As used in surveying, for example, where the base-line may be anything, according to circumstances, and the angles may likewise vary at both ends, elaborate trigonometrical calculations have to be performed to arrive at the desired result. If, however, the base-line be always the same, and one of the angles be always a right angle, the distance of the distant object will vary with the remaining angle. Indeed the scale by which that angle is measured can be made to give not degrees, but the distance of the object. Portable range-finders, therefore, in many cases have one reflector set for a right angle and only one of the reflectors movable. The instrument then shows the distance of the object at a glance. This is impossible in the case of two separate observations on a ship. In that case the base is always the same, but since the ship cannot be set at right angles to the object whenever a range has to be found, both angles have to be measured. There is, however, a beautifully simple little mechanism in which two pointers are set one to each of the two angles, and the distance is then shown instantly. APPENDIX A DESCRIPTION OF THE RIFLES SHOWN AT PAGE 240 THE GERMAN MAUSER can fire forty rounds a minute--more than any other rifle used in the war. The rifle is of the 1898 pattern, weighs 9 lb. 14 oz. with bayonet fixed, and is sighted from 219 to 2187 yards. The magazine holds five cartridges, packed in chargers. As the rifle is not provided with a cut-off, it cannot be used as a single-loader. With its long barrel and long bayonet it gives a stabbing length of 5 ft. 9 in.--8 in. longer than the British. THE AUSTRIAN RIFLE is the Mannlicher. This rifle is very fast in action as a snap back and forth of the wrist is sufficient to operate it. It is, however, more trying for prolonged work, owing to the throwing of the strain only on the wrist. Without the bayonet the rifle weighs only 8 lb. 5 oz., the lightest of all, yet the bullet--244 grains--is the heaviest used by any of the belligerents. The rifle is sighted from 410 to 2132 yards, and the barrel has a four-groove rifling. THE BRITISH LEE-ENFIELD--MARK III--is the outcome of the South African War. It is not too long for horseback and is yet quite efficient for infantry. The barrel is 25 in. long and has five grooves in the rifling. It is sighted from 200 to 2800 yards. The rifle is fitted with a magazine which holds ten cartridges packed in chargers, each of which contains five rounds, so that the magazine is filled with ten rounds in two motions. The rifle is also fitted with a cut-off, which enables it to be used as a single-loader. It is altogether a most efficient weapon.