- | jectile of a given weight exactly the distance which the range-finder has de- | termined. Of course, the gunner must know the contents of his cartridge, be- cause that is a material factor in his l problem. He must also make allow
 ances for the wind, for the resistance | of the atmosphere, for the curvature of | the earth and for the movement of the enemy's fleet if 1t is in motion. The
 range-dnder is. however, 8 great deal
 more accurate than the human eye and
 persons with defective vision will often
 insist that a gun is badly aimed and
 find out to the contrary after the shot
 is fired.
 Although we have guns on our battle-
 ships and in the Actresses on the coast
 that will carry a projectile thirteen
 miles 1t would be folly to attempt to
 use them at that distance, because, owing to the curvature of the earth, 1t
 would be impossible to see the target.
 A man in a small boat upon the surface
 of the water cannot see more than
 four miles. From the bridge of an or
 dinary man-of-war, which may be thir- | ty feet from the water, man with | good eyesight or with glass can see eight or nine miles. A man at the 1 masthead can see ten or twelve miles,
 but very indistinctly, and that is the limit of human vision on a level sur | face.-W. E. Curtis in The Chicago Record.