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CHRONOGRAPHS two wires were taken, one of which came to the contact piece of drum, divided on its edge so that when a vernier is used a minute the target, and the other to the opposite extremity of the wire of angle may be read, is rotated rapidly by a motor at a practically across the mouth of the gun. Before the firing of the gun a con- uniform speed. The points of a row of steel-pointed pins, screwed inch' of- the tinuous circuit existed, including the gun wire ; when the target into a frame of ebonite, can be brought within surface of the drum. Each pin is a part of the secondary circuit was struck the second circuit was completed ; hut during the passage of the projectile both circuits were interrupted, and the of an induction coil, the space between the pins and the drum forming spark gaps. The drum is rubbed over with a weak solution duration of this interruption was indicated by the chronoscope. Professor Henry [Journal Franklin Inst., 1886) employed a of paraffin wax in benzol, which causes the markings produced by cylinder driven by clockwork, making ten revolutions per second. the sparks to be well defined. The records are read by means of The surface was divided into 100 equal parts, each equal to ^Vo- a fine hair stretched along the drum and just clear of it, the dots second. The time marks were made by two galvanometer needles, being located under the hair by means of a lens. The velocity of when successive screens were broken by a shot. Henry also used rotation is found by obtaining spark marks, due to the primary an induction-coil spark to mark the cylinder, the primary of the circuits of two induction coils being successively broken by a coil being in circuit with a battery and screen. This form of weight falling and knocking over two light levers. The distance chronograph is in many respects similar to the instrument of between the levers is about 3’77 inch, and the time of fall between Konstantinoff, which was constructed by Breguet and has been the levers is 0-018948 sec. In practice two drop weights are used, sometimes attributed to him (ies Comptes liendus, 1845). This to avoid the chance of an experiment being wasted. This chronochronograph consisted of a cylinder 1 m. in circumference and graph has been used for finding the velocity of projectiles after 0-36 m. long, driven by clockwork, the rotation being regulated by leaving the gun, and also for finding the rate at which a shot a governor provided with wings. A small carriage geared to the traverses the bore. For the latter purpose the shot successively wheelwork traversed its length, carrying electromagnetic signals. cuts insulated wires fixed in plugs screwed into the gun at known The electric chronograph signal usually consists of a small arma- intervals ; each wire forms a part of the primary of an induction ture (furnished with a style which marks a moving surface) moving coil, and as each is cut a dot is made on the rotating drum by the in front of an electromagnet, the armature being suddenly pulled induced spark. Jervis-Smith’s tram chronograph was devised for measuring periods off the poles of the electromagnet by a spring when the circuit is broken (Journal of Physiology, vol. ix. p. 408). The signals in of time varying from about one-fourth to one twenty-thousandth Breguet’s instrument were in a circuit, including the screens and part of a second (Proc. Boy. Soc. vol. xlv. p. 452. Improved batteries of a gun range. The measurement of time depended on from Pat. 1894. The Tram Chronograph, by F. J. Jervis-Smith, the regularity of rotation of the cylinder, on which each mm. F.R.S.). It consists of a metal girder having a T-shaped end. This carries two parallel steel rails, the edges of which lie in the same represented r^Vo second. In the Navez chronograph (1848) the time period is found by vertical plane. The girder is supported at its end, and at the means of a pendulum held at a large angle from the vertical by an extremities of the T-piece, on the Y-groove, trihedral hole, and electromagnet, which is in circuit with a screen on the gun range. plane system. A carriage or tram furnished with three grooved When the shot cuts this screen, the circuit is broken and the wheels runs on the rails, and a slightly - smoked glass plate is pendulum liberated and set swinging. When the next screen on attached to its vertical side. The tram in the original instrument the range is broken by the shot, the position of the pendulum is was propelled by a falling weight, but in an improved form one recorded and the distance it has passed through measured on a or more spiral springs are employed. All time traces are made divided arc. From this the time of traversing the space between immediately after the propelling force has ceased to act. _ The the screens is deduced. By means of an instrument known as a tram is brought to rest by a gradually applied brake, consisting disjunctor (Kncy. Brit. vol. xi. p. 300) the instrumental time-loss of two crossed leather bands stretched by two springs ; a projecor latency of the chronograph is determined. In Benton’s chrono- tion from the tram runs between the bands, and brings R to rest graph (1859) two pendulums are liberated, in the same manner as with but little lateral pressure. When, for certain physiological in the instrument of Navez, one on the cutting of the first screen, experiments, a low velocity of traverse is required, a heavy flythe other on the cutting of the second. The difference between wheel is mounted on the tram and geared to its wheels. . A pillar the swings of the two pendulums gives the time period sought for. also mounted on the hole, groove and plane method, is placed The disjunctor is also used in connexion with this. instrument. vertically in front of the glass, to carry the electromagnetic signals, In Vignotti’s chronograph (1857) again a pendulum is employed, which can be brought into contact with the glass by means of a furnished with a metal point, which moves close to paper impreg- tangent-screw. A standard fork by Koenig fixed to a pillar also nated with ferro-cyanide of potassium. The gun-range screens makes a trace on the glass, being automatically thrown into are included in the primary circuits of induction coils ; when these vibration. Tuning - forks may be calibrated by obtaining two circuits are broken a spark from the pointer marks the paper. signal markings on the plate, controlled by a standard clock of From these marks the time of traverse of the shot between the known rate. Two motions of a slide on the pillar, viz., of rotation and translation, allow a number of observations to be made.. The screens is determined. Colonel Sebert (Extraits du Memorial de VArtillerie de la Marine) traces are counted out on a sloping glass desk, and the time of devised a chronograph to indicate graphically the motion of recoil flight of a projectile between two or more screens is found. When of a cannon when fired. A pillar fixed to the ground at the side very close readings are required, they are made by means of a of the gun-carriage supported a tuning-fork, the vibration of traversing micrometer microscope. If the instrument is used for which was maintained electrically. The fork was provided with gun work, the tram is driven at full speed; when the distance a tracing point attached to one of the prongs, and so adjusted that between the screens is known, and also the time of flight, the it drew its path on a polished sheet of smoke - blackened metal midpoint velocity is found Toy applying Bashforth’s formula. attached to the gun-carriage, which traversed past the tracing When the velocity of shot from a shot-gun has to be found, a thin point, when the gun ran back. The fork used made 500 com- wire stretched across the muzzle takes the place of the first screen, plete vibrations per second. A central line was drawn through and a thin sheet of metal or cardboard carrying an electric conthe curved path of the tracing point, and every entire vibration tact, or a Branly coherer, takes the place of the second screen. cut the straight line twice, the interval between each intersection The electric firing circuit is provided with a safety key attached equalling -nVr second. The diagram so produced gave the total by a cord to the man who loads the gun and prepares the electric time of the accelerated motion of recoil of the gun, the maximum fuse, thus preventing him from getting into the line of fire when velocity of recoil, and the rate of acceleration of recoil from the the gun is fired by the chronograph. (Pat. Becord, 1897.) The beginning to the end of the motion. By means of an instrument tram, when the instrument is adjusted, has a practically constant furnished with a microscope and micrometers, the length and velocity of traverse. The polarizing photo-chronograph, designed and used by Dr A. amplitude, and the angle at which the curved line cut the central line, were measured. At each intersection (according to the in- Cushing Crehore and Dr G. Owen Squier at the United States ventor) the velocity could be deduced. The motion at any inter- Artillery School (Journal United States Artillery, 1895, vol. vi. section being compounded of the greatest velocity of the fork, p. 271), depends for its indications upon the rotation of a beam of while passing through the midpoint of the vibration and the light by a magnetic field, produced by a solenoidal current, which opened and closed by the passage of the projectile. The general velocity of recoil, the tangent made by the curve with the straight is is as follows :—A beam of light from an electric lamp line represents the ratio of the velocity of the fork to the velocity arrangement a lens, then a Nicol prism, next a glass cylinder furnished of recoil. If a be the amplitude of vibration, considered constant, traverses plane glass ends and coiled with insulated wire, then an v the velocity of the fork at the midpoint of its path, r the with velocity of recoil, a the angle made by the tangent to the curve analyser and two lenses, finally impinging on a photographic plate which rotation is given by an electric motor, the plane of with the straight line at the point of intersection, and t the line to rotation being perpendicular to the direction of the beam of light. of a complete vibration ; then, The same plate also records the shadow of a pierced projection attached to a tuning-fork, light^from the electric lamp being diverted by a mirror for this purpose. The solenoid used to proa magnetic field across the glass cylinder, which is filled with In Colonel Watkin’s chronograph (“Chronographs and their duce Application to Gun Ballistics,” Pros. Boy. Inst., 1896) a metal carbon bisulphide, is in circuit with a dynamo, resistances, and