[1] See the lists in Driver, _Lit. of Old Test._ pp. 502 sqq.; and the
exhaustive summary by Fr. Brown in Hastings' _Dict. Bible_, i. 289
sqq.
[2] R.V. "commentary," properly, an edifying religious work, a
didactic or homiletic exposition. A distinct tendency to Midrash is
found even here and there in the earlier books.
[3] The problem of the sources is one of considerable intricacy and
cannot be discussed here; the introduction to the commentaries of
Benzinger and Kittel (see _Bibliography_ below) should be consulted.
The questions depend partly upon the view taken of the origin and
structure of the book of Kings (q.v.) and partly upon the results of
historical criticism.
[4] "A careful comparison of Chronicles with Samuel and Kings is a
striking object lesson in ancient historical composition. It is an
almost indispensable introduction to the criticism of the Pentateuch
and the older historical works" (W.H. Bennett, _Chronicles_, p. 20
seq.).
[5] But xxxii. 1-8 may preserve a tradition of the account of the
city's wonderful deliverance mentioned in _Kings_ (see HEZEKIAH), and
the details of the invasion of Judah in the time of Joash differ
essentially from those in the earlier source. Even 2 Chron. viii. 2
cannot be regarded as a _deliberate_ alteration since the writer does
not appear to be quoting from 1 Kings ix. 10 sqq. (the two passages
should be carefully compared), and his view of Solomon's greatness is
already supported by allusions in the earlier but extremely composite
sources in _Kings_ (see SOLOMON).
[6] But that this was not the invention of the chronicler appears
possible from Jer. xxv. 3. Similarly, Hezekiah's reforms are dated in
his first year (2 Chron. xxix. 3), against all probability; see
HEZEKIAH (end).
[7] 2 Chron. xxiii. is an excellent specimen of the redaction to which
older narratives were submitted; cf. also 2 Chron. xxiv. 5 seq. (2
Kings xi. 4 seq.), xxxiv. 9-14 (2 Kings xxii.), xxxv. 1-19 (2 Kings
xxiii. 21-23).
[8] Passages in the books of Samuel and Kings which might appear to
point to the contrary require careful examination; they prove to be
glosses or interpolations, or are relatively late as a whole.
[9] The view that the chronicler _invented_ such narratives is
inconceivable, and in the present stage of historical criticism is
as unsound as an implicit reliance upon those sources in the earlier
books, which in their turn are often long posterior to the events
they record. Although Graf, in a critical and exhaustive study
(_Geschichtlichen Bücher des A.T._, Leipzig, 1866), concluded that
the Chronicles have almost no value as a documentary source of the
ancient history, he subsequently admitted in private correspondence
with Bertheau that this statement was too strong (preface to
Bertheau's _Commentary_, 2nd ed., 1873).
CHRONOGRAPH (from Gr. [Greek: chronos], time, and [Greek: graphein], to
write). 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 WATCH), by means of which the time between events is shown on a
dial, are also called chronographs; they were originally rightly called
chronoscopes ([Greek: skopein], to see).
In the first experiments in ballistics by B. Robins, Count Rumford and
Charles 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
Benjamin Robins, edited by Hutton, 1805, p. 84). It consisted of a
pendulum of considerable weight, which was displaced from its position
of rest by the impact of the 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 form of a long cylinder, weighing about 140 lb,
suspended with its axis horizontal from four wires at each end, all
moving points being provided with knife edges. The true length of
suspension was deduced from observations of the time of a complete small
oscillation. The head of the pendulum was furnished with a wooden block,
which caught the fragments of bullets fired at it, and its displacement
was recorded by a rod moved by the bob (_The Book of the Rifle_, by the
Hon. T.F. Fremantle, p. 336). An improved ballistic pendulum in which
the geometric method of suspension is introduced has been used by A.
Mallock, to determine the resistance of the air to bullets having a
velocity up to 4500 F/S. (_Proc. Roy. Soc._, Nov. 1904). A ballistic
pendulum, carried by a geometric suspension from five points, has also
been employed by C.V. Boys in a research on the elasticity of golf
balls, the displacement of the bob being recorded on a sheet of smoked
glass.[1] For further information on the dynamics of the subject see
_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 period of time is
recorded by means of some kind of electrically controlled mechanism; and
in order that small fractions of a second may be measured, tuning-forks
are employed, giving any convenient number of vibrations per second, a
light style or scribing point, usually of aluminium, being attached to
one of the legs of the tuning-fork. A trace of the vibration is made on
a surface blackened with the deposit from the smoke of a lamp. Glazed
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 movement of the scribing points. If the
surface be cylindrical, thin sheet 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 direct or indirect comparison with the mean solar second,
taken from a standard clock, the rate of which is known from transit
observations ("Recherches sur les vibrations d'un diapason étalon," R.
Koenig, _Wied. Ann._, 1880). 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
interpolation. Regnault (_Mémoires de l'acad. des sciences_, t. xxxvii.)
employed both a standard clock and a tuning-fork in his determination of
the velocity of sound. The effect of temperature on tuning-forks has
been determined by Lord Rayleigh and Professor H. McLeod (_Proc. Roy.
Soc._, 1880, 26, p. 162), who found the coefficient to be 0.00011 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 circuit is broken by a projectile. Another
method is to arrange the terminals of the secondary circuit of an
induction coil, so that when the primary circuit is opened a small spark
punctures or marks a moving surface (Helmholtz, _Phil. Mag._, 1853, p.
6). A photographic plate or film, moving in a dark chamber, is also used
to receive markings produced by a beam of light interrupted by a small
screen attached to an electromagnetic stylus, or by the legs of a
tuning-fork, or by the mercury column of a capillary electrometer. In
certain researches on the explosive wave of gases the light given by the
burning gases made the time trace on a rapidly moving photographic film
(H.B. 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.
Foster, _Text Book of Physiology_, 1879, p. 39).
Grobert and Dabooz.
_Gun Chronographs._--Probably the earliest forms of chronographs, not
based on the ballistic pendulum method, are due to Colonel Grobert,
1804, and Colonel Dabooz, 1818, both officers of the French army. In
the instrument by Grobert two large disks, attached to the same axle
13 ft. apart, were rapidly rotated; the shot pierced each disk, the
angle between two holes giving the time of flight of the ball, when
the angular velocity of the disks was known. In the instrument by
Colonel Dabooz a cord passing over two light pulleys, one 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.
Wheatstone.
In the early form of chronoscope invented by Sir C. Wheatstone in 1840
the period of time was measured by means of a species of clock, driven
by a weight; the dial pointer was started and stopped by the action of
an electromagnet which moved a pawl engaging with a toothed 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 Wheatstone:--"A wooden ring embraced the mouth of
the gun, and a wire connected the opposite sides of the ring. At a
proper distance the target was erected, and so arranged that the least
motion given to it would establish a permanent contact between two
metal points. One of the extremities of the wire of the electromagnet
(before mentioned) was attached to one pole of a small 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."
Henry.
Professor Joseph Henry (_Journal 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 1/1000 second.
The time marks were made by two galvanometer 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 (_Comptes
rendus_, 1845). This chronograph consisted of a cylinder 1 metre in
circumference and 0.36 metre long, driven by clockwork, the rotation
being regulated by a governor provided with wings. A small carriage
geared to the wheelwork traversed its length, carrying electromagnetic
signals. The electric chronograph signal usually consists of a small
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 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 regularity of
rotation of the cylinder, on which each mm. represented 1/1000 second.
Navez.
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 vertical 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 is determined. [Sidenote:
Benton.] 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 ferro-cyanide of 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 traverse of the shot between the screens is
determined.
Bashforth.
In the Bashforth chronograph a platform, arranged to descend slowly
alongside of a vertical rotating cylinder, carries two markers,
controlled by electromagnets, which describe a double 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 series of contact
pieces attached to the screens through which the shot passes in
succession. On the gun range, when the shot reaches the first screen,
it breaks a weighted cotton 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 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.
Noble.
The chronoscope invented by Sir Andrew Noble is so well adapted to the
measurement of very small intervals of time that it is usually
employed to ascertain the velocity acquired by a shot at different
parts of the bore in moving from a 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 loop of wire which forms
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 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-black, and the secondaries of the coils are caused to discharge
against them, so that a 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
vernier, readings are made to thousandths of an inch, and the
peripheral velocity of the disks being 1100 in. a second, the machine
indicates portions of time rather less than one-millionth of a second;
it is, in fact, practically correct to hundred-thousandths of a second
(_Phil. Trans._, 1875, pt. i.).
Le Boulengé.
In the Le Boulengé chronograph ("Chronograph le Boulengé," par M.
Bréger, Commission de Gâvre, Sept. 1880) two screens are used. The
wire of the first forms part of the circuit of an 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 free a spring, and causes a horizontal knife to fly forward and
nick a zinc 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 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 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 recess in
the stand deep enough to receive its full length. The instrument is so
adjusted that the nick thus made is 4.435 in. above the zero point,
corresponding to 0.15 sec. This is the disjunctor reading, and
requires to be frequently corrected during experiments. The instrument
was modified and improved by Colonel H.C. Holden, F.R.S. For further
information respecting formulae relating to it see _Text Book of
Gunnery_ (1857).
Watkin.
The electric chronograph of the late H.S.S. Watkin consists of two
long cylinders rotating on vertical axes, and between them a
cylindrical weight, having a pointed head, is free to fall. 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 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
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 release is such that the falling weight is not subjected, after it
has begun to fall, to a diminishing magnetic field, which would be the
case if it were directly supported by an electromagnet. An 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 mémorial de l'artillerie de la marine_)
devised a chronograph to indicate graphically the motion of recoil of
a cannon when fired. A pillar fixed to the ground at the 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 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 500 complete vibrations per second. A central
line was drawn through the curved path of the tracing point, and every
entire vibration cut the straight line twice, the interval between
each intersection equalling 1/1000 second. The diagram so produced
gave ihe total time of the accelerated motion of recoil of the gun,
the maximum velocity of recoil, and the rate of acceleration of recoil
from the beginning to the end of the motion. By means of an instrument
furnished with a microscope and micrometers, the length and 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 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 constant, v the velocity of the fork at the
midpoint of its path, r the velocity of recoil, [alpha] 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 =
2[pi]a/t; r = v/tan [alpha].
Jervis-Smith.
F. Jervis-Smith's tram chronograph (_Patents_, 1894, 1897, 1903) was
devised for measuring periods of time varying from about one-fourth to
one twenty-thousandth part of a second (_Proc. Roy. Soc._, 1889, 45,
p. 452; _The Tram Chronograph_, by F. Jervis-Smith, 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 vertical
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 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 act. The tram is brought to rest by a gradually
applied brake, consisting of two crossed leather bands stretched by
two springs; a projection from the tram runs between the bands, and
brings it to rest with but little lateral pressure. When, for certain
physiological experiments, a 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 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 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 translation, allow a number of observations to be
made. The traces are counted out on a sloping glass 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 micrometer microscope. When the distance between
the screens is known, and also the time of flight, the midpoint
velocity is found by applying Bashforth's formula. When the velocity
of shot from a shot-gun has to be found, a thin wire stretched across
the muzzle takes the 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 key attached by a cord to the man who loads the
gun and prepares the electric fuse. The firing circuit is closed by
inserting the key in a switch at the rear of the gun, thus preventing
him from getting into the line of fire when the gun is fired by the
chronograph. The tram, when the instrument is adjusted, has a
practically constant velocity of traverse.
Crehore-Squier.
The polarizing photo-chronograph, designed and used by A.C. Crehore
and G.O. Squier at the United States Artillery School (_Trans. Amer.
Inst. Elect. Eng._ vol. 14, and _Journal 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
general arrangement is as follows:--A beam of light from an electric
lamp traverses a lens, then a Nicol 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 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 produce a magnetic field across
the glass cylinder, which is filled with carbon bisulphide, is in
circuit with a dynamo, resistances, and the screens on the gun range.
It is a well-known phenomenon in physics that when, with the
above-mentioned 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 über die Vibration des
Gewehrlaufs_, by C. Cranz and K.R. Koch (Munich, 1899), 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 error
of departure" in ballistics.
Watkin.
In a second chronograph by Watkin ("Chronographs and their Application
to Gun Ballistics," _Proc. Roy. Inst._, 1896), a metal drum, 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 uniform speed.
The points of a row of steel-pointed pins, screwed into a frame of
ebonite, can be brought within 1/200 in. of the surface of the drum.
Each 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 solution of paraffin wax in benzol, which
causes the markings produced by the sparks to be well defined. The
records are read by means of a fine 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.
Deprez.
In the chronograph of Marcel Deprez, a cylinder for receiving records
is driven at a high velocity, 4 to 5 metres per second surface
velocity. The velocity is determined by means of an
electrically-driven tuning-fork, the traces being read by means of a
vernier gauge. A mercury speed indicator of the Ramsbottom type
enables the rotation to be continuously controlled (A. Favarger,
_L'Électricité et ses applications à la chronométrie_).
Dent.
_Astronomical Chronographs._--The astronomical chronograph is an
instrument whereby an observer is enabled to register the time of
transit of a star on a sheet of paper attached to a revolving
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 driving a telescope. By means of a 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 stylographic ink pen. The
point or pen is made to 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 mark. In E.J. Dent's form (_Nature_, 23, p. 59)
continuous observations can be recorded for 6-2/3 hours. The conical
pendulum used to govern the rotation of the cylinder was the invention
of Sir G.B. Airy. The lower end is geared to a metal plate which
sweeps through an annular trough filled with glycerin and water. When
the path of the pendulum exceeds a certain 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 power produces no perceptible difference in the
time. To prevent the injury of the conical pendulum and the wheel work
by any sudden check of the cylinder, a ratch-wheel connexion is placed
between the cylinder and the train of wheel work; this enables the
pendulum to run on until it gradually comes to rest. The pendulum,
which weighs about 18 lb, is compensated, and makes one revolution in
two seconds; it is suspended from a bracket by means of two flexible
steel springs placed at right angles to one another.
The observatory of Washburn, University of Wisconsin, is furnished
with a chronograph of the same type as that of Dent (_Annals Harvard
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 peculiar construction. When the balls fly out beyond a
certain point, one of them engages with a hook attached to a brass
cylinder which embraces the vertical axle loosely. When this mass is
pulled aside the work done on it diminishes the speed of the governor.
The pendulum ball usually strikes the hook from 60 to 70 times per
minute. Governors on this principle were adopted by Alvan Clark for
driving heliostats in the United States Transit of Venus Expedition,
1874.
Grubb.
In the astronomical chronograph designed by Sir Howard Grubb (_Proc.
Inst. Mech. Eng._, July 1888), the recording cylinders--two in
number--are driven by a weight acting on a train of wheel work
controlled by an astronomical telescope governor. The peculiar feature
of this instrument is that the axle is geared to a 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 hour and minute, and, by pressing
a contact key attached to a flexible cord at the transit instrument,
marks the paper with a letter in Morse telegraph characters,
indicating the hour and minute; he then 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 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 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.
Hipp.
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, controlled by a
vibrating metal tongue; this important feature is described in detail
in Favarger's work cited above.
Regnault.
_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 pipe, a band of paper 27 mm. wide was
continuously unrolled from a bobbin by means of an electromagnetic
engine. In its passage over a pulley it passed over a smoky lamp
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 band, 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 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
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 pistol into the pipe
furnished with diaphragms and contact pieces.
Ayrton and Perry.
In the chronographic use of the Morse telegraph instrument (Stewart
and Gee, _Elementary Practical Phys._ p. 234) a circuit is arranged
which includes a seconds' pendulum furnished with a fine 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-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
otherwise 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 (_Proc. Phys. Soc. Lond._ 3, p. 268).
Hipp.
Mayer.
In the tuning-fork electro-chronograph attributed to Hipp a metal
cylinder covered with smoked glazed paper is rotated uniformly 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 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 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 lead plates in dilute
sulphuric acid as a shunt across the battery circuit.
Fick.
_For Physiological Purposes._--A. Fick's pendulum myograph or
muscle-trace recorder is described in _Vierteljahrsschr. der
naturforsch. Ges. in Zürich_, 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 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 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.
Du Bois Reymond.
In the spring myograph of E. Du Bois Reymond (Munk's _Physiologie des
Menschen_, p. 398) a smoked glass plate attached to a metal rod is
shot by a spiral spring along two guides with a 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.
Burch.
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
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 this
instrument.
Marey.
An important development of a branch of chronography is due to E.J.
Marey (_Comptes rendus_, 7. août 1882, and _Le Mouvement_, par E.J.
Marey, Paris, 1894), who employed a photographic plate for receiving
successive pictures of moving objects, at definite times, when
investigating the movements of animals, birds, fishes, insects, and
also microscopic objects such as vorticellae. The instrument in one of
its forms consisted of a 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 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 Méthode 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 fan governor, and
pneumatic signal, constructed thus. One end of a closed shallow
cylinder, about 4 cm. dia., is furnished with a stretched 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 body of the
animal the movement of which is under investigation. The 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 "tambour à 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
physikalisch-medicinischen Gesellschaft in Würzburg_ (1872); Harless,
"Das Attwood'sche Myographion," _Abhandlungen der k. bayerischen
Akademie der Wissenschaften_ (1862); Id., _Fall-Myographion
aufgestellt in der Wiener Weltausstellung in der Abteilung für das
Unterrichtswesen von Ungarn_ (Budapest, 1873); Hensen, "Myographion
mit vibratorischer Bewegung," _Arbeiten aus dem Kieler physiol.
Instit._ (1868); Brücke, _Sitzungsber. d Wien. Acad._ (1877); Pflüger,
"Myographion ohne Bewegung," _Untersuchungen über die Physiologie des
Electrotonus_ (1859); Pouillet, _Compt. rend._ (1844); I. Munk,
_Physiologie des Menschen_ (for Pflüger's cylinder governed by conical
pendulum); J.G. M'Kendrick, _Life in Motion_ (1892) (for early form of
cylinder chronograph by Thomas Young); Stirling, _Outlines of
Practical Physiology_ (for reaction-time chronographs of F. Galton and
Exner). (2) Chronographs used in gun work and for other purposes:
Sabine, _Phil. Mag._ (1876); Moisson, _Notice sur la chronographie
système Schultz_ (Paris, 1875); Paul la Cour, _La Roue phonique_
(Copenhagen, 1878); 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'Arsonval, _La Lumière électrique_ (1887); Dunn, "The
Photo-retardograph," _Journal United States Artillery_, 8, p. 29; E.J.
Marey, _La Méthode graphique_ (for Deprez accélérographe); Werner
Siemens, "Electric Spark Chronograph," _Wied. Ann._ (1845), 66.
(F. J. J. -S.)