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CHRONOGRAPH

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Originally appearing in Volume V06, Page 305 of the 1911 Encyclopedia Britannica.
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CHRONOGRAPH from Gr. xp6vos, See also:

time, and ypit iEIV, to write). See also:Instruments whereby periods of time are measured and recorded are commonly called chronographs, but it would be more correct to give the name to the records produced. Instruments such as " stop watches " (see See also:WATCH), by means of which the time between events is shown on a See also:dial, are also called chronographs; they were originally rightly called chronoscopes (morals, to see). 4 The view that the chronicler invented such narratives is in-conceivable, and in the See also:present See also:stage of See also:historical See also:criticism is as unsound as an implicit reliance upon those See also:sources in the earlier books, which in their turn are often See also:long posterior to the events they See also:record. Although See also:Graf, in a See also:critical and exhaustive study (Geschichtlichen See also:Bucher See also:des A.T., See also:Leipzig, 1866), concluded that the See also:Chronicles have almost no value as a documentary source of the See also:ancient See also:history, he subsequently admitted in private See also:correspondence with Bertheau that this statement was too strong (See also:preface to Bertheau's Commentary, and ed., i873). Historical value. In the first experiments in See also:ballistics by B. See also:Robins, See also:Count See also:Rumford and See also:Charles See also:Hutton, the velocity of a projectile was found by means of the ballistic pendulum, in which the principle of momentum is applied in finding the velocity of a projectile (Principles of Gunnery, by See also:Benjamin Robins, edited by Hutton, 18o5, p. 84). It consisted of a pendulum of considerable See also:weight, which was displaced from its position of See also:rest by the impact of the See also:bullet, the velocity of which was required. A modification of the ballistic pendulum was also employed by W. E.

Metford (1824—1899) in his researches on different forms of rifling; the bob was made in the See also:

form of a long See also:cylinder, weighing about 140 lb, suspended with its See also:axis See also:horizontal from four wires at each end, all moving points being provided with See also:knife edges. The true length of suspension was deduced from observations of the time of a See also:complete small oscillation. The See also:head of the pendulum was furnished with a wooden See also:block, which caught the fragments of bullets fired at it, and its displacement was recorded by a See also:rod moved by the bob (The See also:Book of the See also:Rifle, by the Hon. T. F. See also:Fremantle, p. 336). An improved ballistic pendulum in which the geometric method of suspension is introduced has been used by A. See also:Mallock, to determine the resistance of the See also:air to bullets having a velocity up to 4500 F/S. (Prot. See also:Roy. See also:Soc., Nov.

1904). A ballistic pendulum, carried by a geometric suspension from five points, has also been employed by C. V. Boys in a See also:

research on the See also:elasticity of See also:golf balls, the displacement of the bob being recorded on a See also:sheet of smoked See also:glass.' For further See also:information on the See also:dynamics of the subject see See also:Text Book of Gunnery, 1897, p. 101. In nearly all forms of chronographs in which the ballistic pendulum method is not used, the beginning and end of a See also:period of time is recorded by means of some See also:kind of electrically See also:con-trolled mechanism; and in See also:order that small fractions of a second may be measured, tuning-forks are employed, giving any convenient number of vibrations per second, a See also:light See also:style or scribing point, usually of See also:aluminium, being attached to one of the legs of the tuning-See also:fork. A trace of the vibration is made on a See also:surface blackened with the See also:deposit from the See also:smoke of a See also:lamp. Glazed See also:paper is often employed when the velocity of the surface is slow, but when a high velocity of smoked surface is necessary, smoked glass offers far the least resistance to the See also:movement of the scribing points. If the surface be cylindrical, thin sheet See also:mica attached to it, and smoked, gives excellent results, and offers but little resistance to all the scribing points employed. The period of vibration of tuning-forks is determined by See also:direct or in-direct comparison with the mean See also:solar second, taken from a See also:standard See also:clock, the See also:rate of which is known from transit observations (" Recherches sur See also:les vibrations d'un See also:diapason etalon," R. Koenig, Wied. See also:Ann., 188o).

In the celebrated ballistic experiments of the Rev. F. Bashforth, the time markings were made electrically from a standard clock, and fractions of a second were estimated by See also:

interpolation. See also:Regnault (Memoires de 1'acad. des sciences, t. See also:xxxvii.) employed both a standard clock and a tuning-fork in his determination of the velocity of See also:sound. The effect of temperature on tuning-forks has been determined by 1 The velocity of the projectile is found thus. Let V be the velocity of the bob, due to the impact of the projectile, v the velocity of the projectile, h the height through which the bob is raised vertically, then wv=(W+w)V, and v= (w+1) Ogle If 1 be the true length of suspension. and C the length of the chord of the arc of displacement of the bob after being struck, then C2=2h1, and v= (w+1) \11.c. Also if T be the time of a complete small oscillation of the pendulum, 2r_ T so that 'es (w-W- +-1)2TCLord See also:Rayleigh and See also:Professor H. McLeod (Proc. Roy. Soc., 188o, 26, p. 162), who found the coefficient to be o•000rl per degree C. between 9° C. and 27° C. The beginning and end of a time period is marked on a moving surface in many ways.

Usually an electromagnetic stylus is employed, in which a scribing point suddenly moves when the electric See also:

circuit is broken by a projectile. Another method is to arrange the terminals of the secondary circuit of an See also:induction coil, so that when the See also:primary circuit is opened a small spark punctures or marks a moving surface (See also:Helmholtz, Phil. Mag., 1853, p. 6). A photographic See also:plate or film, moving in a dark chamber, is also used to receive markings produced by a See also:beam of light interrupted by a small See also:screen attached to an electromagnetic stylus, or by the legs of a tuning-fork, or by the See also:mercury See also:column of a capillary See also:electrometer. In certain researches on the explosive See also:wave of gases the light given by the burning gases made the time trace on a rapidly moving photographic film (H. B. See also:Dixon, Phil. Trans., 1903, 200, p. 323). In physiological chronography the stylus is in many cases actuated directly by the piece of muscle to which it is attached; when the muscle is stimulated its contraction moves the stylus on the moving surface of the myograph (M. See also:Foster, Text Book of See also:Physiology, 1879, p.

39). See also:

Gun Chronographs.—Probably the earliest forms of chronographs, not based on the ballistic pendulum method, are due to See also:Colonel Grobert, 1804, and Colonel Dabooz, 1818, both See also:officers trobert of the See also:French See also:army. In the See also:instrument by Grobert two acd large disks, attached to the same See also:axle 13 ft. apart, were Dabooz. rapidly rotated; the shot pierced each disk, the See also:angle between two holes giving the time of See also:flight of the See also:ball, when the angular velocity of the disks was known. In the instrument by Colonel Dabooz a See also:cord passing over two light pulleys, one See also:close to the gun, the other at a given distance from it, was stretched by a weight at the gun end and by a heavy screen at the other end. Behind this screen there was a fixed screen. The shot cut the cord and liberated the screen, which was perforated during its fall. The height of fall was measured by superposing the hole in the moving screen upon that in the fixed one. This gave the approximate time of flight of the shot over a given distance, and hence its velocity. In the See also:early form of chronoscope invented by See also:Sir C. See also:Wheatstone in 184o the period of time was measured by means of a See also:species of clock; driven by a weight; the dial pointer was started and hes stopped by the See also:action of an electromagnet which moved a stoneW. pawl engaging with a toothed See also:wheel fixed on the axle to which the dial pointer was attached. The instrument applied to the determination of the velocity of shot is described thus by See also:Wheat-See also:stone: " A wooden See also:ring embraced the mouth of the gun, and a See also:wire connected the opposite sides of the ring. At a proper distance the See also:target was erected, and so arranged that the least See also:motion given to it would establish a permanent contact between two See also:metal points.

One of the extremities of the wire of the electromagnet (before mentioned) was attached to one See also:

pole of a small See also:battery; to the other extremity of the electromagnet were attached two wires, one of which communicated with the contact piece of the target, and the other with one of the ends of the wire stretched across the mouth of the gun; from the other extremity of the voltaic battery two wires were taken, one of which came to the contact piece of the target, and the other to the opposite extremity of the wire across the mouth of the gun. Before the firing of the gun a continuous circuit existed, including the gun wire; when the target was struck the second circuit was completed; but during the passage of the projectile both circuits were interrupted, and the duration of this interruption was indicated by the chronoscope. ' Professor See also:Joseph See also:Henry (See also:Journal See also:Franklin Inst., 1886) employed a cylinder driven by clockwork, making ten revolutions per second. The surface was divided into 100 equal parts, each equal to Henyry. rti'aa second. The time marks were made by two galvano- See also:meter needles, when successive screens were broken by a shot. Henry also used an induction-coil spark to make the cylinder, the primary of the coil being in circuit with a battery and screen. This form of chronograph is in many respects similar to the instrument of Konstantinoff, which was constructed by L. F. C. Breguet and has been sometimes attributed to him (Comp/es rendus, 1845). This chronograph consisted of a cylinder 1 See also:metre in circumference and 0.36 metre longf driven by clockwork, the rotation being regulated by a See also:governor provided with wings. A small See also:carriage geared to the wheelwork traversed its length, carrying electromagnetic signals.

The electric chronograph See also:

signal usually consists of a small See also:armature (furnished with a style which marks a moving surface) moving in front of an electromagnet, the armature being suddenly pulled off the poles of the electromagnet by a See also:spring when the circuit is broken (Journal of Physiology, ix. 408). The signals in Breguet's instrument were in a circuit, including the screens and batteries of a gun range. The measurement of time depended on the h = VZ, and V =15gh. 2g If W be the weight of the bob, and w the weight of the projectile, then regularity of rotation of the cylinder, on which each mm., represented riaa second. In the chronograph of A. J. A. Navez (1848) the time period is found by means of a pendulum held at a large angle from the See also:vertical Navez. by an electromagnet, which is in circuit with a screen on the gun range. When the shot cuts this screen the circuit is broken and the pendulum liberated and set swinging. When the next screen on the range is broken by the shot, the position of the pendulum is recorded and the distance it has passed through measured on a divided arc. From this the time of traversing the space between the screens is deduced.

By means of an instrument known as a disjunctor the instrumental time-loss or latency of the chronograph See also:

Benton. is determined. In Benton's chronograph (1859) two pendulums are liberated, in the same manner as in the instrument of Navez, one on the cutting of the first screen, the other on the cutting of the second. The difference between the swings of the two pendulums gives the time period sought for. The disjunctor is also used in connexion with this instrument. In Vignotti's chronograph (1857) again a pendulum is employed, furnished with a metal point, which moves close to paper impregnated with ferrocyanide of See also:potassium. The gun-range screens are included in the primary circuits of induction coils; when these circuits are broken a spark from the pointer marks the paper. From these marks the time of See also:traverse of the shot between the screens is determined. In the Bashforth chronograph a See also:platform, arranged to descend slowly alongside of a vertical rotating cylinder, carries two markers, Bashforth, controlled by electromagnets, which describe a See also:double See also:spiral on the prepared surface of the cylinder. One electromagnet is in circuit with a clock, and the marker actuated by it marks seconds on the cylinder; the circuit of the other is completed through a See also:series of contact pieces attached to the screens through which the shot passes in See also:succession. On the gun range, when the shot reaches the first screen, it breaks a weighted See also:cotton See also:thread, which keeps a flexible wire in contact with a conductor. When the thread is broken by a shot, the wire leaves the conductor and almost immediately establishes the circuit through the next screen, by engaging with a second contact, the time of the rupture being recorded on the cylinder by the second marker. The velocity with which the cylinder rotates is such that the distance between successive clock marks indicating seconds is about 18 in.; hence the marks corresponding with the severance of a thread can be allotted their value in fractions of seconds with See also:great accuracy.

The times when the shot passes successive screens being thus recorded on the spiral described by the second marker, and the distance between each screen being known, the velocity of the shot can be calculated. The chronoscope invented by Sir See also:

Andrew See also:Noble is so well adapted to the measurement of very small intervals of time that it is usually Nobie. employed to ascertain the velocity acquired by a shot at different parts of the See also:bore in moving from a See also:state of rest inside the gun. A series of " cutting plugs " is screwed into the sides of the gun at measured intervals, and in each is inserted a See also:loop of wire which forms See also:part of the primary circuit of an induction coil. On the passage of a shot this wire is severed by means of a small knife which projects into the bore and is actuated by the shot as it passes; the circuit being thus broken, a spark passes between the terminals of the secondary of the coil. There is a See also:separate coil and circuit for each plug. The recording arrangement consists of a series of disks, one for each plug, mounted on one axle and rotating at a high angular velocity. The edges of these disks are covered with a coating of lamp-See also:black, and the secondaries of the coils are caused to See also:discharge against them, so that a See also:minute spot burnt in the lamp-black of each disk indicates the moment of the cutting of the wire in the corresponding plug. Hence measurement of the distance between two successive spots gives the time occupied by the shot in moving over the portion of the bore between two successive plugs. By the aid of a See also:vernier, readings are made to thousandths of an See also:inch, and the peripheral velocity of the disks being iioo in. a second, the See also:machine indicates portions of time rather less than one-millionth of a second ; it is, in fact, practically correct to See also:hundred-thousandths of a second (Phil. Trans., 1875, pt. i.). In the Le Boulenge chronograph (" Chronograph le Boulenge," See also:par M. Breger, See also:Commission de (-avre, See also:Sept.

1880) two screens are Le used. The wire of the first forms part of the circuit of an Boulenge. electromagnet which, so long as it is energized, supports a vertical rod called the " chronometer." Hence when the circuit is broken by the passage of a shot through the screen this rod drops. The wire of the second screen conveys a current through another electromagnet which supports a much shorter rod. This " registrar," as it is called, when released by the shot severing the wire of the second screen, falls on a disk which sets See also:

free a spring, and causes a horizontal knife to See also:fly forward and nick• a See also:zinc See also:tube with which the chronometer rod is sheathed. Hence the long rod will be falling for a certain time, while the shot is travelling between the two screens, before the See also:short rod is released; and the longer the shot takes to travel this distance, the farther the long rod falls, and the higher up on it will be the nick made by the knife. A See also:simple calculation connects the distance through which the rod falls with the time occupied by the shot in travelling over the distance between the screens, and thus its velocity ascertained. The nick made by the knife, if released while the chronometer rod is still suspended,is the zero point. If both rods are released simultaneously, as is done by breaking both circuits at once by means of a " disjunctor," a certain time is consumed by the short rod in reaching the disk, setting free the spring and cutting a nick in the zinc; and during this time the long rod is falling into a See also:recess in the stand deep enough to receive its full length. The instrument is so adjusted that the nick thus made is 4.435 rn. above the zero point, corresponding to 0.15 sec. This is the disjunctor See also:reading, and requires to be frequently corrected during experiments. The instrument was modified and improved by Colonel H. C.

See also:

Holden, F.R.S. For further information respecting formulae See also:relating to it see Text Book of Gunnery (1897). The electric chronograph of the See also:late H. S. S. See also:Watkin consists of two long cylinders rotating on vertical axes, and between them a cylindrical weight, having a pointed head, is free to fall. watidn. The weight is furnished with an insulated wire which passes through it at right angles to its longest axis. When the weight falls the ends of the insulated wire move very close to the surfaces of the cylinders which form part of a secondary circuit of an induction coil, the primary circuit of which is opened when a screen is ruptured by a shot. A minute See also:mark is made by the induced spark on the smoked paper with which the cylinders are covered. The time period between events is deduced from the space fallen through by the weight, and by means of a See also:scale, graduated for a given distance between the screens, the velocity of a shot is at once found. It may be noted that the method of See also:release is such that the falling weight is not subjected, after it has begun to fall, to a diminishing magnetic See also:field, which would be the See also:case if it were directly supported by an electromagnet. An See also:iron rod when falling from an electromagnet, during a minute portion of its fall, is subject to a diminishing force acting in the opposite sense to that of gravity, whereby its time of fall is slightly changed.

Colonel Sebert (.Extraits du memorial de l'artillerie de la marine) devised a chronograph to indicate graphically the motion of recoil of a See also:

cannon when fired. A See also:pillar fixed to the ground at sebert. the See also:side of the gun-carriage supported a tuning-fork, the vibration of which was maintained electrically. The fork was provided with a tracing point attached to one of the prongs, and so adjusted that it See also:drew its path on a polished sheet of smoke-blackened metal attached to the gun-carriage, which traversed past the tracing point when the gun ran back. The fork used made goo complete vibrations per second. A central See also:line was See also:drawn through the curved path of the tracing point, and every entire vibration cut the straight line twice, the See also:interval between each intersection equalling iaa second. The See also:diagram so produced gave the See also:total time of the accelerated motion of recoil of the gun, the maximum velocity of recoil, and the rate of See also:acceleration of recoil from the beginning to the end of the motion. By means of an instrument furnished with a micro-See also:scope and micrometers, the length and See also:amplitude, and the angle at which the curved line cut the central line, were measured. At each intersection (according to the inventor) the velocity could be deduced. The motion at any intersection being compounded of the greatest velocity of the fork, while passing through the midpoint of the vibration and the velocity of recoil, the tangent made by the See also:curve with the straight line represents the ratio of the velocity of the fork to the velocity of recoil. If a be the amplitude of vibration, considered See also:constant, v the velocity of the fork at the midpoint of its path, r the velocity of recoil, a the angle made by the tangent to the curve with the straight line at the point of intersection, and t the line of a complete vibration; then, v=2aa/t; r = v/tan a. F. Jervis-See also:Smith's tram chronograph (See also:Patents, 1894, 1897, 1903) was devised for measuring periods of time varying from about one- See also:fourth to one twenty-thousandth part of a second (Prot.

Jervis. Roy. Soc., 1889, 45, p. 452; The Tram Chronograph, by Smith. F. Jervis-Smith, F.R.S.). It consists of a metal girder having a T-shaped end. This carries two parallel See also:

steel rails, the edges of which See also:lie in the same vertical See also:plane. The girder, which is slightly inclined to the horizontal plane, is geometrically supported, being carried at its end, and at the extremities of the T-piece, on a V-groove, trihedral hole and plane. A carriage or tram furnished with three grooved wheels runs on the rails, and a slightly smoked glass plate is attached to its vertical side. The tram in the See also:original instrument was propelled by a falling weight, but in an improved form one or more spiral springs are employed. All time traces are made immediately after the propelling force has ceased to See also:act.

The tram is brought to rest by a gradually applied See also:

brake, consisting of two crossed See also:leather bands stretched by two springs; a See also:projection from the tram runs between the bands, and brings it to rest with but little lateral pressure. When, for certain physiological experiments, a See also:low velocity of traverse is required, a heavy fly-wheel is mounted on the tram and geared to its wheels. A pillar also mounted geometrically, placed vertically in front of the carriage, carries the electromagnet style or signals and tuning-fork which can be brought into contact with the glass by means of a See also:lever. Also styli are used which depend for their action on the displacement of one or more wires under tension or torsion carrying a current in a magnetic field, the See also:condition being such that no magnetic lag due to iron armatures and cores exists. Two motions of a slide on the pillar, viz. of rotation and See also:translation, allow a number of observations to be made. The traces are counted out on a sloping glass See also:desk, and the time of flight of a projectile between two or more screens is found. When very close readings are required, they are made by means of a traversing geometric See also:micrometer See also:microscope. When the distance between the screens is known, and also the time of flight, the See also:mid-point velocity is found by applying Bashforth's See also:formula. When the velocity of shot from a shot-gun has to be found, a thin wire stretched across the muzzle takes the See also:place of the first screen, and a thin sheet of metal or cardboard carrying an electric contact, or a Branly coherer, the conductivity of which is restored by means of an induced current, takes the place of the second screen. The electric firing circuit is provided with a safety See also:key attached by a cord to the See also:man who loads the gun and prepares the electric fuse. The firing circuit is closed by inserting the key in a switch at the See also:rear of the gun, thus preventing him from getting into the line of See also:fire when the gun is fired by the chronograph. The tram, when the instrument is adjusted, has a practically constant velocity of traverse.

The polarizing photo-chronograph, designed and used by A. C. Crehore and G. O. Squier at the See also:

United States See also:Artillery School Crehore- (Trans. Amer. Inst. Elect. Eng. vol. 14, and Journal Squler. United States Artillery, 1895, 6, p. 271), depends for its indications upon the rotation of a beam of light by a magnetic field, produced by a solenoidal current which is opened and closed by the passage of the projectile.

The See also:

general arrangement is as follows:—A beam of light from an electric lamp traverses a See also:lens, then a See also:Nicol See also:prism, next a glass cylinder furnished with plane glass ends and coiled with insulated wire, then an analyser and two lenses, finally impinging on a photographic plate to which rotation is given by an electric motor, the plane of rotation being perpendicular to the direction of the beam of light. The same plate also records the See also:shadow of a pierced projection attached to a tuning-fork, light from the electric lamp being diverted by a See also:mirror for this purpose. The solenoid used to produce a magnetic field across the glass cylinder, which is filled with See also:carbon bisulphide, is in circuit with a See also:dynamo, resistances, and the screens on the gun range. It is a well-known phenomenon in physics that when, with the above-mentioned See also:combination of polarizing Nicol prism and analyser, the light is shut off by rotating the analyser, it is instantly restored when the carbon bisulphide is placed in a magnetic field. This phenomenon is utilized in this instrument. The projectile, by cutting the wire screens, causes the magnetic field to cease and light to pass. By means of an automatic switch the projectile, after cutting a screen, restores the electric circuit, so that successive records are registered. After a record has been made it is read by means of a micrometer microscope, the angle moved through by the photographic disk is found, and hence the time period between two events. In the photo-chronograph described in Untersuchungen fiber See also:die Vibration des Gewehrlaufs, by C. See also:Crane and K. R. See also:Koch (See also:Munich, 1899), also See also:note on the same, Nature, 61, p.

58, a sensitive plate moving in a straight line receives the record of the movement of the barrels of firearms when discharged. It was mainly used to determine the " angle or See also:

error of departure " in ballistics. In a second chronograph by Watkin (" Chronographs and their Application to Gun Ballistics," Proc. Roy. Inst., 1896), a metal See also:drum, Weida. divided on its edge so that when a vernier is used a minute of angle may be read, is rotated rapidly by a motor at a practically See also:uniform See also:speed. The points of a See also:row of steel-pointed pins, screwed into a See also:frame of ebonite, can be brought within plc, in. of the surface of the drum. Each See also:pin is a part of the secondary circuit of an induction coil, the space between the pins and the drum forming spark-gaps. The drum is rubbed over with a weak See also:solution of See also:paraffin See also:wax in benzol, which causes the markings produced by the See also:sparks to be well defined. The records are read by means of a See also:fine See also:hair stretched along the drum and just clear of it, the dots being located under the hair by means of a lens. The velocity of rotation is found by obtaining spark marks, due to the primary circuits of two induction coils being successively broken by a weight falling and breaking the two electric circuits of the coils in succession at a known distance apart. This chronograph has been used for finding the velocity of projectiles after leaving the gun, and also for finding the rate at which a shot traverses the bore.

For the latter purpose the shot successively cuts insulated wires fixed in plugs screwed into the gun at known intervals; each wire forms a part of the primary of an induction coil, and as each is cut a dot is made on the rotating drum by the induced spark. In the chronograph of See also:

Marcel Deprez, a cylinder for receiving records is driven at a high velocity, 4 to 5 metres per second surface Deprez. velocity. The velocity is determined by means of an, electrically-driven tuning-fork, the traces being read by means of a vernier See also:gauge. A mercury speed See also:indicator of the Rams-bottom type enables the rotation to be continuously controlled (A. Favarger, L'Electriciti et. ses applications a la ctronomitrie). Astronomical Chronographs.—The astronomical chronograph is an instrument whereby an observer is enabled to See also:register the time Dent. of transit of a See also:star on a sheet of paper attached to a re- volving cylinder. A metal cylinder covered with a sheet of paper is rotated by clockwork controlled by a conical pendulum, or by a centrifugal clock governor such as is used for See also:driving a See also:telescope. By means of a See also:screw longer than the cylinder, mounted parallel with the axis of the cylinder and rotated by the clockwork, a carriage is made to traverse close to the paper. In some instruments this carriage is furnished with a metal point, and in others with a style-graphic See also:ink See also:pen. The point or pen is made to See also:touch the paper by an electromagnet, the electric current of which is closed by the observer at the transit instrument, and a mark is recorded on the revolving cylinder. The movement of the same point or pen is also controlled by a standard clock, so that at the end of each second a mark is made. The cylinder makes one revolution per minute, and the minute is indicated by the omission of the rnark.

In E. J. Dent's form (Nature, 23, p. 59) continuous observations can be recorded for 63 See also:

hours. The conical pendulum used to govern the rotation of the cylinder was the invention of Sir G. B. See also:Airy. The See also:lower end is geared to a metal plate which sweeps through an See also:annular trough filled with See also:glycerin and See also:water. When the path of the pendulum exceeds a certain See also:diameter it causes the plate to enter the liquid more deeply, its motion being thereby checked; also, when the pendulum moves in a smaller circle the plate is lifted out of the liquid and the resistance is diminished in the same proportion as the force. The compensatory action is considerable; doubling the driving See also:power produces no perceptible difference in the time. To prevent the injury of the conical pendulum and the wheel See also:work by any sudden check of the cylinder, a ratch-wheel connexion is placed between the cylinder and the See also:train of wheel work; this enables the pendulum to run on until it gradually comes to rest. The pendulum, which weighs about i81b, is compensated, and makes one revolution in two seconds; it is suspended from a See also:bracket by means of two flexible steel springs placed at right angles to one another.

The See also:

observatory of See also:Washburn, University of See also:Wisconsin, is furnished with a chronograph of the same type as that of Dent (See also:Annals Harvard See also:Coll. Obs. vol. i. pt. ii. p. 34), but in this instrument the rotation of the cylinder is controlled by a double conical pendulum governor of See also:peculiar construction. When the balls fly out beyond a certain point, one of them engages with a See also:hook attached to a See also:brass cylinder which embraces the vertical axle loosely. When this See also:mass is pulled aside the work done on it diminishes the speed of the governor. The pendulum ball usually strikes the hook from 6o to 7o times per minute. See also:Governors on this principle were adopted by Alvan See also:Clark for driving heliostats in the United States Transit of See also:Venus Expedition, 1874. In the astronomical chronograph designed by Sir See also:Howard Grubb (Proc. Inst. Mech. Eng., See also:July 1888), the recording cylinders—two in number—are driven by a weight acting on a train of wheel Grubb. work controlled by an astronomical telescope governor. The peculiar feature of this instrument is that the axle is geared to a See also:shaft which communicates motion to the cylinders through a mechanism whereby the speed of rotation is constantly corrected by a standard clock.

Should the rotation fall below the correct speed it is automatically accelerated, and if its speed of rotation rises above the correct one it is retarded. The accelerator and retarder are thrown into action by electromagnets, controlled by a " detector" mounted on the same shaft. The rather complicated mechanism employed to effect the correction is described and fully illustrated in the reference given. The cylinders are covered with paper, but all the markings are made with a stylographic pen. The marks indicating seconds are dots, but those made by the observer are short lines. When an observation is about to be made the observer first notes the See also:

hour and minute, and, by pressing a contact key attached to a flexible cord at the transit instrument, marks the paper with a See also:letter in See also:Morse See also:telegraph characters, indicating the hour and minute; he then See also:waits till a micrometer wire cuts a star and at the instant closes the circuit, so that the second and fraction of a second are registered on the chronograph paper. When a set of observations have been taken, the paper is removed from the cylinder, and the same results are obtained by applying a suitably divided See also:rule to the marked paper, fractions of a second being estimated by applying a piece of glass ruled with eleven straight lines converging to a point. The ends of these lines on the See also:base of the triangle so formed are equidistant on one edge of the glass, so that when the first and last lines are so placed as to coincide with the beginning and end of the markings of a second, that second is"divided into ten equal parts. The base of the triangle is always kept parallel with the line of dots. The papers, after they have been examined and the results registered, are kept for reference. In the astronomical chronograph of Hipp, used in determining longitudes, the movement of a recording cylinder is regulated by means of a toothed wheel, the last of a clockwork train, Hlpp controlled by a vibrating metal See also:tongue; this important feature is described in detail in Favarger's work cited above. Acoustic Chronographs.--In the chronograph devised by H.

V. Regnault (Acad. des Sc., 1868) to determine the velocity of sound propagated through a great length of See also:

pipe, a See also:band of Regnauit. paper 27 mm. wide was continuously unrolled from a bobbin by means of an electromagnetic See also:engine. In its passage over a See also:pulley it passed over a smoky lamp See also:flame, which covered it with a thin deposit of carbon. It next passed over a cylinder in contact with the style of a tuning-fork kept in vibration by electromagnets placed on either side of its prongs, the current being interrupted by the fork; it was also in contact with an electric signal controlled by a standard clock. Also an electromagnetic signal marked the beginning and end of a time period. Thus three markings were registered on the See also:hand, viz. the time of the pendulum, the vibrations of the fork, and the marking of the signal due to the opening and closing of the current by See also:electrical contacts attached to diaphragms on which the sound wave acted. The contacts consisted of minute hammers resting on metal points fixed to the centre of diaphragms which closed the end of the experimental pipes. The signal marked the instant at which a sound wave impinged on a See also:diaphragm. The markings on the paper band gave the period of time between two events, and the number of vibrations of the tuning-fork per second was estimated by means of markings due to the clock. The sound wave was usually originated by firing a See also:pistol into the pipe furnished with diaphragms and contact pieces. In the chronographic use of the Morse telegraph instrument (See also:Stewart and See also:Gee, Elementary See also:Practical Phys. p. 234) a circuit is See also:Ayrton arranged which includes a seconds' pendulum furnished and See also:Perry. with a fine See also:platinum wire below the bob, which sweeps through a small mass of mercury forming a part of the circuit.

There is a Morse key for closing the circuit. A fast-See also:

running Morse instrument and a battery are placed across this circuit as a shunt. A succession of dots is made on the paper ribbon by the circuit being closed by the pendulum, and the space between each adjacent dot indicates a period of one second's duration. Also, when the key is depressed, a mark is made on the paper. To measure a period of time, the key is depressed at the beginning and end of the period, causing two dots to be made on the ribbon; the interval between these, when measured by the intervals due to the pendulum, gives the length of the period in seconds, and also in fractions of a second, when the seconds' interval is subdivided into convenient equal parts. This apparatus has been used in determination of the velocity of sound. In the break circuit arrangement of pendulum key and Morse instrument the markings appear as breaks in a line which would other-See also:wise be continuous. This combination was employed by Professors W. E. Ayrton and J. Perry in their determination of the acceleration of gravity at Tokio, 1877–1878 (Prot. Phys.

Soc. Lond. 3, p. 268). In the tuning-fork electro-chronograph attributed to Hipp a metal cylinder covered with smoked glazed paper is rotated uniformly Hipp. by clockwork, a tuning-fork armed with a metallic style being so adjusted that it makes a clear fine line on the smoked paper. The tuning-fork is placed in the secondary circuit of an induction coil, so that when the primary circuit is broken an induced spark removes a speck of black from the paper and leaves a mark. The time period is deduced by counting the number of vibrations and fractions of vibration of the tuning-fork as recorded by a sinuous line on the cylinder. In later forms of this instrument the cylinder advances as it rotates, and a spiral line is traced. To obtain See also:

good results the spark must be very small, for when large it often leaps laterally from the end of the style, and does not give the true position of the style when the circuit is broken. The same arrangement of tuning-fork and revolving cylinder, with the addition See also:Mayer. of a standard clock, has been used by A. M. Mayer (Trans.

Nat. Acad. Sci. U.S.A. vol. iii.) and others for calibrating tuning-forks, and comparing their vibrations directly with the beats of the pendulum of a standard clock the rate of which is known. The pendulum marks and breaks the primary circuit by carrying a small platinum wire through a small mercury meniscus. Better and apparently certain contacts can be obtained from platinum contact-pieces, brought together above the pendulum by means of a toothed wheel on the scape-wheel arbor. Sparking at the contact points is greatly reduced by placing a couple of See also:

lead plates in dilute sulphuric See also:acid as a shunt across the battery circuit. For Physiological Purposes.—A. Fick's pendulum myograph or muscle-trace See also:recorder is described in Vierteljahrsschr. der naturforsch. Fick. Ges. in See also:Zurich, 1862, S. 307, and in Text-book of Physiology, M.

Foster, pp. 42, 45. It was used to obtain a record of the contraction of a muscle when stimulated. In many respects the instrument is similar to the electro-ballistic chronograph of Navez. A long pendulum, consisting of a braced metal frame, carries at its lower end a sheet of smoked glass. The pendulum swings about an axis supported by a See also:

wall bracket. Previous to an experiment, the pendulum is held on one side of its lowest position by a spring catch; when this is depressed it is free to See also:swing. At the end of its swing it engages with another spring catch. In front of the moving glass plate a tuning-fork is fixed, also a lever actuated by the muscle to be electrically stimulated. When the pendulum swings through its arc, it knocks over the contact key in the primary circuit of an induction coil, the secondary of which is in connexion with the muscle. The smoked plate receives the traces of the style of the tuning-fork and of the lever attached to the muscle, and also the trace of an electromagnetic signal which marks the instant at which the primary circuit is broken. After the traces are made, they are ruled through with radial lines, cutting the three traces, and the time intervals between different parts of the muscle curve are measured in terms of the period of vibration of the tuning-fork, as in other chronographs in which the tuning-fork is employed.

In the spring myograph of E. Du Bois Reymond (Munk's Physiologie des Menschen, p. 398) a smoked glass plate attached to a metal See also:

DuBois rod is shot by a spiral spring along two guides with a Ieymond. velocity which is not uniform. The traces of a style moved by the muscle under examination, and of a tuning-fork, are recorded on the glass plate, the shooter during its traverse knocking over one or more electric keys, which break the primary circuit of an induction coil, the induced current stimulating the muscle. In the photo-electric chronograph devised by G. J. Burch, F.R.S. (Journ. of Physiology, 18, p. 125 ; Electrician, 37 , p. 436) , the rapid movements of the column of mercury in a capillary electrometer Burch. used in physiological research are recorded on a sensitive plate moving at a uniform angular velocity. The trace of the vibrating prongs of a tuning-fork of known period is also recorded on the plate, the light used being that of the electric arc. The images of the meniscus of the mercury column and of the moving fork are focused on the plate by a lens.

Excellent results have been obtained with tilts instrument. An important development of a See also:

branch of chronography is due to E. J. Marey (Comples rendus, 7. aoi t 1882, and Le Mouvement, par E. J. Marey, See also:Paris, 1894), who employed a photographic Marey plate for receiving successive pictures of moving See also:objects, at definite times, when investigating the movements of animals, birds, fishes, See also:insects, and also microscopic objects such as vorticellae. The instrument in one of its forms consisted of a See also:camera and lens. In front of the sensitive plate and close to it a disk, pierced with radial slits, revolved at a given angular velocity, and each time a slit passed by the plate was exposed. But since, in the time of passage of the space between the slits, the See also:object had moved by a certain amount across the field of view, a fresh impression was produced at each exposure. The object, well illuminated by sunlight, moved in front of a black background. Since the angular velocity of the disk was known, and the number of slits, the time between the successive positions of the object was also known. Marey (La Mithode graphique, pp.

133, 142, 456), by means of pneumatic signals and a rotating cylinder covered with smoked glazed paper, measured the time of the movements of the limbs of animals. The instrument consists of a recording cylinder rotated at a uniform angular velocity by clockwork controlled by a See also:

fan governor, and pneumatic signal, constructed thus. One end of a closed shallow cylinder, about 4 cm. dia., is furnished with a stretched See also:rubber membrane. A light lever, moving about an axis near the edge of the cylinder, is attached to the centre of the membrane by a short rod, its free end moving as the membrane is distended. The cylinder is connected by a flexible tube with a similar cylinder and membrane, but without a lever, which is attached to that part of the See also:body of the See also:animal the movement of which is under investigation. The See also:system is full of air, so that when the membrane attached to the animal is compressed, the membrane which moves the lever is distended and the lever moved. Its end, which carries a scribing point, marks the smoked paper on the rotating cylinder. The pneumatic signal is called by Marey " See also:tambour a levier." References to Chronographic Methods:—(1) Chronographs used in Physiology: Helmholtz, " On Methods of measuring very small Portions of Time," Phil. Mag. (1853), 6; Id., Verhandlungen der f'hysikalisch-medicinischen Geselischaft in See also:Wurzburg (1872) ; See also:Harless, ` Das See also:Attwood'sche Myographion," Abhandlungen der k. bayerischen Akademie der Wissenschaften (1862); Id., Fall-Myographion aufgestellt in der Wiener Weltausstellung in der Abteilung See also:fur das Unterrichtswesen von Ungarn (See also:Budapest, 1873) ; Hensen, ` Myographion mit vibratorischer Bewegung," Arbeiten aus See also:dean Kieler physiol. Instil. (1868); Brflcke, Sitzungsber. d Wien.

Acad. (1877); Pfliiger. " Myographion ohne Bewegung," Untersuchungen iiber die Ph ysiologie des Electrotonus (1859) ; Pouillet, Compt. rend. (1844) ; I. Munk, Physiologie des Menschen (for Pfluger's cylinder governed by conical pendulum); J. G. M'Kendrick, See also:

Life in Motion (1892) (for early form of cylinder chronograph by See also:Thomas See also:Young) ; See also:Stirling, Outlines of Practical Physiology (for reaction-time chronographs of F. See also:Galton and Exner). (2) Chronographs used in gun work and for other purposes: See also:Sabine, Phil. Magi (1876); Moisson, See also:Notice sur la chronographic systeme See also:Schultz (Paris, 1875); See also:Paul la Cour, La Roue phonique (See also:Copenhagen. 1878) ; See also:Mach, " Collected Papers on Chronographs," Nature, 42, p. 250; C.

V. Boys, " Bullets photographed in Flight," Nature, 47, p. 415; Pneumatic Tube Co., Paris, " Chronograph," Nature, 9, p. 105; G. C. Foster, " Laboratory Chronograph," Nature, 13, p. 139; E. S. Holden, "Astronomical Chronograph," Nature, 26, p. 368; D'See also:

Arsonval, La Lumiere electrique (1887); Dunn, " The Photo-retardograph," Journal United States Artillery, 8, p. 29; E. J.

Marey, La Methode graphique (for Deprez accelerographe) ; See also:

Werner See also:Siemens, " Electric Spark Chronograph," Wied. Ann. (1845), 66. (F. J.

End of Article: CHRONOGRAPH

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