1902 Encyclopedia > Clocks > Church and Turret Clocks

(Part 9)

Clocks (cont.)

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 must 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; an 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, three 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.

Within the last twenty years all the best clockmakers have accordingly adopted the four-legged or three-legged gravity escapement for turret clocks above the smallest size; though inferior ones still persist in using the dead escapement, which is incapable of maintaining a constant rate under a variable state of friction, as has been shown before. When the Astronomer Royal in 1844 laid down the condition for the Windminster clock that it was not to vary more than a second a day, the London Company of Clockmasters pronounced it impossible, an the late Mr Clockmakers pronounced it impossible, and the late Mr Vulliamy, who had been for many years the best maker of large clocks, refused to tender for it at those terms. The introduction of the gravity escapement enabled the largest and coarsest looking clocks with cast-iron wheels and pinions to go for long period with a variation much nearer a second a week than a second a day. And the consequence was that the price for large clocks was reduced to about one-third of what it used to be for an article inferior in performance though more showy in appearance.

Another great alteration, made by the French clockmasters before our, was in the shape and construction of the frame. The old form of turret clock-frame was that of a large iron cage, of which some of the vertical bars take off, and are fitted with brass bushes for the pivots of the wheels to run in; and the wheels of each train, i.e., the striking, the going, and the quarter trains, have their pivots all in the vertical bar belonging to that part. Occasionally they advanced so far as to make the bushes movable, i.e., fixed with screws instead of riveted in, so that one wheel may be taken out without the others. This cage generally stood upon a wooden stool on the floor of the clock room. The French clockmakers long ago saw the objections top this kind of arrangement, and adopted the plan of a horizontal frame or bed, cast all in one piece, and with such smaller frames or cocks set upon it as might be required for such of the wheels as could not be conveniently got on the same level. The accompanying sketch (fig. 19) of the clock of Meanwood church, near Leeds, one of the first on that plan, will sufficiently explain it. All the wheels of the going part, except the great wheel, are set in a separate frame called the movement frame, which is complete in itself, and light enough to take off and carry away entire, so that any cleaning or repairs required in the most delicate part of the work can be done in the clock factory, and the great wheel, barrel, and rope need never the disturbed at all. Even this movement frame is now dispensed with; but we will reserve the description of the still more simple kind of frame in which all the wheels lie on or under the great horizontal bed, until we have described train remontoires.

Train Remontoires

Although the importance of these is lessened by the invention of an effective gravity escapement, they are still occasionally used, and are an essential part of the theory of clockmaking. It was long ago perceived that all the variations of force, except friction of the pallets, might be cut off by making the force of the scape-wheel depend on a small weight or spring wound up at short intervals by t he great clock weight and the train of wheels.

This also has the advantage of giving a sudden and visible motion to the minute hand of those intervals, say of half a minute, when the remontoire work is let off, so that time may be taken from the minute hand of a large public clock as exactly as from the seconds had of an astronomical clock; and besides that, greater accuracy may be obtained in the letting off of the striking part. We believe the first maker of a large clock with a train remontoire was Mr Thomas Reid of Edinburgh, who wrote the article on clocks in the first edition of this Encyclopaedia, which was the afterwards expanded into a well-known book, in which his remontoire was described. The scape-wheel was driven by a small weight hung by a Huyghen’s endless chain, of which one of the pulleys was fixed to the arbor, and the other rode upon the arbor, with the pinion attached to it, and the pinion was driven and the weight wound up by the wheel below (which we will call the third wheel), as follows. Assuming the scape-wheel to turn in a minute, its arbor has a notch cut half through it on opposite sides in two places near to each other; on the arbor of the wheel, which turns in ten minutes, suppose, there is another wheel with 20 spikes sticking out of its rim, but alternately in two different planes, so that one set of spikes can only pass through one of the notches on the scape-wheel arbor, and the other set only through the other. Whenever then the scape-wheel completes a half turn, one spike is let go, and the third wheel is able to move, and with it the whole clock-train and the hands, until the next spike of the other set is stopped by the scape-wheel arbor; at the same time the pinion on that arbor is turned half around, winding up the remontoire weight, but without taking its pressure off the scape-wheel. Reid says that, so long as this apparatyus was kept in good order, the clock went better than it did after it was removed in consequence of its getting out of order from the constant banging of the spikes against the arbor.

The Royal Exchange clock was at first made in 1844 on the same principle, except that, instead of the endless chain, an internal wheel was used, with the spikes set on it externally, which is one of the modes by which an occasional secondary motion may be given to a wheel without disturbing its primary and regular motion. A drawing of the original Exchange clock remonstoire is given in the Rudimentary Treatise on Clocks; but for the reasons which will appear presently, it need not be repeated here, especially as the following is a more simple arrangement of a gravity train remontoire, much m ore frequently used in principle. Let E in fig. 20 be the scape-wheel turning in a minute, and e its pinion, which is driven by the wheel D having a pinion d driven by the wheel C, which we may suppose to turn in an hour. The arbors of the scape-wheel and hour-wheel are distinct, their pivots meeting in a bush fixed somewhere between the wheels. The pivots of the wheel D are set in the frame AP, or on another short arbor between then. The hour-wheel also drives another wheel G, which again drives the pinion f on the arbor which carries the two arms f A, f B; and on the same arbor is set a fly with a ratchet, like a common striking fly, and the numbers of the teeth are so arranged that the fly will turn one for each turn of the scape-wheel. The ends of the remontoire arms f A, f B are capable of alternately passing the notches cut half through the arbor of the scape-wheel, as those notches successively come into the proper position at the end of every half minute; as soon as that happens the hour-wheel raises the movable wheel D and its frame through a small angle; but nevertheless, that wheel keeps pressing on the scape-wheel keeps pressing on the scape-wheel as if it were not moving, the point of contact of the wheel C and the pinion d being the fulcrum or centre of motion of the lever A d P. It will be observed that the remontaire arms f A, f B have springs set on them to diminish the blow on the scape-wheel arbor, as it is desirable not to have fly so large as to make the motion of the train, and consequently of the hands, too slow to be distinct. For the same reason it is not desirable to drive the fly by an endless screw, as was done in most of the French clocks on this principle in the 1851 Exhibition. There is also an enormous loss of force by friction in driving an endless screw, and consequently considerable risk of the clock-stopping either from cold or from wasting of the oil.

Another kind of remontoire is on the principle of one beveled wheel lying between two others at right angles to it. The first of the beveled wheels is driven by the train, and the third is fixed to the arbor of the scape-wheel; and the intermediate beveled wheel, of any size, rides on its arbor at right angles to the other two arbors which are in the same line. The scape-wheel will evidently turn with the same average velocity as the first beveled wheel, though the intermediate one may move up and down at intervals. The transverse arbor which carries it is let off and lifted a little at half-minute intervals, as in the remontoire just now described; and it gradually works down as the scape-wheel turns its pressure, until it is freed again and lifted by the clock train.

In all these gravity remontoires, however, it must have been observed that we only get rid of the friction of the heavy parts of the train and the dial-work, and that the scape-wheel is still subject to the friction of the remontoire wheels, which, though much less than the other, is still something considerable. And accordingly, attempts have frequently been made to drive the scape-wheel by a spiral spring, like the mainspring of a watch. Onf of these was described in the 7th edition of this Encyclopaedia; and Sir G. Airy, a few years ago, invented another on the same principle, of which two or three specimens were made. But it was found, and indeed it ought to have been foreseen, that these contrivances were all defective in the mode of attaching the spring, by making another wheel or pinion ride on the arbor of the spare-wheel, which produced a very mischievous friction, and so only increased the expense of the clock without any corresponding advantage; and the consequence was that spring remontoires, and remontoires in general, had come to be regarded as a mere delusion. It has however now been fully proved that they are not so; for, by a very simple alternation of the previous plans, a spiral spring remontoire amy be made to act with absolutely no friction, except that of the scape-wheel pivots, and the letting-off springs A,B, in ten last drawing. The Meanwood clock (fig. 17) was the first of this kind; but it will be necessary to give a separate view of the remontoire work.

In the next figure (21), A, B, D, E, e, f are the same things as in fig. 20. But e, the scape-wheel pinion, is no longer fixed to the arbor, nor does it ride on the arbor, as has been the case in all the previous spring remontoires, thereby producing probably more friction than was saved in other respects; but it rides on a stud k, which is set in the clock-frame. On the face of the pinion is a plate, of which the only use is to carry a pin h (and consequently its shape is inmaterial), and in front of the plate is set a bush b, with a hole through it, of which half is occupied by the end of the stud k to which the bush is fixed by a small pin, and the other half is the pivot-hole for the scape-wheel arbor. On the arbor is set the remontoire spring s (a moderate-sized musical-box spring is generally used) of which the outer end is bent into a loop to take hold of the pin h. In fact, there are two pins at h, one a little behind the other, to keep the coils of the spring from touching each other. Now, it is evident that the spring may be wound up half or a quarter of a turn at the proper intervals without taking the force off the scape-wheel, and also without affecting, and also without affecting it by any friction whatever, When the scape-wheel turns in a minute, the letting-off would be done as before described, by a couple of notches in the scape-wheel arbor, through which the spikes, A, B, as in fig. 20, would pass alternately. But in clocks with only three wheels in the train it is best to make the scape-wheel turn in two minutes, and consequently you would want four notches and four remontoire arms, and the fly would only make a quarter of a turn. And therefore Sir E. Beckett, who invented this remontoire, made the following provision for diminishing the friction of the letting off work. The fly pinion f has only half the number of teeth of the scape-wheel pinion, being a lantern pinion of 7 or 8, while the other is a leaved pinion of 14 or 16, and therefore the same wheel D will properly drive both, as will be seen hereafter. The scape-wheel arbor ends in a cylinder about 5/8 inch in diameter, with two notches at right angles cut in its face, one of them narrow and deep, and the other broad and shallow, so that a long and thin pin B can pass only through one, and a broad and short pin A through the other. Consequently, at each quarter of a turn of the scape-wheel, the remontoire fly, on which the pins A, B are set on springs, as in fig. 20, can turn half round. It is set on its arbor f by a square ratchet and click, which enables you to adjust the spring to the requisite tension to obtain the proper vibration of the pendulum. A better construction, afterwards introduced, is to make the fly separate form the letting-off arms, whereby the blow on the cylinder is diminished, the fly being allowed to go on as in the gravity escapement. The performance of this is so much more satisfactory than that of the gravity remontoires, that Mr Dent, altered that of the Royal Exchange to a spring one is 1854, which had the effect of reducing the clock-weight by one-third, besides improving the rate of going. It should be observed, however, that even a spring remontoire requires a larger weight than the same clock without one; but as none of that additional force reaches the pendulum, that is of no consequence. The variation of force of the remontoire spring from temperature, as it only affects the pendulum through the medium of the dead escapement, is far too small to produce any appreciable effect; and it is found that clock of this kind, with a compensated pendulum 8 feet long, and of about 2 cwt., will not vary above a second a month, if the pallets are kept clean and well oiled. No turrte clock without either a train remontoire or a gravity escapement will approach that decree of accuracy. The King’s Cross clock, which was the first of this kind, went with a variation of about a second in three weeks in the 1851 exhibition, and has sometimes gone for two months without any discoverable error, though it wants the jeweled pallets which the Exchange clock has. But these clocks require more care than gravity escapement ones, and are certain to be spoilt as soon as they get ignorant or careless hands; and consequently the gravity ones have superseded them.

The introduction of this remontoire led to another very important alteration in the construction of large clocks. Hitherto it had always been considered necessary, with a view to diminish the friction as far as possible, to make the wheels of brass or gun-metal, with the teeth cut in an engine. The French clockmakers had begun to use cast-iron striking parts, and cast-iron wheels had been occasionally used in the going part of inferior clocks for the sake of cheapness; but they had never been used in any clock making pretensions to accuracy before the one just mentioned. In consequence of the success of that, it was determined by the astronomer royal and Mr Denison, who were jointly consulted by the Board of Works about the great Westminster clock in 1852, to alter the original requisition for gun-metal wheels there to cast-iron. Some persons expressed their apprehension of iron wheels rusting; but nothing can be more unfounded, for the non-acting surfaces are always painted, and the acting surfaces oiled. A remarkable proof of the folly of the clockmaker’s denunciation of the cast-iron wheels was afforded at the Royal Exchange the next year. In consequence of the bad ventilation of the clock-room, together with the effects of the London atmosphere, some thin parts of the brass work had become so much corroded that they had to be renewed, and some it was replaced with iron; for all the polished iron and brass work had become as rough as if it had never been polished at all; the only parts of the clock which had not suffered from the damp and the bad air were the painted iron work. The room was also ventilated, with a draught through it, and all the iron work, except acting surfaces, painted. Even in the most favourable positions brass or gun-metal losses it surface long before cast-iron wants repainting.

There is, however, a curious point to be attended to in using cast-iron wheels. They must drive cast-iron pinions, for they will wear out steel. The smaller wheels of the going part may be of brass driving steel pinions; but the whole of the striking wheels and pinions may be of iron. A great deal of nonsense is talked about gun-metal, as if it was necessarily superior to brass. The best gun-metal may be, and is, for wheels which are too thick to hammer; but there is great variety in the quality of gun-metal; it is often unsound, and has hard and soft places; and on the whole, it has no advantage over good brass, when not too thick to be hammered. In clocks made under the pressure of competing tenders, if the brass is likely not to be hammered, the gun metal is quite as likely to be the cheapest and the worst possible, like everything else which is always specified to be "best," as the clockmasters know very well that it is a hundred to one if anybody sees their work that can tell the difference between the best and the worst.

Turret Clocks with Gravity Escapement

Fig. 22 is a front view of a large quarter clock of Sir E. Beckett’s design, with all the wheels on the great horizontal bed, a gravity escapement, and a compensated pendulum. They are made in two sizes, one with the great striking wheels 18 inches wide, and the other 14. The striking is done by cams cast on the great wheels, about 1 1/8 inch broad in the large-sized clocks, which are string enough for an hour bell of thirty cwts., and corresponding quarters. Wire ropes are used, not only because they last longer, if kept greased, but because a sufficient number of coils will go on a barrel of less than half the length that would be required for hemp ropes of the same strength, without overlapping, which it is as well to avoid, if possible, through it is not so injurious to wire ropes as it is to hemp ones. By this means also the striking cams can be put on the great wheel, instead of the second wheel, which saves more in friction than could be imagined by any one who had not tried both. In clocks of the common construction two-thirds of the power is often wasted in friction and in the bad arrangement of the hammer work, and the clock is wearing itself out in doing nothing.

The same number of cams are given here to the quarter as to the hour-striking wheel, rather for the purpose of suggesting the expediency of omitting the 4th quarter, as has been done in many clocksmade from this design. It is of no use to strike ding-dong quarters at the hour, and it nearly doubles the work to be done; and if it is omitted it allows the bells to be larger, and therefore louder, because the 1st quarter bell ought to be an octave above the hour bell, if they are struck at the hour; whereas, if they are not heard together the quarters may be on the 4th and 7th of a peal of eight bells. Moreover, the repetition of the four ding-dongs can give no musical pleasure to any one.

The case is different with the Cambridge and Westminster quarter chimes on 4 bells, and the chime at the hour is the most complete and pleasing of all. It is singular that those beautiful chimes (which are partly attributed to Hande) had been heard by thousands of men scattered all over England for 70 years before any one though of copying them, but since they were introduced by Sir E. Beckett in the great Westminster clocks, on a much larger scale ad with a slight difference in the intervals, they have been copied very extensively, and are already almost as numerous in new clocks as the old-fashioned ding-dong quarters. Properly, as at Cambridge and Westminster, the hour bell should be an octave below the third (or largest but one) quarter bell; but as the interval between the quarters and hour is always considerable, it is practically found that the ear is not offended by a less interval. At Worcester cathedral the great 4 _ ton hour bell is only 1 _ notes below the 50 cwt. Tenor bell of the peal, which is made the fourth quarter bell; and at some other places the quarters are the 2d, 3d, 4th, and 7th of a peal of 8, and the hour bell the 8th. Thereby you get more powerful and altogether better sounding quarters. The quarter bells are the 1st, 2d, 3d, and 6th of a peal of 6—independent of the hour bell; and the following is their arrangement:—

2d {3126, 3213}

3d {1326, 6213} 4th

{1236} 1st

The interval between each successive chime of four should be two or at most two and a half times that between the successive blows. At Cambridge it is three times—decidedly too slow; at Westminster twice, which is rather too fast; at Worcester cathedral and most of the later larger clocks 2 _ times, which sounds the best.

At Cambridge the chimes are set on a barrel which wounds turns twice in the hour, as this table indicates, and which is driven by the great wheel with a great waste of power; the clock is wound up every day. An eight-day clock would require a very heavy weight, and a very much greater strain on the wheels, and they are altogether inexpedient for these quarters on any large scale of bells.

Indeed there is some reason for doubting whether the modern introduction of eight-day clocks is an improvement, where they have to strike at all on large bells. Such clocks hardly ever bring the full sound out of the bells; because, in order to do so, the weights would have to be so heavy, an the clock so large, as to increase the price considerably. A hood bell, even of other ordinary thickness, which is less than in the Westminster bells, requires a hammer of not less than 1/40th of its weight, rising 8 or 9 inches from the bell, to bring out the full sound; and therefore, allowing for the loss by friction, a bell of 30 cwt., which is not an uncommon tenor for a large peal, would require a clock weight of 15 cwt., with a clear fall of 40 feet; and either the Cambridge quarters on a peal of ten, or the Doncaster ones on the 2d, 3d, 4th, and 7th bells of a peal of eight, will require above a ton, according to the usual scale of bells in a ringing peal (which is thinner than the Westminster clock bells). Very few clocks are adapted for such weights as there; and without abundance of strength and great size in all the parts, it would be unsafe to use them. But if the striking parts are made to wind up every day, of course 1/7th of these weights will do; and you may have a more powerful clock in effect, and a safer one to manage, in half the compass, and for much less cost. Churches with such bells as these have always a sexton or some other person belonging to them, and in attendance every day, who can wind up the clock just as well as a clockmaker’s man. The going part always requires a much lighter weight, and may as well go a week, and be in the charge of a clockmaker, where it is possible.

There should be some provision for holding the hammers off the bells while ringing, and at the same time a friction-spring or weight should be brought to bear on the fly arbor, to compensate for the removal of the weight of the hammers; otherwise there is a risk of the train running too fast and being broken when it is stopped.

No particular number of cams is required in the striking wheel; any number form 10 to 20 will do; but when four quarters on two bells are used, the quarter-striking wheel should have half as many cams again as the hour-wheel; for, if not, the rope will go a second time over half of the barrel, as there as 120 blows on each quarter bell in the 12 hours to 78 of the hours, while with the three quarters there are only 72. If the two quarter levers are on the same arbor, there must be two sets of cams, one on each side of the wheel; but one set will do, and the same wheel as the hour-wheel, if they are placed as in fig. 23. The hour-striking lever, it will be seen, is differently shaped, so as to diminish the pressure on its arbor by making it only the difference, instead of the sum, of the pressures at the two points of action. This an be done with the two quarter levers, as shown in the Rudimentary Treatise; but the arrangement involves a good deal of extra work, and as the quarter hammers are always lighter than the hour one, it is hardly worth while to resort to it. The shape of the cams is a matter requiring some attention, but it will be more properly considered when we come to the teeth of wheels. The 4th quarter bell in the Cambridge and Westminster quarters should have two hammers and sets of cams longer then the others, acting alternatively, an account o the quick repetition of the blows.

The fly ratchets should not be made of cast-iron, as they sometimes are by clockmasters who will not use cast-iron wheels on any account, because the teeth get broken off by the chick. This breaking may perhaps be avoided by making the teeth rectangular, like a number if inverted V’s set round a circle, and the click only reaching so far that the face of the tooth which it touches is at right angels to the click; but, as before observed, cast-iron and steel do not work well together.

The hammer of a large clock ought to be left "on the lift," when the clock has done striking, if the first blow is to be struck exactly at the hour, as there are always a good many seconds lost in the train getting into action and raising the hammer. Moreover, when it stops on the lift, the pressure on the stops, and on all the pinions above the great wheel, is only that due to the excess of the power of the clock over the weight of the hammer, and not the full force of the weight, and it is therefore easier for the going part to discharge, and less likely to break the stops.

In fig. 22 the wheel marked 60 in each of the striking parts is a winding wheel on the front end of the barrel, and the winding pinion is numbered 10; a larger pinion will do where the hammer does not exceed 40_; and in small clocks no auxiliary winding wheel is needed. But in that case the locking-plate must be driven by a gathering pallet, or pinion with two teeth, on the arbor of the second wheel, with a spring click to keep it steady. In all cases the hammer shanks and tails should be less than two feet long, if possible; for the shorter they are, the more is lost by the change of inclination for nay given rise from the bell. In some clocks with fixed (not swinging) bells, the hammer0head is set on a double shank embracing the bell, with the pivots, not above it in the French way, which makes the hammer strike at a wrong angle, but on each side of the bell, a little below the top. On this plan less of the rise is lost than in the common mode of fixing. The Westminster clock hammers are all fixed in this way.

The first thing to remark in the going part of fig. 22 is that the hour-wheel which carries the snails for letting off the quarters and striking, is not part of the train leading up to the scape-wheel, but independent, so that the train from the great wheel to the scape-wheel, is one of three wheels only. If it were a dead escapement, instead of a gravity escapement clock, the wheel numbered 96 would be the scape-wheel; and as it turns in 90 seconds, it would require 36 teeth or pins for a 1 _ sec. pendulum which most of these gravity-escapement clocks have ; it is about 6 feet long to the bottom of the bob, which, if sunk just below the floor, brings the clock-frame to a very convenient height. The hour-wheel rides loose on its arbor, or rather the arbor can turn within it, carrying the snails and the regulating hand and the beveled wheel which drives all the dials, and it is fixed to the hour-wheel by means of clamping screws on the edge of a round plate on the arbor just behind it, which turn by hand. In a gravity escapement clock this adjusting work is not really necessary; because you can set the clock by merely lifting the pallets off the scape-wheel, and letting the train run till the hands point right. The regulating hand, you observe, in fig. 22 turns the wrong way; because, where the dial is opposite to the back of the clock, no beveled wheels are wanted, and the arbor leads straight off to the dial. It used to be the fashion to put clocks in the middle of the room, so that the leading-off rod might go straight up to the horizontal beveled wheel in the middle, which drove all the dials. But the clock can be set much more firmly on stone corbels, or on cast-iron brackets built into the wall; and it is not at all necessary for the leading-off rod to be vertical. Provided it is only in a vertical plane parallel to the wall, or the teeth of the beveled wheels adapted to the inclination, the rod may stand as obliquely as you please; and when it does, it ought on no account to be made, as it generally is, with universal joint, but the pivots should go into oblique pivot-holes at the top and bottom. The joints increase the friction considerably, and are of no use whatever, except where the rod is too long to keep itself straight. Where the rod does happen to be in the middle of the room, and there are three or four dials, the two middle of the wheels at each end of it must be a little larger than all the others—both the one in the clock and those of the dial-work; for otherwise the three or four wheels in the middle will meet each other and stick fast.

When the pendulum is very long and heavy, it should be suspended from the wall, unless the clock-frame has some strong support near the middle; but a six-feet pendulum, of not more than two cwt., may be suspended from the clock-frame, provided it is as string as it ought to be fore the general construction of the clock, and supported on corbels or iron beams. It has generally been the practice to hang the pendulum behind the clock-frame; but inasmuch as the rope of the going part may always be thinner than that of the striking part, and that part requires less depth in other respects, a different and more compact plan is adopted in the clocks we are describing. The back pivots of the going wheels run in bushes in an intermediate bar, three or four inches from the back of the frame, joining the two cross bars, of which the ends are dotted in the drawing. The pendulum cock is set on the back frame, and the pendulum hangs within it. And in the gravity escapement clocks there is yet another thin bar—about half way between the back frame and the bar on which the bushes of the wheels are set—the only use of which is to carry the bush of the scape-wheel, which is set behind the fly; the wheel, the fly, and the pallets, or gravity—arms, stand between these two intermediate bars; and the pallet-cock. The beat-pins should be of brass not steel, and no oil put to them, or they are sure to stick. The escapement in fig. 22 is not drawn rightly for the present form of them which is given in fig. 13.

The same general arrangement will serve for a dead escapement clock with or without a train remontaire; only the pendulum will not stand so high, ad the front end of the pallet arbor must be set in a cock like those of the striking flies, on the front bar of the frame. And for a dead escapement, if there are large dials and no remontoire, the pendulum should be longer and heavier than that which is quite sufficient for a gravity escapement. The rod of a wooden pendulum should be as thin as it can conveniently be made, and varnished, to prevent its absorbing moisture.

Dials and Hands

The old established form of dial for turret clock is a sheet of copper made convex, to preserve its shape; and this is just the worst form which could have been contrived for it. For, in the first place, the minute-hand, being necessarily outside of the hour-hand is thrown still farther off the minutes to which it has to point, by the convexity of the dial; and consequently, when it is in any position except nearly vertical, it is impossible to see accurately where it is pointing; and if it is bent enough to avoid this effect of parallax, it looks very ill. Secondly, a convex dial at a considerable height from the ground looks even more convex than it really is, because the lines of sight from the middle and the top of the dial make a smaller angle with the eye than the lines from the middle and the bottom, in proportion to the degree of convexity. The obvious remedy for these defects, is simply to make the dial concave instead of convex. As convex dials look more curved than they are, concave ones look less curved than they are, and in fact might easily be taken for flat ones, though the curvature is exactly the same as usual. Old convex dials are easily altered to concave, and the improvement is very striking where it has been done. There is no reason why the same form should not be adopted in stone, cement, slate, or cast-iron, of which materials dials are sometimes, cement, slate, or cast-iron, of which materials dials are sometimes and properly enough made, with the middle part countersunk for the hour hand, so that the minute-hand may go close to the figures and avoid parallax. When dials are large, copper, or even iron or slate, is quite a useless expense, if the stonework is moderately smooth, as most kinds of stone take and retain plaint very well, and the gilding will stand upon it better than it often does on copper or iron.

The figures are generally made much too large. People have a pattern dial painted; and if the figures are not as long as one-third of the radius, and therefore occupying, wit the minutes, about two-thirds of the whole area of the dial, they fancy they are not large enough to be read at a distance; whereas the fact is, the more the dial is occupied by the figures, the less distinct they are, and the more difficult it is to distinguish the position of the hands, which is what people really want to see, and not to read the figures, which may very well be replaced by twelve large spots. The figures, after all, do not mean what they say, as you read "twenty minutes to" something, when the minute-hand points to VIII. The rule which has been adopted, after various experiments, as the best for the proportions of the dial, is this. Divide the radius into three, and leave the inner two-thirds clear and flat, and of some colour forming a strong contrast to the colour of the hands, black or dark blue if they are gilt, and white if they are black. The figures, if there are any, should occupy the next two-thirds of the remaining third, and the minutes be set in the remainder, near the edge, and with every fifth minute more strongly marked than the rest; and there should not be a rim round the dial of the same colour or gilding as the figures. The worst kind of dial of all are the things called skeleton—dials, which either have no middle except the stonework, forming no contrast to the hands, or else taking special trouble to perplex the spectator by filling up the middle with radiating bars. Where a dial cannot be put without interfering with the architecture, it is much better to have none, as is the case in many cathedrals and large churches, leaving the information to be given by the striking of the hours and quarters. This also will save something, perhaps a good deal, in the size and cost of the clock, and if it is one without a train remontoire or gravity escapement, will enable it to go better. The size of public dials is often very inadequate to their height and the distance at which they are intended to be seen. They ought to be at least 1 foot in diameter for every 10 feet of height above the ground, and more whenever the dial will be seen far off; and this rule ought to be enforced on architects, as they are often not aware of it; and indeed they seldom make proper provisions for the clock or the weights in building a tower, or, in short, know anything about the matter.

The art of illuminating dials cannot be said to be in a satisfactory state. Where there happens to be, as there seldom is, a projecting roof at some little distance below the dial, it may be illuminated by reflection, like that at the Horse Guards—about the only merit which that superstitiously venerated and had clock has; and the same thing may be done in some places by movable lamp reflectors, like those put before shop windows at night, to be turned back against the wall during the day. It has also been proposed to sink the dial within the wall, and illuminate it by jets of gas pointing inwards from a kind of projecting rim, like what is called in church windows a "hood-moulding," carried all round. But it is a great objection to sunk dials, even of less depth than would be required here, that they do not receive light enough by day, and do not get their faces washed by the rain. The common mode of illumination is by making the dials either entirely, or all except the figures and minutes and a ring to carry them of glass, either ground or lined in the inside with linen (paint loses its colour from the gas). The gas is kept always alight, but the clock is made to turn in nearly off and full on at the proper times by a 24 hours wheel, with pins set in it by hand as the length of the day varies. Self-acting apparatus has been applied, but it is somewhat complicated, and an unnecessary expense. But these dials always look very ill by day; and it seems often to be forgotten that dials are wanted much more by day than by night; and also, that the annual expense of lighting 3 or 4 dials far exceeds the interest of the entire cost of any ordinary clock. Sometimes it exceeds the whole cost of the clock annually. The use of white opague glass with black figures is very superior to the common method. It is used in the great Westminster clock dials. It is somewhat of an objection to illuminating large dials from the inside, that it makes it impossible to counterpoise the hands outside, except with very short, and therefore very heavy, counterpoises. And if hands are only counterpoised inside, there is no counterpoise at all the force of the wind, which is then constantly tending to loosen them on the arbor, and that tendency is aggravated by the hand itself pressing on the arbor one way as it ascends, an the other way as it descends; and if a large hand once gets in the smallest degree loose, it becomes rapidly worse by the constant shaking. It is mentioned in Reid’s book that the minute-hand of St Paul’s cathedral, which is above 8 feet long, used to fall over a minute as it passed from the left to the right side of XII, before it was counterpoised outside. In the conditions to be followed in the Westminster clock it was expressly required that "the hands be counterpoised externally, for wind as well as weight." The long hand should be straight and plain, to distinguish it as much as possible from the hour hand, which should end in a "heart" or swell. Many clockmakers and architects, on the contrary, seem to aim at making the hands as like each other as they can; and it is not uncommon to see even the counterpoises gilt, probably with the same object of producing apparent symmetry and the same result of producing real confusion.

The old fashion of having chimes or tunes played by machinery on church bells at certain hours of the day has greatly revived in the last few years, and it has extended to town halls, as also that of having very large clock bells, which had almost become extinct until the making of the Westminster clock. The old kind of chime machinery consisted merely of a large wooden barrel about 2 feet in diameter with pins stuck in it like those of musical box, which pulled down levers that lifted hammers on the bells. Generally there were several tunes "pricked" on the barrel, which had an endway motion acting automatically, so as to make a shift after each tune, and with a special adjustment by hand to make it play a psalm tune on Sundays. But though these tunes were very pleasing and popular in the places where such chimes existed they were generally feeble and irregular, because the pins and levers were not strong enough to lift hammers of sufficient weight for the large bells, and there were no means of regulating the time of dropping off the levers. Probably the last large chime work of this kind was that put up by Dent to play on 16 bells at the Royal Exchange in 1845, with the improvement of a cast-iron barrel and stronger pins than in the old wooden barrels.

A much improved chime machine has been introduced since, at first by an inventor named Imhoff, who sold his patent, or the right to use it, to Messrs Gillett and Bland of Croylon, and also to Messrs Lund and Blockley of Pall Mall, who have both added further improvements of their own. The principle of its is this; instead of the hammers being lifted by the pins which let them off, they are lifted whenever they are down by an independent set of cam wheels of ample strength; and all that the pins on the barrel have to do is to trip them up by a set of comparatively light levers or detents. Consequently the pins are as small as those of a barrel organ, and many more tunes can be set on the same barrel than in the old plan, and besides that, any number of barrels can be kept, and put in form time to time as you please; so that you may have as many tunes as the regulating and adjusting the time, and the machinery is altogether of a very perfect kind for its purpose, but it must be seen to be understood.

It is always necessary in chimes to have at least two hammers to each bell to enable a note to be repeated quickly. Some ambitious musicians determined to try "chords" or double notes struck at once, is spite of warning that they could not be made to strike quite simultaneously, and so it turned out, and it is uselss to attempt them. The largest peals and chimes yet made have been at Worcester cathedral, and the town halls of Bradford and Rochdale, and a still larger one is now making for Manchester, all by Gillett and Bland. The clock at Worcester, which as yet ranks next to Westminster, was made by Mr Joyce of Whitchurch; the others are by Gillett and Bland. At Boston church they have chimes in imitation of some of the foreign ones on above 40 small bells, which were added for that purpose to the eight of the peal; but they are not successful, and it is stated in Sir E. Beckett’s book on clocks and bells, that he warned them that the large and small bells would not harmonize, though either might be used separately. Other persons have attempted chimes on hemispherical bells, like those of house clocks; but they also are a failure for external bells to be heard ay a distance. This however belongs rather to the subject of bells; and we must refer to that book for all practical information about them.

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Clocks - Table of Contents

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