Range finder

“ Range Finder and Predictor; Home and Distant Station Instruments. (See page 403.)
Continuous readings, by means of automatic indicators, of either the actual or the predicted ranges and azimuths of moving target at every instant and for any distance from 1,000 to 15,000 yards and through an azimuth of 160 degrees, are clearly presented at all times. The ranges are read in scales of 10-yard steps, and the azimuths for each .01 degree are traversed. ”

“ Well, that explains just how the range-finder works. The exact distance between the two men looking through the telescopes is known and fixed. Each man looks, as we have seen, at the same point out in the distance on the enemy's ship. That point is where the two unknown sides of the triangle come together. There is no time to figure the distance. A tenth of a second in these days is too much time to be lost. We must use electricity to do our figuring. ”

“ The position-finder can therefore, from a concealed and safe position, Coast Defence Instruments. automatically control the fire of a group of guns, whose detachments need not necessarily see the target engaged. As the observer follows the objective with the telescope of the instrument the range and bearing is simultaneously shown in the battery on convenient dials. The distance and direction thus communicated are the range and bearing from the guns, not as measured from the range-finder. The correction due to the displacement between gun and instrument is automatic. ”

“ Even a skillful range finder, if he is conscientious, can do no more than give a minimum and a maximum estimate of what he considers the range to be. The ranges must be communicated to the men accordingly. ”

“ Judging distance for the men as a formal practice is confined to ranges under 800 yards, but it does no harm to let them judge greater ranges. Let the unit commanders define targets to be fired at, omitting to state the range, and let the men [Pg 59] judge it for themselves and fire. Walk up the line and see that no man forgets to adjust his backsight for the distance he estimates. If possible, have the correct ranges taken previously with a range finder, and let the men know what they are after they have aimed. Each change of target gives the men a useful lesson in judging distance. ”

“ Nature has put our eyes so close together that the base is very short: and though it suffices for estimating the distance of a cigar tip, or of people in the same room, it is too short for telling us the distance of the enemy half-a-mile away. So the range-finder is made with a much longer base and the difficulty is largely reduced. But for greater distances still, such as that of the Moon, the range-finder becomes as useless as our eyes: the base is not nearly large enough. Instead of having our artificial eyes a few feet apart, we must put them miles apart ”

“ Probably the most wonderful of all these devices is the range-finder.
RANGE-FINDERS AT WORK ON THE ENEMY FROM THE FORE AND MAIN TOPS.
It isn't necessary for us to go deep into electrical science to understand how this instrument does its work. Electricity itself is a great mystery, and a puzzle in many ways to those who understand it best. Most of us have not been able to grasp its simpler puzzles until we studied them in college, and even then it would not be well for us to boast of what we knew. All we need to know, however, to understand the range-finder is a little problem in geometry. ”

“ The range-finder, which is a combination of a telescope and a spirit-level, requires not more than eight seconds to indicate the distance in yards on a scale, and the guns can then be brought to bear with unerring accuracy. Should the ship be hidden by smoke, observers with an electric position-finder are stationed some way off, and make known her movements by telegraph, whereby the gunners can keep up their fire although they cannot see the enemy. ”

“ By turning the elevation worm knob (c) , the images are lined up so that the same points will touch the dividing line. Now, by turning the measuring roller (M) on the right hand top side of the range finder, the upper image is shifted laterally until the same vertically disposed points of the target are exactly opposite each other. ”

“ Grenades should be thrown from mortars at an angle of 33°; otherwise they will be buried in the earth, and their fragments will not be sufficiently destructive. For tables of ranges, see Roberts’s “Hand-book of Artillery.”
Range, Point-blank. See Point-blank Range.
Range-finder. An instrument for determining ranges. There are several different principles which may be used. The distance may be measured, 1st, by the visual angle subtended by objects of known height; 2d, by the velocity of sound ”

“ Successful artillery practice therefore depends, in a great measure, upon the range-finder. The instrument used in harbour forts is known as the depression range-finder. As its name suggests, it solves a triangle in the vertical plane, of which the base is the height of the instrument above sea-level. Its appearance resembles some forms of theodolite (fig. 6) . A framework, capable of rotating in azimuth on a vertical ”

“ All long-range gunnery, whether on sea or on land, depends for success upon range-finding and the observation of fire, and as at sea the observations must be made from a point at which the gun is fired, the correction of fire becomes impossible if bad light or mist prevents the employment of observing glasses and range-finders. In the Jutland despatch particular attention was directed to the disadvantages we were under in the matter of range-finding from these causes. ”

“ But on land such big range-finders cannot conveniently173 be used; they are too bulky. When it is necessary to get the range of a very distant object, two observers are used who are stationed several hundred yards apart. These observers have telescopes which they bear upon the object, and the angle through which they have to turn the telescope is reported by telephone to the battery, where, by a rapid calculation, it is possible to estimate the exact position of the target. Then the gun is moved up or down, to the right or to the left, according to the calculation. ”

“ If the cover is good, the range-finders may next occupy the gun positions and proceed to take ranges. They must be most careful not to show themselves in the least and should work from cover to cover, some distance from the gun positions and not on the same alignment. ”

“ The tops are the places for the sharpshooters and the range-finders."
"The range-finders?"
"Exactly. You see, it is a difficult matter to get an exact range on an enemy several miles off, and we have to try to get the range in various ways. ”

“ Fig. 4.—Weldon rangefinder.
The merits of different field rangefinders depend mainly upon the balance of advantages they offer with respect to accuracy, suitability to variety of ground, simplicity, portability, and durability, these conditions being of a more or less conflicting character. The following are recognized principles: (1) the naked eye cannot with certainty appreciate less than one minute difference of angle, therefore telescopic power is necessary in proportion as the base is short compared with the range; (2) telescopes of high power cannot be steadied by hand alone ”

“ Rangefinders are, however, sometimes employed. The most worthy of notice is the Watkin depression rangefinder used by the British artillery in coast batteries. The instrument resembles in principle the Watkin field rangefinder, the height above the sea-level being a vertical base. The range is found by observing the angle of depression to the object. This is done by a powerful cross-wire telescope, which forms part of the instrument. The fastest steamer can be continuously followed, and even the successive grazes of shot and shell can be observed. ”

“ The measurement of ranges will commence the moment a firing-point has been chosen. Range-taking increases in importance rapidly with every 100 yards beyond 600 yards up to 2,000 yards, at which distance troops not in a close formation are only visible when in motion, or with a very favourable background or light. ”

“ A. Turn the pinion on the gun-arm to move the scale of the range correction-device until 2150 is set. (The zero of this scale = 2000.) (By doing this it is readily seen that the gun-arm range-scale is just 150 yards nearer the gun center; consequently all ranges read on this scale will be 150 yards more than if the range correction-device were at zero.) The azimuth correction is set by turning the micrometer until the number of even degrees of the azimuth correction (in this case one degree less) is read on the main scale, and the hundredths on the micrometer. ”

“ Observation of fire, when possible, is an effective means of ranging. If uncertainty exists as to elevation, it is better to underestimate than to overestimate the range. If it is necessary to fire at ranges beyond 1,000 yards, and observation is not possible, or the situation demands that some effect should be produced, quickly combined sights may be employed. ”

“ A position taken by bearings to buoys should not be considered a fix, but an estimated position (EP) , because buoys swing about their watch circle and may be out of position. Fix by Ranges: The navigator can plot a fix consisting of the intersection of two or more range arcs from charted objects. He can obtain an object’s range in several ways: Radar Ranges: See Figure 811b. The navigator may take ranges to two fixed objects. The intersection of the range arcs constitutes a fix. He can plot ranges from any point on the radar scope which he can correlate on his chart. ”

“ The selectmen usually walked the north lines only.
When the state domain, almost all dense forest, was first surveyed, the land was laid off in ranges, so-called, and tiers of lots. The various grants of land to persons for public services were also surveyed in a similar manner and the corners and lines established by means of stakes and stones, and of blazed trees. If a large rock happened to lie at the corner of a range or lot, the surveyor sometimes marked it with a drill. Such rocks made the best corners. ”

“ Where the base and the angles are variable. —The base angles are generally observed by instruments of the theodolite type, and the base is actually measured or found by means of a sub-base. The range is obtained by table or calculating scale. The Nolan rangefinder, which was the first telemeter used by the British artillery, was of this kind, (iii.) Where one base angle is a right angle, the other angles and base being variable. —The instrument used is generally double-reflecting of the sextant type,—the base being found as in (ii.) ”

“ Such ranges are of course entirely free from compass errors, and should be noted whenever there is favorable opportunity. The value of the range in plotting will increase with the distance between the objects, and if the two are close in proportion to the distance to the vessel the direction will be weak owing to the uncertainty in drawing a direction through close points. Artificial ranges are often erected as aids to navigation, usually to indicate the course to be followed in passing through a channel. ”

“ Rangefinders for Coast Batteries.—Rangefinding is less adapted to the requirements of coast defence than “position finding,”—a method which furnishes every gun with its proper training and elevation so that it can be fired without sighting the target. ”

“ There must be two sets of elevating gears, one which brings the axis of the gun and the sights together on to the target, thus finding the angle of sight and also pointing the axis of the gun at the target, and a second by which, independent of the sight which remains fixed, the elevation due to the range can be given to the gun and read by means of a pointer and dial marked in yards for range. ”

“ The angle available for subdivision, to measure ranges between infinity and 250 yds., is only one-third of a degree. In a travel of 6 in. the prism renders accurate measurements possible within the required limits. To bring images of distant objectives into coincidence, the prism must be moved towards the eye-piece, and for near objectives in the opposite direction. The range scale is attached to the prism. A consequent advantage is that the accuracy of the instrument is not affected by back lash arising from wear, or irregularity in the actuating mechanism. ”

“ After having marked four points on the board, showing the course of the target, place the prediction scale so that zero (0) is on the last point, or reading, and then mark off as many yards in advance of the last point as the first reads from zero. This point is known as the predicted point, and is used by the range officer only. As soon as the predicted point is found he sets his azimuth instrument at the given azimuth and when the target crosses the vertical wire in the instrument, he gives the signal "Fire." (See Fig. 82.)
[152]
GUN ARM FOR MORTARS.
Fig. 80.
[153]
Fig. ”

“ After passing standard tests in miniature range practice, and firing on the 30 yards range, every man should begin his practice on the open range confident in his own powers, and determined to prove his ability to hit. ”

“ Even for this there is a system of training, and men are instructed to consider how many times a hundred yards will fit into the space between them and the given object. They are taught how conditions of light and shade affect the apparent distance; how, with the sun shining from behind the observer on to the object, the distance appears less than when the sun is shining from behind the object on to the observer. They are taught at first to estimate short distances, and the range of objects chosen for experiment is gradually increased. In this, again, aptitude plays a considerable part ”