improvement being the addition of a fly vane, which, however, had
previously been used for remontoires to steady the motion. He tried
various modifications of construction, but finally adopted the
"four-legged" and "double-three-legged" forms as being the most
satisfactory, the former for regulators and the latter for large
clocks. Fig. 19 is a back view of the escapement part of an
astronomical clock with the four-legged wheel; seen from the front the
wheel would turn the other way. The long locking teeth are made about
2 in. long from the centre, and the lifting pins, of which four point
forwards while four other intermediate ones point backwards, are at
not more than 1/30 of the distance between the centres EC, of the
scape-wheel and pallets; or rather C is the top of the pendulum spring
to which the pallets Cs, Cs' converge, though the resultant of their
action is a little below C. It is not worth while to crank them as
Bloxam did, in order to make them coincide exactly with the top of the
pendulum, as the friction of the beat pins on the pendulum is
insignificant, and even then would not be quite destroyed. The pallets
are not in the same plane, but one is behind and the other in front of
the wheel, with one stop pointing backwards and the other forwards to
receive the teeth alternately--it does not matter which; in this
figure the stop s is behind and the stop s' forward. The pendulum is
now going to the right, and just beginning to lift the right pallet
and free the stop s'; then the wheel will begin to turn and lift the
other pallet by one of the pins which is now lowest, and which moves
through 45 deg. across the line of centres, and therefore lifts with
very little friction. It goes on till the tooth now below s reaches s
and is stopped there. Meanwhile the pallet Cs' goes on with the
pendulum as far as it may go, to the end of the arc which we have
called [alpha], starting from [gamma]; but it falls with the pendulum
again, not only to [gamma] but to -[gamma] on the other side of 0, so
that the impulse is due to the weight of each pallet alternately
falling through 2[gamma]; and the magnitude of the impulse also
depends on the obliqueness of the pallet on the whole, i.e. on the
distance of its centre of gravity from the vertical through C. The fly
KK' is set on with a friction spring like the common striking-part
fly, and should be as long as there is room for, length being much
more effective than width.
The double three-legged gravity escapement, which was first used in
the Westminster clock, is shown in fig. 20. The principle of it is the
same as of the four-legs; but instead of the pallets being one behind
and the other in front of the wheel, with two sets of lifting pins,
there are two wheels ABC, abc, with the three lifting pins and the two
pallets between them like a lantern pinion. One stop B points forward
and the other A backward. The two wheels have their teeth set
intermediately or 60 deg. apart, though that is not essential, and the
angle of 120 deg. may be divided between them in any other
proportions, as 70 deg. and 50 deg., and in that way the pallets may
be still more oblique than 30 deg. from the vertical, which, however,
is found enough to prevent tripping even if the fly gets loose, which
is more likely to happen from carelessness in large clocks than in
astronomical ones.
Of course the fly for those escapements in large clocks, with weights
heavy enough to drive the hands in all weather, must be much larger
than in small ones. For average church clocks with 1-1/4 sec. pendulum
the legs of the scape-wheels are generally made 4 in. long and the fly
from 6 to 7 in. long in each vane by 1-1/4 or 1-1/2 wide. For 1-1/2 sec.
pendulums the scape-wheels are generally made 4-1/2 radius. At
Westminster they are 6 in.
Lord Grimthorpe considered that these escapements act better,
especially in regulators, if the pallets do not fall quite on the
lifting pins, but on a banking, or stop at any convenient place, so as
to leave the wheel free at the moment of starting; just as the
striking of a common house clock will sometimes fail to start unless
the wheel with the pins has a little run before a pin begins to lift
the hammer. The best way to manage the banking is to make the
beat-pins long enough to reach a little way behind the pendulum, and
let the banking be a thin plate of any metal screwed adjustably to the
back of the case. This plate cannot well be shown in the drawings
together with the pendulum, which, it may be added, should take up one
pallet just when it leaves the other.
[Illustration: FIG. 21.--Chronometer Spring Remontoire.]
Chronometer spring remontoire.
In chronometer spring remontoires the pendulum, as it goes by, flips a
delicate spring and releases a small weight or spring which has been
wound up in readiness by the action of the scape-wheel and which by
leaping on to the pendulum gives it a push. One on this principle made
about the middle of the 19th century by Robert Houdin is to be seen at
the Conservatoire des Arts et Metiers. It is very complicated. The
following is more simple. In fig. 21 a scape-wheel AB has 30 pins and
360 teeth. It is engaged with a fly vane EP mounted on a pinion of 12
teeth. Each pin as it passes raises an impulse arm CD which is hooked
upon a detent K. A pall NM then engages the fly vane and prevents the
scape-wheel from moving farther. The impulse arm being now set, as the
plate F attached to the lower end of the pendulum flies past from left
to right a pall G knocks aside the detent K, and allows a pin O
projecting from the end of the impulse arm to fall upon an inclined
pallet h, which is thus urged forward. As soon as the pallet has left
the pin, the impulse arm in its further fall strikes N, which
disengages the pall at P and allows the scape-wheel to move on and
again wind up the impulse arm CD, which is then again locked by the
detent K. On the return journey of the pendulum the light pall G,
which acts the part of a chronometer spring, flips over the detent.
The pallet is double sided, h and h', so that if by chance the clock
runs down while the pendulum swings from left to right the impulse arm
will be simply raised and not smashed. It has a flat apex, on which
the pin falls before descending. The impulse given depends on the
weight of the impulse arm and may be varied at pleasure. The work done
in unlocking the detent is invariable, as it depends on the pressure
of the fly vane at P and is independent of the clock-train. The
duration of the impulse is very short--only about 1/10 of the arc of
swing. It is given exactly at the centre of the swing, and when not
under impulse the pendulum is detached.
_Clock Wheels._--Since, as we have seen, any increase in the arc of a
pendulum is accompanied by a change in its going rate, it is very
desirable to keep the force which acts on the pendulum uniform. This in
fact is the great object of the best escapements. Inasmuch as the
impulse on the pendulum, derived from the work done by a falling weight
or an unwinding spring, is transmitted through a train of wheels, it is
desirable that that transmission should be as free from friction and as
regular as possible. This involves care in the shaping of the teeth. The
object to be aimed at is that as the wheel turns round the ratio of the
power of the driver to that of the driven wheel ("runner" or "follower")
should never vary. That is to say, whether the back part of the tooth of
the driver is acting on the tip of the tooth of the follower, or the tip
of the driver is acting on the back part of the tooth of the follower,
the leverage ratio shall always be uniform. For simplicity of
manufacture the pinion wheels are always constructed with radial leaves,
so that the surface of each tooth is a plane passing through the axis of
the wheel. The semicircular rounding of the end of the tooth is merely
ornamental. The question therefore is, suppose that it is desired by
means of a tooth on a wheel to push a plane round an axis, what is the
shape that must be given to that tooth in order that the leverage ratio
may remain unaltered?
Epicycloidal teeth.
If a curved surface, known as a "cam," press upon a plane one, both
being hinged or centred upon pivots A and B respectively (fig. 22), then
the line of action and reaction at D, the point where they touch, will
be perpendicular to their surfaces at the point of contact--that is
perpendicular to BD, and the ratio of leverage will obviously be AE:BD,
or AC:CB. Hence to cause the leverage ratio of the cam to the plane
always to remain unaltered, the cam must be so shaped that in any
position the ratio AC:CB will remain unchanged. In other words the shape
of the cam must be such that, as it moves and pushes BD before it, the
normal at the point of contact must always pass through the fixed point
C.
[Illustration: FIG. 22.--Cam and Plane.]
[Illustration: FIG. 23.]
[Illustration: FIG. 24.]
If a circle PMB roll upon another circle SPT (fig. 23) any point M on it
will generate an epicycloid MN. The radius of curvature of the curve at
M will always be MP, for the part at M is being produced by rotation
round the point P. It follows that a line from B to M will always be
tangential to the epicycloid. If the epicycloid be a cam moving as a
centre round the centre R (not shown in the figure) of the circle SPT,
the leverage it will exert upon a plane surface BM moving round a
parallel axis at B, will always be as BP to PR, that is, a constant;
whence MN is the proper shape of a tooth to act on a pinion with radial
arms and centred at B. In designing a pair of wheels to transmit motion,
which is to be multiplied say 6 times in the transmission (about the
usual ratio for clock wheels), if we take two circles (called the "pitch
circles") touching one another with radii as 1:6, then the circumference
of the smaller will roll 6 times round that of the larger. The smaller
wheel will have a number of teeth, say 8 to 16, each of them being
sectors of the circle (fig. 24). If there are 16 teeth, then on the
surface of the driving wheel there will be 96 teeth. Each of these teeth
will be shaped as the curve of an epicycloid formed by the rolling on
the big circle of a circle whose diameter is the radius of the pitch
circle of the pinion. Points of the teeth so formed are cut off, so as
to allow of the pinion having a solid core to support it, and gaps are
made into the pitch circle to admit the rounded ends of the leaves of
the pinon wheel. Thus a cog-wheel is shaped out.
Clock wheels are made of hard hammered brass cut out by a wheel cutting
machine. This machine consists of a vertical spindle on the top of which
the wheel to be cut is fixed on a firmly resisting plate of metal of
slightly smaller diameter, so as to allow the wheel to overlap. A cutter
with the edges most delicately ground to the exact shape of the gap
between two teeth is caused to rotate 3000 - 4000 times a minute, and
brought down upon the edge of the wheel. The shavings that come off are
like fine dust, but the cutter is pushed on so as to plunge right
through the rim of the wheel in a direction parallel to the axis. In
this way one gap is cut. The vertical spindle is now rotated one
division, by means of a dividing plate, and another tooth is cut, and so
the operation goes on round the wheel.
It is not desirable in clocks that the pinion wheels which are driven
should have too few teeth, for this throws all the work on a pair of
surfaces before the centres and is apt to produce a grinding motion.
Theoretically the more leaves a pinion has the better. Pinions can be
made with leaves of thin steel watch-spring. In this case quite small
pinions can have 20 leaves or more. The teeth in the driving wheels then
become mere notches for which great accuracy of shape is not necessary.
Such wheels are easy to make and run well. Lantern pinions are also
excellent and are much used in American clocks. They are easy to make in
an ordinary lathe. The cog-wheels must, however, be specially shaped to
fit them. They consist of a number of round pins arranged in a circle
round the axis of the wheel and parallel to it. The ends are secured in
flanges like the wires of a squirrel cage. The teeth of cog-wheels
engage them and thus drive the wheel round. They were much used at one
time but are now falling out of favour again.
Involute teeth.
It is possible to make toothed wheels that drive with perfect uniformity
by using for the curve of the teeth involutes of circles. These
involutes are traced out by a point on a string that is gradually
unwound from a circle. They are in fact epicycloids traced by a rolling
circle of infinite radius, i.e. a straight line. Involute teeth have the
advantage that they roll on one another instead of sliding. When badly
made they put considerable strain on the axes or shafts that carry them.
Hence they have not been regarded with great favour by clockmakers.
Pitch.
By the pitch of a wheel is meant the number of teeth to the inch of
circumference or diameter of the wheel; the former is called the
circumferential pitch, the latter the diametral pitch. Thus if we say
that a wheel has 40 diametral pitch we mean that it has 40 teeth to each
inch of diameter. The circumferential pitch is of course got by dividing
the diametral pitch by [pi]. Wheel-cutters are made for all sizes of
pitches. If it were needed to make a pair of wheels the ratio of whose
motion was say 6:1 and we determined to use a diametral pitch of 30 to
the inch, that is teeth about 1/10 in. wide at the base, and if the
smaller circle were to have 20 teeth, we should need a blank of a
diameter of 20/30 + 2/30 = 22/30 in. for the smaller wheel, and one of
120/30 + 2/30 = 122/30 in. for the larger wheel which would have 120
teeth to the inch and be 4.06 in diameter to the tips of the teeth. The
smaller toothed wheel would be .73 of an inch in diameter over all. The
pitch circles of the wheels would be 2/3 and 4 in. respectively. For
fine wheel work, where the driver is always much larger than the driven
wheel, the epicycloidal tooth appears preferable, as it is generally
considered to put less side strain on the pinion wheel. But the relative
merits of the two systems have never been properly tested for clock
work.
_Going Barrels._--A clock which is capable of going accurately must have
some contrivance to keep it going while it is being wound up. In the
old-fashioned house clocks, which were wound up by merely pulling one of
the strings, and in which one such winding served for both the going and
striking parts, this was done by what is called the endless chain of
Huygens, which consists of a string or chain with the ends joined
together, and passing over two pulleys on the arbors of the great
wheels, with deep grooves and spikes in them, to prevent the chain from
slipping. In one of the two loops or festoons which hang from the upper
pulleys is a loose pulley without spikes, carrying the clock-weight, and
in the other a small weight only heavy enough to keep the chain close to
the upper pulleys. Now, suppose one of those pulleys to be on the arbor
of the great wheel of the striking part, with a ratchet and click, and
the other pulley fixed to the arbor of the great wheel of the going
part; then (whenever the clock is not striking) the weight may be pulled
up by pulling down that part of the string which hangs from the other
side of the striking part; and yet the weight will be acting on the
going part all the time. It would be just the same if the striking part
and its pulley were wound up with a key, instead of the string being
pulled, and also the same, if there were no striking part at all, but
the second pulley were put on a blank arbor, except that in that case
the weight would take twice as long to run down, supposing that the
striking part generally requires the same weight x fall as the going
part.
[Illustration: FIG. 25.--Harrison's Going-Ratchet.]
This kind of going barrel, however, is evidently not suited to the
delicacy of an astronomical clock; and Harrison's going ratchet is now
universally adopted in such clocks, and also in chronometers and watches
for keeping the action of the train on the escapement during the
winding. Fig. 25 (in which the same letters are used as in the
corresponding parts of fig. 3) shows its construction. The click of the
barrel-ratchet R is set upon another larger ratchet-wheel with its teeth
pointing the opposite way, and its click rT is set in the clock frame.
That ratchet is connected with the great wheel by a spring ss' pressing
against the two pins s in the ratchet and s' in the wheel. When the
weight is wound up (which is equivalent to taking it off), the click Tr
prevents that ratchet from turning back or to the right; and as the
spring ss' is kept by the weight in a state of tension equivalent to the
weight itself it will drive the wheel to the left for a short distance,
when its end s is held fast, with the same force as if that end was
pulled forward by the weight; and as the great wheel has to move very
little during the short time the clock is winding, the spring will keep
the clock going long enough.
In the commoner kind of turret clocks a more simple apparatus is used,
which goes by the name of the _bolt and shutter_, because it consists of
a weighted lever with a broad end, which shuts up the winding-hole. When
it is lifted a spring-bolt attached to the lever, or its arbor, runs
into the teeth of one of the wheels, and the weight of the lever keeps
the train going until the bolt has run itself out of gear. Clocks are
not always driven by weights. When accuracy is not necessary, but
portability is desirable, springs are used. The old form of spring
became weaker as it was unwound and necessitated the use of a device
called a fusee or spiral drum. This apparatus will be found described in
the article WATCH.
_Striking Mechanism._--There are two kinds of striking work used in
clocks. The older of them, the _locking-plate_ system, which is still
used in most foreign clocks, and in turret clocks in England also, will
not allow the striking of any hour to be either omitted or repeated,
without making the next hour strike wrong; whereas in the _rack_ system,
which is used in all English house clocks, the number of blows to be
struck depends merely on the position of a wheel attached to the going
part, and therefore the striking of any hour may be omitted or repeated
without deranging the following ones. We shall only describe the second
of these, which is the more usual in modern timepieces.
Fig. 26 is a front view of a common English house clock with the face
taken off, showing the repeating or rack striking movement. Here, as in
fig. 3, M is the hour-wheel, on the pipe of which the minute-hand is
set, N the reversed hour-wheel, and n its pinion, driving the 12-hour
wheel H, on whose socket is fixed what is called the snail Y, which
belongs to the striking work exclusively. The hammer is raised by the
eight pins in the rim of the second wheel in the striking train, in the
manner which is obvious.
[Illustration: FIG. 26.--Front view of common English House Clock.]
The hammer does not quite touch the bell, as it would jar in striking if
it did, and prevent the full sound. The form of the hammer-shank at the
arbor where the spring S acts upon it is such that the spring both
drives the hammer against the bell when the tail T is raised, and also
checks it just before it reaches the bell, the blow on the bell thus
being given by the hammer having acquired momentum enough to go a little
farther than its place of rest. Sometimes two springs are used, one for
impelling the hammer, and the other for checking it. But nothing will
check the chattering of a heavy hammer, except making it lean forward so
as to act, partially at least, by its weight. The pinion of the
striking-wheel generally has eight leaves, the same number as the pins;
and as a clock strikes 78 blows in 12 hours, the great wheel will turn
in that time if it has 78 teeth instead of 96, which the great wheel of
the going part has for a centre pinion of eight. The striking-wheel
drives the wheel above it once round for each blow, and that wheel
drives a fourth (in which there is a single pin P), six, or any other
integral number of turns, for one turn of its own, and that drives a
fan-fly to moderate the velocity of the train by the resistance of the
air, an expedient at least as old as De Vick's clock in 1379.
The wheel N is so adjusted that, within a few minutes of the hour, the
pin in it raises the _lifting-piece_ LONF so far that that piece lifts
the click C out of the teeth of the _rack_ BKRV, which immediately falls
back (helped by a spring near the bottom) as far as its tail V can go by
reason of the snail Y, against which it falls; and it is so arranged
that the number of teeth which pass the click is proportionate to the
depth of the snail; and as there is one step in the snail for each hour,
and it goes round with the hour-hand, the rack always drops just as many
teeth as the number of the hour to be struck. This drop makes the noise
of "giving warning." But the clock is not yet ready to strike till the
lifting piece has fallen again; for, as soon as the rack was let off,
the tail of the _gathering pallet_ G, on the prolonged arbor of the
third wheel, was enabled to pass the pin K of the rack on which it was
pressing before, and the striking train began to move; but before the
fourth wheel had got half round, its pin P was caught by the end of the
lifting-piece, which is bent back and goes through a hole in the plate,
and when raised stands in the way of the pin P, so that the train cannot
go on till the lifting-piece drops, which it does exactly at the hour,
by the pin N then slipping past it. Then the train is free; the striking
wheel begins to lift the hammer, and the gathering pallet gathers up the
rack, a tooth for each blow, until it has returned to the place at which
the pallet is stopped by the pin K coming under it. In this figure the
lifting-piece is prolonged to F, where there is a string hung to it, as
this is the proper place for such a string when it is wanted for the
purpose of learning the hour in the dark, and not (as it is generally
put) on the click C; for if it is put there and the string is held a
little too long, the clock will strike too many; and if the string
accidentally sticks in the case, it will go on striking till it is run
down--neither of which things can happen when the string is put on the
lifting-piece.
The snail is sometimes set on a separate stud with the apparatus called
a _star-wheel_ and _jumper_. On the left side of the frame we have
placed a lever x, with the letters st below it, and si above. If it is
pushed up to si, the other end will come against a pin in the rack, and
prevent it from falling, and will thus make the clock silent; and this
is much more simple than the old-fashioned "strike and silent"
apparatus, which we shall therefore not describe, especially as it is
seldom used now.
If the clock is required to strike quarters, a third "part" or train of
wheels is added on the right hand of the going part; and its general
construction is the same as the hour-striking part; only there are two
more bells, and two hammers so placed that one is raised a little after
the other. If there are more quarter-bells than two, the hammers are
generally raised by a chime-barrel, which is merely a cylinder set on
the arbor of the striking-wheel (in that case generally the third in the
train), with short pins stuck into it in the proper places to raise the
hammers in the order required for the tune of the chimes. The quarters
are usually made to let off the hour, and this connexion may be made in
two ways. If the chimes are different in tune for each quarter, and not
merely the same tune repeated two, three and four times, the repetition
movement must not be used for them, as it would throw the tunes into
confusion, but the old locking-plate movement, as in turret clocks; and
therefore, if we conceive the hour lifting-piece connected with the
quarter locking-plate, as it is with the wheel N, in fig. 26, it is
evident that the pin will discharge the hour striking part as the fourth
quarter finishes.
But where the repetition movement is required for the quarters, the
matter is not quite so simple. The principle of it may shortly be
described thus. The quarters themselves have a rack and snail, &c., just
like the hours, except that the snail is fixed on one of the hour-wheels
M or N, instead of on the twelve-hour wheel, and has only four steps in
it. Now suppose the quarter-rack to be so placed that when it falls for
the fourth quarter (its greatest drop), it falls against the hour
lifting-piece somewhere between O and N, so as to raise it and the click
C. Then the pin Q will be caught by the click Qq, and so the
lifting-piece will remain up until all the teeth of the quarter-rack are
gathered up; and as that is done, it may be made to disengage the click
Qq, and so complete the letting off the hour striking part. This click
Qq has no existence except where there are quarters.
The method in which an alarum is struck may be understood by reference
to either of the recoil escapements (figs. 1 and 7). If a short hammer
instead of a long pendulum be attached to the axis of the pallets, and
the wheel be driven with sufficient force, it will evidently swing the
hammer rapidly backwards and forwards; and the position and length of
the hammer-head may be so adjusted as to strike a bell inside, first on
one side and then on the other. As to the mode of letting off the alarum
at the time required: if it was always to be let off at the same time
all that would be necessary would be to set a pin in the twelve-hour
wheel at the proper place to raise the lifting-piece which lets off the
alarum at that time. But as the time must be capable of alteration, this
discharging pin must be set in another wheel (without teeth), which
rides with a friction-spring on the socket of the twelve-hour wheel,
with a small movable dial attached to it, having figures so arranged
with reference to the pin that whatever figure is made to come to a
small pointer set as a tail to the hour hand, the alarum shall be let
off at that hour.
The _watchman's_ or _tell-tale_ clock, used when it is desired to make
sure of a watchman being on the spot and awake all the night, is a clock
with a set of spikes, generally 48 or 96, sticking out all round the
dial, and a handle somewhere in the case, by pulling which one of the
spikes which is opposite to it, or to some lever connected with it is
pressed in. This wheel of spikes is carried round with the hour-hand,
which in these clocks is generally a twenty-four hour one. It is evident
that every spike which is seen still sticking out in the morning
indicates that at the particular time to which that spike belongs the
watchman was not there to push it in--or at any rate, that he did not.
At some other part of their circuit, the inner ends of the pins are
carried over a roller or an inclined plane which pushes them out again
ready for business the next night. The time at which workmen arrive at
their work may be recorded by providing each of them with a numbered key
with which he stamps his number on a moving tape, on which also the time
is marked by a clock.
_Church and Turret Clocks._--Seeing that a clock--at least the going
part of it--is a machine in which the only work to be done is the
overcoming of its own friction and the resistance of the air, it is
evident that when the friction and resistance are much increased it may
become necessary to resort to expedients for neutralizing their effects,
which are not required in a smaller machine with less friction. In a
turret clock the friction is enormously increased by the great weight of
all the parts; and the resistance of the wind, and sometimes snow, to
the motion of the hands, further aggravates the difficulty of
maintaining a constant force on the pendulum; and besides that, there is
the exposure of the clock to the dirt and dust which are always found in
towers, and of the oil to a temperature which nearly or quite freezes it
all through the usual cold of winter. This last circumstance alone will
generally make the arc of the pendulum at least half a degree more in
summer than in winter; and inasmuch as the time is materially affected
by the force which arrives at the pendulum, as well as the friction on
the pallets when it does arrive there, it is evidently impossible for
any turret clock of the ordinary construction, especially with large
dials, to keep any constant rate through the various changes of
temperature, weather and dirt to which it is exposed. Hence special
precautions, such as the use of remontoires and gravity escapements,
have to be observed in the design of large clocks that have any
pretensions to accuracy, in order to ensure that the arc of the pendulum
is not affected by external circumstances, such as wind-pressure on the
hands or dirt in the wheel-train. But such have been the improvements
effected in electric clocks, that rather than go to the trouble and
expense required by such precautions, it appears far preferable to keep
an accurate time-piece in some sheltered position and use it with a
source of electricity to drive the hands of the large dial.
_Electrical Clocks._--One of the first attempts to apply electricity to
clocks was made by Alexander Bain in 1840-1850. About the same time Sir
C. Wheatstone, R. L. Jones, C. Shepherd, Paul Garnier and Louis Breguet
invented various forms of electrical time-keepers. It is not proposed
here to go into the history of these abortive attempts. Those who desire
to follow them may consult Bain, _An Account of Some Applications of the
Electric Fluid to the Useful Arts_ (1843) and _Short History of Electric
Clocks_ (1852); Sir Charles Wheatstone, _Trade Circular of the British
Telegraph Manufactory_; C. Shepherd, _On the Application of
Electro-magnetism as a Motor for Clocks_ (1851), and a list of
references in the Appendix to Tobler's _Die electrischen Uhren_
(Leipzig, 1883), and a list of books given by F. Hope Jones, _Proc.
Inst. Elec. Eng._, 1900, vol. 29. The history of electrical clocks is a
long and complicated matter, for there are some 600 or 700 patents for
these clocks in Europe and America, some containing the germs of
valuable ideas but most pure rubbish. All that can be done is to select
one or two prominent types of each class and give a brief description of
their general construction.
[Illustration: FIG. 27.--Turret Clock for Hidalgo, Mexico, driving four
8 ft. dials.]
It is in the apparently simple matter of making and keeping the
electrical contact that most of the systems of electrical time-keeping
have failed, for want of attention to the essential conditions of the
problem. In practice every metal is covered with a thin film of
non-conducting oxide over which is another film of moisture, oil, dirt
or air. Hence what is wanted is a good vigorous push of a blunted point
or edge preferably obliquely upon a more or less yielding surface so as
to get a rubbing action. Thus if the stiff spring a b (fig. 28) were
stabbed down on the oblique surface C D a good contact would invariably
result, provided that the metals employed were gold, platinum or some
not easily oxidizable metal. Or again, if a mercury surface be simply
touched with a pin, the slight sparking that is produced on making the
current will soon form a little pile of dirty oxide at the point of
entry, and the contact will frequently fail. If it be necessary to have
a mercury contact, the pin must be well driven in below the surface of
the mercury or else swept through it as an oar is swept through the
water. Another form of electrical contact that acts well is a knife edge
brought into contact with a series of fine elastic strips of metal laid
parallel to one another like the fingers of a hand. The best metal for
contacts, if they are to bear hard usage, is either silver or gold or a
mixture of 40% iridium with 60% of platinum. A pressure of some 15
grammes, at least, is needful to secure a good contact.
[FIG. 28.]
As to the source of current for driving electrical clocks, if Leclanche
cells be used they should preferably be kept in the open air under cover
so as not to dry up. If direct electric current is available from
electric light mains or the accumulators used for lighting a private
house, so much the better. Of course the pressure of 50 or 100 volts
used for lighting would be far too great for clock-driving, where only
the pressure of a few volts is required. But it is easy by the insertion
of suitable resistances, as for instance one or more incandescent lamps,
to weaken down the pressure of the lighting system and make it available
for electric clocks, bells or other similar purposes.
Electricity is applied to clocks in three main ways:--(1) in actuating
timepieces which measure their own time and must therefore be provided
with pendulums or balance wheels; (2) in reproducing on one or more
dials the movements of the hands of a master clock, by the aid of
electric impulses sent at regular intervals, say of a minute or a
half-minute; and (3) in synchronizing ordinary clocks by occasional
impulses sent from some accurate regulator at a distance.
Electrically driven timepieces may be divided under two heads:--(a)
those in which the electric current drives either the pendulum or some
lever which operates upon it, which lever or pendulum in turn drives the
clock hands; and (b) those timepieces which are driven by a weight or
spring which is periodically wound up by electricity--in fact electrical
remontoires.
[Illustration: FIG. 29.--Electrical Clock (faulty design).]
The simplest clock of the first character that could be imagined would
be constructed by fastening an electromagnet with a soft iron core to
the bottom of a pendulum, and causing it to be attracted as the pendulum
swings by another electromagnet fixed vertically under it (fig. 29). As
the pendulum approached the vertical and was say half an inch from its
lowest point, the current would be switched on, and switched off as soon
as the pendulum got to its lowest point. A very small attraction with
this arrangement, probably about a grain weight, acting through the 1/2
in. would drive a heavy pendulum. A switch would have to be worked in
connexion with the pendulum. A strip of ebonite with a small face of
metal on the end of one side, such as a b (fig. 29) might be pivoted at
one end on the pendulum with a weak spring to keep it where free along
the rod. As the pendulum swung by this would be swept on its journey
from left to right against a fixed pin P. This would complete the
electric circuit down through the pendulum rod, round the coil on the
bottom of the pendulum, through the switch into the pin P, thence
through the fixed electromagnet, and so back to the battery. On the
return journey no contact would be made because only the ebonite face of
the switch would touch P. The pendulum would thus receive an impulse
every other vibration. We have described this switch, not to advocate
it, but to warn against its use. For the contact would be quite
insufficient. In order that the switch might not unduly retard the
pendulum it must be light, but this would make the pressure on P too
light to be trustworthy. Moreover, the strength of the impulse would
vary with the strength of the battery, and hence the arc would be
repeatedly uneven.
In contrast with this, let us consider a clock that is now giving
excellent results at the Observatory of Neuchatel in Switzerland on
Hipp's system (_La Pendule electrique de precision_, Neuchatel, 1884 and
1891). The pendulum (fig. 30) consists of two rods of steel joined by
four bridges, one just below the suspension spring, the next about 12
in. lower, the next about half way down, and the last supporting a glass
vessel of mercury which forms the bob. On the third of them is placed an
iron armature, which works between the poles of an electromagnet fixed
to the case, and by which the pendulum is actuated. The circuit is
closed and broken by a flipper, which is swayed to and fro by a block
fixed to the pendulum at the second bridge. As long as the flipper is
merely swayed, no contact takes place, but when the arc of vibration of
the pendulum is diminished the flipper does not clear the block but is
caught by a nick in it, and forced downwards. In this way the circuit is
closed. Fig. 31 is a diagram of the apparatus. When the block g attached
to the pendulum catches and presses down the flipper s, the lever l l is
rocked over, so that a contact is made at k, and the current which
enters the lever l through the knife edge m, runs through the second
lever n n, down through the knife edge o, to the battery, and through
the electromagnet b which causes the armature a to be attracted. As the
block g goes on and releases s, the lever l again falls upon the rest p,
the lever n follows it a part of the way till it is stopped by the
contact q; this shortcircuits the electromagnet and prevents to a large
extent the formation of an induced current. It is claimed that sparking
is by this method almost entirely avoided. It is only when s is caught
in the notch of the block g that s is pressed down, so that the electric
attraction only takes place every few vibrations. This ingenious
arrangement makes the working of the clock nearly independent of the
strength of the battery, for if the battery is strong the impulses are
fewer and the _average arc_ remains the same. The clock is enclosed in
an airtight glass case so as to avoid barometric error. It was tested in
1905 at the Neuchatel observatory. In winter in a room of a mean
temperature of 35 deg. F. it was 1/4 sec. too slow, in summer when the
temperature was 70 deg., it was 1/2 sec. too fast. In the succeeding
winter it became .53 sec. too slow again, thus gaining a little in
summer and losing in winter. Its average variation from its daily rate
was, however, only .033 sec.
[Illustration: FIG. 30.--Hipp Electrical Clock (Peyer, Favarger et
Cie.).]
[Illustration: FIG. 31.--Contact Arrangement of Hipp Clock.]
In another system originated by G. Froment, a small weight is raised by
electricity and allowed to fall upon an arm sticking out at right angles
to the pendulum in the plane of its motion, so as to urge it onwards.
The weight is only allowed to rest on the arm during the downward swing
of the pendulum. The method is not theoretically good, as the impulse is
given at the end of the vibration of the pendulum instead of at its
middle position.
In the clock invented by C. Fery (chef des travaux pratiques at the
Ecole de Physique et Chimie, Paris), an electric impulse is given at
every vibration, not by a battery but by means of the uniform movement
of an armature which is alternately pulled away from and pushed towards
a permanent horseshoe magnet. Currents are thus induced in a bobbin of
fine wire placed between the poles of the horseshoe magnet. The
movements of the armature are produced by another horseshoe magnet
actuated by the primary current from a battery which is turned on and
off by the swinging of the pendulum. The energy of the induced current
that drives the clock depends solely on the total movement of the
armature, and is independent of whether that movement be executed slowly
or rapidly, and therefore of the strength of the battery.
[Illustration: FIG. 32.--Hope Jones Electrical Remontoire.]
_Electrical remontoires_ possess great advantages if they can be made to
operate with certainty. For they can be made to wind up a scape-wheel
just as is done in the case of the arrangement shown in fig. 16 so as to
constitute a spring remontoire, or better still they can be made to
raise a weight as in the case of the gravity train remontoire (fig. 15)
but without the complications of wheel-work shown in that contrivance.
Of this type one of the best known is that of H. Chesters Pond. A
mainspring fixed on the arbor of the hour wheel is wound up every hour
by means of another toothed wheel riding loose on the same arbor and
driven by a small dynamo, to which the other end of the mainspring is
attached. As soon as the hour wheel has made one revolution (driven
round by the spring), a contact switch is closed whereupon the dynamo
winds up the spring again exactly as the train and fly wind up the
spring in fig. 15. These clocks require a good deal of power, and not
being always trustworthy seem to have gone out of use. A contrivance of
this kind now in use is that patented by F. Hope Jones and G.B. Bowell,
and is represented in fig. 32. A pendulum is driven by the scape-wheel
A, and pallets B B in the usual way. The scape-wheel is driven by
another wheel C which, in turn, is driven by the weighted lever D
supported by click E engaging the ratchet wheel F. This lever is centred
at G and has an extension H at right angles to it. J is an armature of
soft iron pivoted at K and worked by the electromagnet M. D gradually
falls in the act of driving the clock by turning the wheels C and A
until the contact plate on the arm H meets with the contact screw L at
the end of the armature J, thus completing the electrical circuit from
terminal T to terminal T' through the electromagnet M, and through any
number of step-by-step dial movements which may be included in the same
series circuit. The armature is then drawn towards the magnet with rapid
acceleration, carrying the lever D with it. The armature is suddenly
arrested by the poles of the magnet, but the momentum of the lever D
carries it farther, and the click E engages another tooth of the ratchet
F. A quick break of the circuit is thus secured, and the contact at L is
a good one, first because the whole of the energy required to keep the
clock going, or in other words the energy required to raise the lever D
is mechanically transmitted through its surfaces at each operation, and
secondly, owing to the arrangement of the fulcrums at G and K which
secure a rubbing contact. The duration of the contact is just that
necessary to accomplish the work which has to be done, and it is
remarkable that when used to operate large circuits of electrically
propelled dials the duration accommodates itself to their exact
requirements and the varying conditions of battery and self-induction.
The ratchet wheel F is usually mounted loosely upon its arbor and is
connected to the wheel C by means of a spiral spring, which in
conjunction with the back-stop click P maintains the turning force on
the wheelwork at the instant when the lever D is being raised.
[Illustration: FIG. 33.--Hope Jones's Dial-driving Device.]
Electrically driven dials usually consist of a ratchet wheel driven by
an electrically moved pall. Care has to be taken that the pushes of the
pall do not cause the ratchet wheel to be impelled too far. The anchor
escapement of a common grandfather's clock can be made to drive the
works by means of an electromagnet, the pendulum being removed. With a
common anchor escapement the scape-wheel can be driven round by wagging
the anchor to and fro. All then that is necessary is to fix a piece of
iron on the anchor so that its weight pulls the anchor over one way,
while an electromagnet pulls the iron the other. Impulses sent through
the electromagnet will then drive the clock. If the clock is wound up in
the ordinary way the motion will be so much helped that the electric
current has very little to do, and thus may be very feeble. Fig. 33
shows the dial-driving device of Hope Jones's clock. Each time that a
current is sent by the master-clock, the electromagnet B attracts the
pivoted armature C, and when the current ceases the lever D with the
projecting arm E is driven back to its old position by the spring F,
thus driving the wheel A forward one division. G is a back-stop click,
and H, I, fixed stops.
It seems doubtful whether in large towns a number of dials could be
electrically driven from a distance because of the large amount of power
that would have to be transmitted. But for large buildings, such as
hotels, they are excellent. One master-clock in the cellar will drive a
hundred or so placed over the building. The master-clock may itself be
driven by electricity, but it will require the services from time to
time of some one to correct the time. Even this labour may be avoided if
the master-clock is _synchronized_, and as synchronization requires but
a small expenditure of force, it can be done over large areas. Hence the
future of the clock seems to be a series of master-clocks, electrically
driven, and synchronized one with another, in various parts of a city,
from each of which a number of dials in the vicinity are driven.
Electrical synchronization was worked out by Louis Breguet and others,
and a successful system was perfected in England by J.A. Lund. The
leading principle of the best systems is at each hour to cause a pair of
fingers or some equivalent device to close upon the minute hand and put
it exactly to the hour. Other systems are designed to retard or to
accelerate the pendulum, but the former appears the more practical
method. There is probably a future before synchronization which will
enable the services of a clockmaker to be largely dispensed with and
relegate his work merely to keeping the instruments in repair.
_Miscellaneous Clocks._--Some small clocks are made to go for a year.
They have a heavy balance wheel of brass weighing about 2 1b and about
2-1/2 in. in diameter, suspended from a point above its centre by a fine
watch spring about 4 in. long. The crutch engages with the upper part of
the spring, and as the balance wheel swings the pallets are actuated.
The whole clock is but a large watch with a suspended balance wheel,
oscillating once in about 8 seconds. Unless the suspension spring be
compensated for temperature, such clocks gain very much in winter.
An ingenious method of driving a clock by water has been proposed. As
the pendulum oscillates to one side, an arm on it rises and at last
lightly touches a drop of water hanging from a very fine nozzle; this
drop is taken off and carried away by the arm, to be subsequently
removed by adhesion to an escape funnel placed below the arm. Hence at
each double vibration of the pendulum part of the work done by a drop of
water falling through a short distance is communicated to the pendulum,
which is thus kept in motion as long as the water lasts. At this rate a
gallon of water ought to drive the clock for 40 hours. Care of course
must be taken to keep the water in the reservoir at a constant level, so
that the drops formed shall be uniform.
If it were worth while, no doubt the oscillations of a pendulum working
in a vacuum could be maintained by the communication and discharge at
each oscillation of a slight charge of electricity; or again, heat might
at each oscillation be communicated to a thermo-electric junction, and
the resulting current used to drive the pendulum.
The expansions and contractions of metal rods under the influence of the
changes of temperature which take place in the course of each night and
day have also been employed to keep a clock wound up, and if there were
any need for it no doubt a small windmill rotating at the top of a tower
would easily keep a turret clock fully wound, by a simple arrangement
which would gear the going barrel of the clock to the wind vane motion,
whenever the weight had fallen too low, and release it when the winding
up was completed. Even a smoke jack would do the same office for a
kitchen clock.
The methods of driving astronomical telescopes by means of clockwork
will be found in the article TELESCOPE. Measurements of small intervals
of time are performed by means of chronographs which in principle depend
on the use of isochronous vibrating tuning-forks in place of pendulums.
In practice it is needful in most cases that an observer should
intervene in time measurements, although perhaps by means of a revolving
photographic film a transit of the sun might be timed with extraordinary
accuracy. But if the transit of a star across a wire is to be observed,
there is no mode at present in use of doing so except by the use of the
human eye, brain and hand. Hence in all such observations there is an
element of personal error. Unfortunately we cannot apply a microscope to
time as we can to space and make the cycle of events that takes place in
a second last say for five minutes so as to time them truly. By personal
observations the divisions of a second cannot in general be made more
accurately than to 1/10 or 1/15 of a second. The most rapid music player
does not strike a note more than 10 or 12 times in a second. It is only
in case of recurring phenomena that we can make personal observations
more accurate than this by taking the mean of a large number of
observations, and allowing for personal error. For the purpose of
determining longitude at sea accuracy to 1/30 of a second of time would
find the place to about 20 yards. It seems to follow that the extent to
which astronomical clocks can be made accurate, viz. to 1/30 of a second
average variation from their mean daily rate, or one two-and-a-half
millionth of 24 hours, is a degree of accuracy sufficient for present
purposes, and it seems rather doubtful whether mechanical science will
in the case of clocks be likely to reach a much higher figure.
In the 17th century it was a favourite device to make a clock show
sidereal time as well as mean solar time. The length of the sidereal day
is to the mean solar day as .99727 to 1, and various attempts have been
made by trains of wheels to obtain this relation--but all are somewhat
complicated.
_Magical clocks_ are of several kinds. One that was in vogue about 1880
had a bronze figure on the top with outstretched arm holding in its hand
the upper part of the spring of a pendulum, about 10 in. long. The
pendulum had apparently no escapement and the puzzle was how it was
maintained in motion. It was impossible to detect the mystery by the aid
of the eye alone; the truth, however, was that the whole figure swung to
and fro at each oscillation of the pendulum, to an amount of 1/400 of an
inch on the outside rim of the base. A movement of 1/400 of an inch per
half second of time is imperceptible; it would be equivalent to
perception of motion of the minute hand of a clock about 6 in. in
diameter, which is almost impossible. The connexion of the figure to the
anchor of the escapement was very complicated, but clocks of the kind
kept fair time. A straw, poised near the end on a needle and with the
short end united by a thread to the bronze figure, makes the motion
apparent at once and discloses the trick. Another magical clock consists
of two disks of thin sheet glass mounted one close behind the other, one
carrying the minute hand and the other the hour hand. The disks rest on
rollers which rotate and turn them round. The front and back of the
movable disks are covered by other disks of glass surrounded by a frame,
so that the whole looks simply like a single sheet of glass mounted in a
frame, in the centre of which the hands rotate, without any visible
connexion with the works of the clock.
Clocks have been made with a sort of balance wheel consisting of a
thread with a ball at the end which winds backwards and forwards
spirally round a rod. In others a swing or see-saw is attached to the
pendulum, or a ship under canvas is made to oscillate in a heavy sea. In
others the time is measured by the fall of a ball down an inclined
plane, the time of fall being given by the formula t = sqrt(2s/(g sin
a)), where s is the length of the incline and a the inclination. But
friction so modifies the result as to render experiment the only mode of
adjusting such a clock. Sometimes a clock is made to serve as its own
weight, as for instance when a clock shaped like a monkey is allowed to
slide down a rope wound round the going barrel. Or the clock is made of
a cylindrical shape outside and provided with a weighted arm instead of
a going barrel; on being put upon an incline, it rolls down, and the
fall supplies the motive power.
Clocks are frequently provided with chimes moved exactly like musical
boxes, except that the pins in the barrel, instead of flipping musical
combs, raise hammers which fall upon bells. The driving barrel is let
off at suitable intervals. The cuckoo clock is a pretty piece of
mechanism. By the push of a wire given to the body of the bird, it is
bent forward, the wings and tail are raised and the beak opened. At the
same time two weighted bellows measuring about 1 X 2 in. are raised and
successively let drop. These are attached to small wooden organ pipes,
one tuned a fifth above the other, which produce the notes. Phonographs
are also attached to clocks, by which the hours are called instead of
rung.
Clocks are also constructed with conical pendulums. It is a property of
the conical pendulum that if swung round, the time of one complete
revolution is the same as that of the double vibration of a pendulum
equal in length to the vertical distance of the bob of the conical
pendulum below its point of support. It follows that if the driving
force of such a pendulum can be kept constant (as it easily can by an
electric contact which is made at every revolution during which it falls
below a certain point) the clock will keep time; or friction can be
introduced so as to reduce the speed whenever the pendulum flies round
too fast and hence the bob rises. Or again by suitable arrangements the
bob may be made to move in certain curves so as to be isochronous. Plans
of this kind are employed rather to drive telescopes, phonographs and
other machines requiring uniform and steady movement.
Comical and performing clocks were very popular in the 15th and 16th
centuries. One at Basel in Switzerland was arranged so as gradually to
protrude a long tongue as the pendulum vibrated. It is still to be seen
there in the museum. The famous clock at Strassburg, originally
constructed in 1574, remade in 1842, displays a whole series of scenes,
including processions of the apostles and other persons, and a cock that
crows. A fine clock at Venice has two rather stiff bronze giants that
strike the hours.
Clocks with complicated movements representing the positions of the
heavenly bodies and the days of the week and month, allowance being made
for leap year, were once the delight of the curious. Repeating clocks,
which sounded the hours when a string was pulled, were once popular. The
string simply raised the lifting piece and let the clock strike as the
hands would do when they came to the hour. This was of use in the old
days when the only mode of striking a light at night was with a flint
and steel, but lucifer matches and the electric light have rendered
these clocks obsolete.
[Illustration: FIG. 34.--Curve of Variation of daily rate.]
_Testing Clocks._--The average amount by which a clock gains or loses is
called its mean or average daily rate. A large daily rate of error is no
proof that a clock is a bad one, for it might be completely removed by
pendulum adjustment. What is required is that the daily rate shall be
uniform, that is, that the clock shall not be gaining (or losing) more
on one day than on another, or at one period of the same day than at
another. In fig. 34 A B is a curve in which the abscissae represent
intervals of time, the ordinates the number of seconds at any time by
which the clock is wrong. The curve C D is one in which the ordinates
are proportional to the tangents of the angles of inclination of the
curve A B to the axis of x, that is dy/dx. Whenever the line A B is
horizontal, C D cuts the axis of x. In a clock having no variation in
its daily rate the curve A B would become a straight line, though it
might be inclined to the axis of x, and C D, also a straight line, would
be parallel to the axis of x, though it might not coincide with it. In a
clock set to exact time and having no variations of daily rate, both the
curves would be straight lines and would coincide with the axis of x.
The curve C D, known as the curve of variation of daily rate, will
generally be found to follow changes of day and night, and of
temperature, and the fluctuations of the barometer and hygrometer; it is
the curve which reveals the true character of the clock. Hence in
testing a clock two things have to be determined: first, the daily rate
of error, and second, the average variations from that daily rate, in
other words the _irregularities_ of going. To test a clock well six
months' or a year's trial is needed, and it is desirable to have it
subjected to considerable changes of temperature.
The bibliography of horology is very extensive. Among modern works
Lord Grimthorpe's _Rudimentary Treatise on Clocks_, _Watches and
Bells_ (8th edition, London, 1903) is perhaps the most convenient.
Many references to older literature will be found in Thomas Reid's
Treatise on Clock and Watchmaking (1849). (G.; H. H. C.)
_Decorative Aspects._--In art the clock occupies a position of
considerable distinction, and antique examples are prized and collected
as much for the decorative qualities of their cases as for the
excellence of their time-keeping. French and English cabinet-makers have
especially excelled, although in entirely different ways, in the making
of clock cases. The one aimed at comely utility, often made actually
beautiful by fit proportion and the employment of finely grained woods;
the other sought a bold and dazzling splendour in which ornament overlay
material. It was not in either country until the latter part of the 17th
century that the cabinet-maker's opportunity came. The bracket or
chamber clock gave comparatively little scope to the worker in wood--in
its earlier period, indeed, it was almost invariably encased in brass or
other metal; and it was not until the introduction of the long pendulum
swinging in a small space that it became customary to encase clocks in
decorative woodwork. The long or "grandfather" clock dates from about
the fourth quarter of the 17th century--what is, perhaps, the earliest
surviving English dated specimen is inscribed with the date 1681.
Originally it was a development of the dome-shaped bracket clock, and
in the older examples the characteristic dome or canopy is preserved.
The first time-keepers of this type had oaken cases--indeed oak was
never entirely abandoned; but when walnut began to come into favour a
few years later that beautifully marked wood was almost invariably used
for the choicest and most costly specimens. Thus in 1698 the dean and
chapter of St Paul's cathedral paid the then very substantial price of
L14 for an inlaid walnut long-cased eight-day clock to stand in one of
the vestries. The rapidity with which the new style came into use is
suggested by the fact that while very few long clocks can be certainly
dated before 1690, between that year and the end of the century there
are many examples. Throughout the 18th century they were made in myriads
all over England, and since they were a prized possession it is not
surprising that innumerable examples have survived. Vary as they may in
height and girth, in wood and dial, they are all essentially alike. In
their earlier years their faces were usually of brass engraved with
cherubs' heads or conventional designs, but eventually the less rich
white face grew common. There are two varieties--the eight-day and the
thirty-hour. The latter is but little esteemed, notwithstanding that it
is often as decorative as the more expensive clock. The favourite walnut
case of the late 17th and early 18th century gave place in the course of
a generation to mahogany, which retained its primacy until the
introduction of cheaper clocks brought about the supersession of the
long-cased variety. Many of these cases were made in lacquer when that
material was in vogue; satinwood and other costly foreign timbers were
also used for bandings and inlay. The most elegant of the "grandfather"
cases are, however, the narrow-waisted forms of the William and Mary
period in walnut inlay, the head framed in twisted pilasters. Long
clocks of the old type are still made in small numbers and at high
prices; they usually contain chimes. During the later period of their
popularity the heads of long clocks were often filled in with painted
disks representing the moon, by which its course could be followed. Such
conceits as ships moving on waves or time with wings were also in
favour. The northern parts of France likewise produced tall clocks,
usually in oaken cases; those with Louis Quinze shaped panels are often
very decorative. French love of applied ornament was, however, generally
inimical to the rather uncompromising squareness of the English case,
and the great Louis Quinze and Louis Seize cabinetmakers made some
magnificent and monumental clocks, many of which were "long" only as
regards the case, the pendulum being comparatively short, while
sometimes the case acted merely as a pedestal for a bracket-clock fixed
on the top. These pieces were usually mounted very elaborately in gilt
bronze, cast and chased, and French bracket and chamber clocks were
usually of gilded metal or marble, or a combination of the two; this
essentially late 18th-century type still persists. English bracket
clocks contemporary with them were most frequently of simple square or
arched form in mahogany. The "grandfather" case was also made in the Low
Countries, of generous height, very swelling and bulbous.
See F. J. Britten, _Old Clocks and Watches and their Makers_ (2nd
edition, London, 1904); Mathieu Planchon, _L'Horloge, son histoire
retrospective, pittoresque et artistique_ (Paris, 1899). (J. P.-B.)
CLODIA, VIA, an ancient high-road of Italy. Its course, for the first 11
m., was the same as that of the Via Cassia; it then diverged to the
N.N.W. and ran on the W. side of the Lacus Sabatinus, past Forum Clodii
and Blera. At Forum Cassii it may have rejoined the Via Cassia, and it
seems to have taken the same line as the latter as far as Florentia
(Florence). But beyond Florentia, between Luca (Lucca) and Luna, we find
another Forum Clodii, and the Antonine Itinerary gives the route from
Luca to Rome as being by the Via Clodia--wrongly as regards the portion
from Florentia southwards, but perhaps rightly as regards that from Luca
to Florentia. In that case the Clodius whose name the road bears,
possibly C. Clodius Vestalis (c. 43 B.C.), was responsible for the
construction of the first portion and of that from Florentia to Luca
(and Luna), and the founder of the two Fora Clodii. The name seems, in
imperial times, to have to some extent driven out that of the Cassia,
and both roads were administered, with other minor roads, by the same
_curator_.
See Ch. Hulsen in Pauly-Wissowa, _Realencyclopadie_, iv. 63; cf.
CASSIA, VIA. (T. As.)
CLODIUS,[1] PUBLIUS (c. 93-52 B.C.), surnamed PULCHER, Roman politician.
He took part in the third Mithradatic war under his brother-in-law
Lucius Licinius Lucullus, but considering himself treated with
insufficient respect, he stirred up a revolt; another brother-in-law, Q.
Marcius Rex, governor of Cilicia, gave him the command of his fleet, but
he was captured by pirates. On his release he repaired to Syria, where
he nearly lost his life during a mutiny instigated by himself. Returning
to Rome in 65, he prosecuted Catiline for extortion, but was bribed by
him to procure acquittal. There seems no reason to believe that Clodius
was implicated in the Catilinarian conspiracy; indeed, according to
Plutarch (_Cicero_, 29), he rendered Cicero every assistance and acted
as one of his body-guard. The affair of the mysteries of the Bona Dea,
however, caused a breach between Clodius and Cicero in December 62.
Clodius, dressed as a woman (men were not admitted to the mysteries),
entered the house of Caesar, where the mysteries were being celebrated,
in order to carry on an intrigue with Caesar's wife. He was detected and
brought to trial, but escaped condemnation by bribing the jury. Cicero's
violent attacks on this occasion inspired Clodius with the desire for
revenge. On his return from Sicily (where he had been quaestor in 61) he
renounced his patrician rank, and, having with the connivance of Caesar
been adopted by a certain P. Fonteius, was elected tribune of the people
(10th of December 59). His first act was to bring forward certain laws
calculated to secure him the popular favour. Corn, instead of being sold
at a low rate, was to be distributed gratuitously once a month; the
right of taking the omens on a fixed day and (if they were declared
unfavourable) of preventing the assembly of the comitia, possessed by
every magistrate by the terms of the Lex Aelia Fufia, was abolished; the
old clubs or gilds of workmen were re-established; the censors were
forbidden to exclude any citizen from the senate or inflict any
punishment upon him unless he had been publicly accused and condemned.
He then contrived to get rid of Cicero (q.v.) and the younger Cato
(q.v.), who was sent to Cyprus as praetor to take possession of the
island and the royal treasures. Cicero's property was confiscated by
order of Clodius, his house on the Palatine burned down, and its site
put up to auction. It was purchased by Clodius himself, who, not wishing
to appear in the matter, put up some one to bid for him. After the
departure of Caesar for Gaul, Clodius became practically master of Rome
with the aid of armed ruffians and a system of secret societies. In 57
one of the tribunes proposed the recall of Cicero, and Clodius resorted
to force to prevent the passing of the decree, but was foiled by Titus
Annius Milo (q.v.), who brought up an armed band sufficiently strong to
hold him in check. Clodius subsequently attacked the workmen who were
rebuilding Cicero's house at the public cost, assaulted Cicero himself
in the street, and set fire to the house of Q. Cicero. In 56, when
curule aedile, he impeached Milo for public violence (_de vi_), when
defending his house against the attacks of Clodius, and also charged him
with keeping armed bands in his service. Judicial proceedings were
hindered by outbreaks of disturbance, and the matter was finally
dropped. In 53, when Milo was a candidate for the consulship, and
Clodius for the praetorship, the rivals collected armed bands and fights
took place in the streets of Rome, and on the 20th of January 52 Clodius
was slain near Bovillae.
His sister, CLODIA, wife of Q. Caecilius Metellus Celer, was notorious
for her numerous love affairs. It is now generally admitted that she was
the Lesbia of Catullus (Teuffel-Schwabe, _Hist. of Roman Lit._, Eng.
tr., 214, 3). For her intrigue with M. Caelius Rufus, whom she
afterwards pursued with unrelenting hatred and accused of attempting to
poison her, see Cicero, _Pro Caelio_, where she is represented as a
woman of abandoned character.
AUTHORITIES.--Cicero, _Letters_ (ed. Tyrrell and Purser), _Pro Caelio,
pro Sestio, pro Milone, pro Domo sua, de Haruspicum Responsis, in
Pisonem_; Plutarch, _Lucullus, Pompey, Cicero, Caesar_; Dio Cassius
xxxvi. 16, 19, xxxvii. 45, 46, 51, xxxviii. 12-14, xxxix. 6, 11, xl.
48. See also I. Gentile, _Clodio e Cicerone_ (Milan, 1876); E. S.
Beesley, "Cicero and Clodius," in _Fortnightly Review_, v.; G.
Lacour-Gayet, _De P. Clodio Pulchro_ (Paris, 1888), and in _Revue
historique_ (Sept. 1889); H. White, _Cicero, Clodius and Milo_ (New
York, 1900); G. Boissier, _Cicero and his Friends_ (Eng. trans.,
1897).