Part 8

In the first place, it is necessary to say that Turret Clocks are not merely house clocks upon an enlarged scale, differing from the latter merely in size and weight, but that the extra strength of the machinery requires greater weight of materials 'in a ratio as much higher as the cube is higher than the square of any of its dimensions,' and that increased weight means increase of friction. Besides this point which is peculiarly the province of the Turret Clockmaker, there are important questions to be considered by architects and their employers as to the proper method of constructing a Turret Clock chamber, so as to prevent too much atmospheric variation,--heat and cold, wind and damp, being each likely in some degree, as the seasons change, to affect the public time-keeper,--as witness the clock of St Paul's Cathedral, popularly believed to be an exemplary piece of mechanism, and yet often forced by the wind to vary its time so as to damage its own reputation among those who narrowly watch its behaviour under what may be called trying circumstances. It is not wise to build a tower without careful consideration for the tenant which is to occupy it, or having regard merely to architectural notions of external proportion, for usually it happens that when clock and bells occur as an afterthought, there is often some difficulty and extra expense in planning the room for them. Plenty of length and breadth to allow of the proper fall of the clock-weights and the swing of the pendulum save much in the cost of fixing, and are necessary to secure good time-keeping with the least trouble, for it is obvious that where numerous bevelled wheels with rod-work are employed for the purpose of moving the hands over the dial, if the probabilities of unvarying accuracy are not lessened, the cost must be much increased. Works which have to be placed at some distance from the dials must be more powerful than if they could be put in their proper place, and a little forethought in the architect will save much money both in the original price of the machinery of a clock and in its subsequent repair. Then again, there is always the question for and against the illumination of dials to be considered, and of course with this is unavoidably mixed up not only the arrangements as regards space for the proper working of the time-keeping, striking, and lighting machinery, but the vexed question of ventilation above referred to,--some horologers asserting that chambers as nearly air tight as may be should be devised, and others that there ought to be a draught through the clock-room. There are in fact so many opinions more or less excellent, according to the circumstances of each case, that there is no laying down any arbitrary and unvarying rule, much must be left to the discretion of the Turret Clock manufacturer,--upon whom as has been already stated it is necessary also to rely for the essentials of a good clock, viz., the soundness of the materials, the quality of the workmanship, and the scientific accuracy with which the instrument has been planned and put together. Now before considering the present advanced state of the art of Turret Clockmaking and the various improvements which have to be carefully studied and applied by the makers who would bear the highest reputations as manufacturers, it will be necessary to bear in mind what has been said of the step-by-step progress in horological science of which we have already endeavoured to give the chief particulars. From 1288 A.D., the date of the oldest historical clock--that mentioned as having been set up near Westminster Hall by means of funds derived from a fine levied by the Lord Chief Justice of the period--till now when Big Ben reigns in its stead, is a long interval, with many wonderful incidents, and some great historical names. Henry de Wyck's Paris invention, Galileo's discovery of the pendulum, Huygens's practical application of that discovery, Dr Hooke's 'anchor' escapement, and Graham's dead-beat escapement, Harrison's 'gridiron' pendulum, and the latest applications of electricity and eccentricity, have each and all their peculiar attraction for horological students, but we need not recur to these branches of this highly interesting subject elsewhere treated of. We will proceed to mention a few memoranda about several old public clocks whose ingenious mechanism gained for them a well-deserved fame,--not, perhaps, so much for accuracy in time-keeping as for the grotesque devices with which old clockmakers amused their contemporaries? To them time, as such, was perhaps of not so much consequence as it is to us in these days of telegraph and steam communication. We moderns seem to think it a task sufficiently difficult to set up a sound public time-piece without connecting therewith the wonder-working machinery of a wax-work exhibition.

The CLOCK AT WELLS CATHEDRAL, made originally A.D. 1340, by a monk named Peter Lightfoot, is one of the best known of its class still in some sort of working order. The dial of this horologe is divided into 24 hours; it shows the motion of the sun and moon, and bears upon its summit eight armed knights on horseback, tilting with lance in rest at one another, by a double rotatory motion. This clock was removed from Glastonbury to Wells after the dissolution of the Glastonbury Monastery. In 1835 the works were so worn away that they were replaced by a new train, the curious old dial and equestrian knights being still retained.

+----------------------------------------------------------------------+ | [Illustration: Wells Cathedral Clock.] | +----------------------------------------------------------------------+

ST DUNSTAN'S CLOCK [see p. 137]. This Clock, when old St Dunstan's Church in Fleet Street was pulled down, was sold by public auction, and bought by the late Marquis of Hertford, for whom Decimus Burton the architect erected St Dunstan's Villa in the Regent's Park. In the grounds of that villa this old clock with its automaton giants striking the hours and quarters was put up, and it is there still, to be seen in full working order, performing the same duties as of yore in Fleet Street.

ST JAMES'S PALACE CLOCK [see p. 138] is one of the most ancient public time-pieces now in use, but is intended soon to be removed it is said to South Kensington Museum. It has a locking-plate with ting-tang quarter, the quarter hammers being raised from the pin wheel while the striking hammer is lifted from the pins in the main wheel. It has a crown-wheel escapement with teeth on its edge, and the pallets working upright instead of over the top like a verge escapement. The hands are connected by the bevel wheels below the clock. The whole of the going train with the intermediate and bevel wheels are attached to the one bar so that the whole of the works have to be removed if one piece requires alteration or renewal. The pendulum rod is of iron.

+----------------------------------------------------------------------+ | [Illustration: St Dunstan's Clock.] | +----------------------------------------------------------------------+

ST PAUL'S CATHEDRAL CLOCK [see p. 140] is one of the best examples of old-fashioned clocks in London; it occupies the clock-room in the south-western tower. It may be described as a ting-tang quarter on the rack principle, having hammers raised from pins in the main wheel as in St James's Palace Clock. The train is run in a bar, so that to get away one piece the rest must be disturbed. The escapement is a recoil, beating two seconds with a wood rod pendulum. The length of the minute hand is eight feet, and its weight 75lb; the length of the hour hand is five feet five inches, and its weight 44lb. The diameter of the bell, made from old 'Great Tom of Westminster,' is about 10 feet, its weight 11,474lb; the hammer weighs 145lb, and the clapper 180lb.

+----------------------------------------------------------------------+ | [Illustration: St James's Palace Clock.] | +----------------------------------------------------------------------+

The OLD CLOCK AT THE ROYAL FREE HOSPITAL, GRAY'S INN LANE, is a fair specimen of the work of 120 years ago. It has a recoil escapement, most of the wheels are of wrought-iron, cut by hand, as is also the pinion. The pendulum rod is of iron with leaden bob.

THE WHEELS.

+----------------------------------------------------------------------+ | [Illustration: St Paul's Cathedral Clock.] | +----------------------------------------------------------------------+

And now, in order to form a judgment of what is necessary to be done to make a really sound and valuable Turret Clock of the present day, let me describe the materials of which it should be formed. One of the most important parts of a clock is the wheel-work. Iron wheels are of course very much cheaper than those which are made of gun metal or hard brass, but iron wheels, however well they may sometimes wear, are more liable to oxidize and to decay, and although it is certain that a large number of clocks are constructed with iron wheels by London houses of some reputation, a few years are generally sufficient to prove such time-pieces to be very faulty, and to necessitate the substitution of wheels of the superior metal.

+----------------------------------------------------------------------+ | [Illustration: Old Clock at the Royal Free Hospital.] | +----------------------------------------------------------------------+

The best clocks are usually made with wheels of the best gun metal. The teeth are cut by steam power, with an improved cutting engine; and at the same moment that the teeth are cut, they are finished by the engine without the aid of the file, sand-paper, or other polishing materials, so that the most minute difference cannot possibly occur, their accuracy being secured even to the thousandth part of an inch. In the old times this work was done by a man turning a fly-wheel, but that method necessarily occasioned an unevenness of cut which had afterwards to be removed by filing and hand polishing. Wheels thus made could not of course have that precision of movement which is essential in a public clock, and which can only be obtained by a perfect mechanical fit of the teeth of the wheels, such true mechanical fitting being only secured by truly accurate cutting machines. Hand cutting varies with each artisan, and therefore cannot be equally trustworthy. In cheap clocks, constructed to suit public companies who give their contract to the lowest tender, iron is frequently used instead of steel, both in the pinions and arbors, and cast-iron takes the place of gun metal or hard brass in the wheels and bosses,--the result usually being that the Public Clock gets into disrepute through its requiring to be repaired so frequently, and more money is expended upon such repairs than would have sufficed for the purchase of a thoroughly perfect time-keeper. It is urged by the advocates of iron wheels that a clock can be manufactured at a considerably less cost by their employment, but in estimating expense there seems to have been overlooked the important question, as to what will be the probable durability of the machine.

I should be sorry to condemn wholesale all clocks, the main wheels of which are made of iron, but very certain it is that a large proportion of clocks constructed of this material and by London houses of great reputation (despite of their possessing an escapement invented by amateurs who consider themselves the depositories of all horological knowledge), have been found most faulty time-keepers, and after a few years have become entirely worn out and useless.

It is argued (and rightly so) by the advocates of iron wheels that case-hardened pinions should not be used, in consequence of their wearing with great unevenness, but such persons should be reminded that this objection is much greater in the instance of cast-iron wheels. A case came under my notice some time since of a clock made by a London house, with iron wheels, which after comparatively little time became entirely worn out and had to be removed, a result not at all surprising to those who are aware of the porous nature of iron. The TEETH OF WHEELS have to be made with the greatest skill and care in order that the entire mechanism shall work without friction, and shall not only temporarily keep time with regularity, but shall last for many years without renewal. Teeth should fit into one another without a squeezing pressure (which is equivalent to friction), but with exact uniformity of contact, the action being almost entirely between the teeth separating from each other and not between those which are approaching, i.e. in technical language, the action should be after the line of centres of the wheels and not before it.

Church clocks were accustomed formerly to be made to go for thirty-four hours, and to be wound up every day; by the frequency of which winding the clock could be made to keep time with great accuracy, for regulating could be attended to as frequently, and no great variation could well occur in twenty-four hours. But the regulating, as a matter of course, requires a regulator, or standard, of time, which is not always to be found in country places, nor even is the man in charge of clock-winding always in possession of a watch sufficiently accurate to convey the time from the regulator if there were one to the Church clock. Of late, Church clocks are made to go eight days, and so the labour of frequent winding has been saved, while at the same time by extra care in the manufacture and fixing of a clock, there need be no necessity for frequently regulating it.

PENDULUMS.

Whether the credit of practically applying the mathematical theory and properties of the pendulum was or was not due to Huygens the Dutchman, we have seen that Harris, a London clockmaker, put up the first pendulum clock in St Paul's Church, Covent Garden, in 1621. The great advance upon this discovery was that the pendulum bob must move not in a circle but a cycloid; and that back and front should be alike both in weight and shape to secure regular vibration. Cylindrical bobs are now in general use for large clocks. The old iron rod pendulums were soon discovered to be affected considerably by variations of heat and cold,--the difference between winter and summer being ascertained to amount to the loss of a minute a week. Harrison's gridiron pendulum was one of the chief endeavours to prevent such variation, followed after a long interval by other ingenious inventions, which gained temporary approval and gradually fell into disuse. Room should be provided by the architect of every clock-tower in the chamber below that containing the movement, to allow of the swing of a 15-foot pendulum.

FALL OF THE WEIGHTS.

We have seen that the position in which a clock is placed in regard to the dial or dials whose hands it is to drive is a matter requiring some attention. Properly the floor of the clock-chamber should be so planned that the clock might stand immediately behind, and level with the dials; for there is extra expense and inconvenience connected with any more distant situation of the works,--the fall of the weights being sometimes difficult in such case to be provided for. The weights should hang, wherever it is possible so to arrange, immediately from the barrel to which they are affixed, without the intervention of pulleys of any kind, and much expense may be saved by providing for the descent of the weights to a considerable depth below the clock-chamber. As an instance however of the extent to which such difficulties can be overcome, I may mention that the hands of my great clock at the International Exhibition were situated nearly 400 feet from the clockworks, while the weights were carried by iron wire ropes over pulleys below the floor to a distance of 200 feet from the movement, then over another pulley fixed at a height of 80 feet from the ground.

The ESCAPEMENT is perhaps the most important part of a clock.

CROWN-WHEEL ESCAPEMENT.

+----------------------------------------------------------------------+ | [Illustration: Escapement.] | +----------------------------------------------------------------------+

This is the earliest known escapement, and is to be found, as we have said, in Henry de Wyck's clock, all the difference between his escapement and the above being that one of the weights in de Wyck's balance is now set in a vertical instead of a horizontal plane. The bent end or fork seen in the illustration connects the pendulum with that arm technically called the crutch.

THE ANCHOR ESCAPEMENT.

After the crown-wheel escapement, the anchor escapement, invented by Dr Hooke or one of his contemporaries, came into general use, and remains so still; but it is not generally applied to those clocks which are required to go with the nicest accuracy.

+----------------------------------------------------------------------+ | [Illustration: Anchor Escapement.] | +----------------------------------------------------------------------+

In the next illustration the tooth is seen escaping from the left pallet at the moment of the right pallet's infringing upon the opposite tooth, the pendulum is therefore to be seen still rising a little to the left, and will thus cause the wheel to recoil a little; upon its return the pallet and pendulum are again urged to the right, and so the impulse is continued which is necessary to maintain the motion.

THE DEAD-BEAT ESCAPEMENT.

invented by Graham is the one in most general use for the best clocks made by London makers of the highest repute.

+----------------------------------------------------------------------+ | [Illustration: Dead-beat Escapement] | +----------------------------------------------------------------------+

FRENCH SINGLE-PIN ESCAPEMENT.

This is a simple and ingenious escapement (see next page), which after being used for some time in both France and England went out of use, when, but recently, it was re-invented by a London watch-maker. The teeth are pins of steel set in the face of the wheel, and the upper half of each cylinder cut off as well as a small portion of the under or acting side. This escapement has one great advantage--that if a pin becomes worn or injured it is easily replaced, whereas in a wheel, if one tooth is damaged the wheel itself is worthless.

+----------------------------------------------------------------------+ | [Illustration: French Single-Pin Escapement.] | +----------------------------------------------------------------------+

THREE-LEGG'D GRAVITY ESCAPEMENT.

+----------------------------------------------------------------------+ | [Illustration: Another.] | +----------------------------------------------------------------------+

The above illustration represents a regulator escapement as it would appear in a front view; the pallets are lifted by the three central pins. The locking teeth vary in size from one to nearly two inches. The horizontal pieces projecting from the top of the pallets form the adjustment for the arc of the pendulum.

The great advantages possessed by this escapement over all other gravity escapements, &c., are as follows:--

1. It requires no oil.

2. The angle of the detent planes reduces the friction to almost nil.

3. As the impulse and the unlocking are in one direction, the escapement is unlocked without recoil of impulse arms.

4. No impending force to the pendulum from inertia of impulse arms.

5. The hold in the stops can be increased or diminished to any practical extent by reason of the inverted impulse arms.

6. Less affected by any disturbing forces of the train in proportion to the pressure on the stops.

7. Will bear more weight and give more power to the train without increasing the arc of oscillation.

8. No possibility of tripping under any increase of motive power.

9. The minimum arc of vibration to unlock is 8-tenths of a degree. Other escapements of similar construction require from 4° to 7°.

10. Take less weight for the motive power in proportion to the difference of pressure and draught on the lockings.

11. Unlocks by gravitation instead of by the pendulum and at the time of impulse.

12. Requires no fly nor remontoir, and thus reduces the weight of the motive power by one half.

13. The impulse giving motion to the pendulum increases as the force of gravity on the pendulum decreases. A great advantage over those escapements in which the unlocking is done by the pendulum when its momentum is nearly expended and at the extremity of its arc of vibration.

14. The angle of the detent planes can be set so as not only to offer no resistance to the unlocking, but to give an actual impulse in the same manner as the impulse pallets of a dead escapement. This completely frees the impulse which gives motion to the pendulum from any retarding influence of the train.

15. The arc of vibration is more equal in this than in any other gravity escapement.

16. It is not so liable to stop in consequence of a diminution of arc from the variation of motive force in train.

17. It will answer for regulators as well as for turret clocks, its arc of vibration being from 1° to 3°.

DOUBLE THREE-LEGG'D ESCAPEMENT.

+----------------------------------------------------------------------+ | [Illustration: Double Three-legg'd Gravity Escapement.] | +----------------------------------------------------------------------+

This escapement is chiefly designed for turret clocks with heavy dial-work requiring much power on the scape-wheel. The peculiarity consists of two locking wheels with one set of lifting pins between them. The wheels are set so that the pallets may lie between, and the pallets fall with the pendulum clear of all other contact. The pallet D for instance has its stop in front for the wheel A B C to act upon, and the E stop is acted upon only by _a b c_, the E and A being on different planes. In this escapement, by making the teeth longer and the pallets shorter, the resistance of the pendulum is much reduced, and the stride of the pallets being wider, the actual weight required of them is considerably lessened,--a point of some importance.

THE REMONTOIRE.

is an invention which, being derived from the French, still bears its French title, and consists of either a train remontoire, or a gravity or remontoire escapement, in which latter the impulse is not given to the pendulum directly by the clock-train or weight, but by some small weight lifted up or a small spring bent up by the clock-train at every beat of the pendulum, so as to secure a uniform and constant impulse, the remontoire weights being lifted either faster or slower according to need. The train remontoire differs from the escapement but slightly, the chief difference being that the small weight or spring which gives the impulse to the pendulum is not wound up at every beat, but at some larger interval, seldom more than half a minute. Its effect is to counteract the various errors to which large clocks driving heavy hands are always liable, and to diminish the friction which arises from the use of heavy weights--these being in very large clocks almost incredibly heavy; for instance, the weights used by me for my clock in the Great International Exhibition of 1862 amounted to more than two tons. Whatever the cause of inequality of movement in the clock, whether it be dust or dirt, or insufficient oil, or whether it be wind delaying or expediting the progress of the hands on the dial, the remontoire regulates and counteracts.

THE DIALS.