Edmund Beckett

“ An increase of density of the air is equivalent to a diminution of the specific gravity of the pendulum, and that is equivalent to diminution of the force of gravity while the inertia remains the same. And as the velocity of the pendulum varies directly as the force of gravity and inversely as the inertia, an increase of density must diminish the velocity or increase the time. ”

“ 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. ”

“ Gravity escapements require more weight than a direct impulse escapement with an equally fine train; and they try the accuracy of the wheelcutting more severely. If there is a weak place in the train of a common clock the scape-wheel only follows the pendulum more weakly; but in a gravity escapement it always has to raise the pallets, and ought to raise them quickly, and especially in clocks for astronomical purposes where you take its exact time from the sound of the beats, and so the lifting must not lag and sound uneven. ”

“ 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 ”

“ Seeing that a clock at least the going part of it is a machine in which the only work to be done is the over coming 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 every pendulum, that is to say, in every body hung so as to be capable of vibrating freely, there is a certain point, always some where below the centre of gravity, which possesses these remarkable properties that if the pendulum were turned upside down, and set vibrating about this point, it would vibrate in the same time as before, and moreover, that the distance of this point from the point of suspension is exactly the length of that imaginary simple pendulum which would vibrate in the same time. ”

“ A remontoire escapement is one in which the pendulum does not receive its impulse from the scape-wheel, but from some small weight or spring which is lifted or wound up by the scape-wheel at every beat, and the pendulum has nothing to do with the scapewheel except unlocking it. When this impulse is received from a weight the escapement is also called a gravity escapement; and in asmuch as all the remontoire clock escapements that are worth notice have been gravity escapements, we may use that term for them at once. ”

“ A clock which is capable of going accurately must have some contrivance to keep it going while you are winding it 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 Huyghens, 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. ”

“ When you wind up the weight (which is equivalent to taking it off) , the click IV 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. ”

“ It is singular that those beautiful chimes (which are partly attributed to Handel) had been heard by thousands of men scattered all over England for 70 years before any one thought of copying them, but since they were introduced by Sir E. Beckett in the great Westminster clock, on a much larger scale and 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. ”

“ The gas is kept always alight, but the clock is made to turn it nearly off and full on at the proper times by a 24-hour wheel, with pins set in it by hand as the length of the day variew. 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. ”

“ Again, the friction on the dead part of the pallets tends to produce the same effect on the time ; the arc of course it tends to diminish. For in the descent of the pendulum the friction acts against gravity, but in the ascent with gravity, and so shortens the time ; and there is rather less action on the dead part of the pallets in the ascent than in the descent. For these reasons the time of vibration of a pendulum driven by a dead escapement is a little greater than of the same pendulum vibrating the same arc freely ”

“ Spring clocks are generally resorted to for the purpose of saving length ; for as clocks are generally made in England, it is impossible to make a weight-clock capable of going a week, without either a case nearly 4 feet high, or else the weights so heavy as to produce a great pressure and friction on the arbor of the great wheel. ”

“ But in the latter case it is better to have two barrels and great wheels acting on opposite sides of a very strong pinion between them, as it both reduces the strain on the teeth and the friction of the pivot of that pinion. Such clocks sometimes liave a 5 feet or l sec. pendulum, as the case must be a tall one. The great thing is to make the scape-wheel light, and even then you can never get more than a small arc of vibration, which is undesirable for the reason given above, and such a long train is peculiarly sensitive to friction. ”

“ Even in the most favourable positions brass or gun-metal loses its 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 ”

“ A rotary pendulum is kept in motion by the train of the clock ending in a horizontal wheel with a vertical axis, from which pro jects an arm pressing against a spike at the bottom of the pendu lum ; and it has this disadvantage that any inequality in the force of the train, arising from variations of friction or any other cause, is immediately transmitted to the pendulum ; whereas it will be seen that in several kinds of escapements which can be applied to a vibrating pendulum, the variations of force can be rendered nearly or quiteinsensible. ”

“ 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 be disturbed at all. ”

“ Mr Ritchie of Edinburgh, however, has combined the principle of Bain's and Jones's clocks in a manner which is testified to be completely successful in enabling one standard clock to control and keep going any number of subordinate ones, which do not require winding up as Jones's do, but are driven entirely by their pendulums. This differs from Wheatstone's plan in this, that his subordinate clocks had no pendulum swinging naturally and only wanting its vibrations helping a little, but the pallets had to be made to vibrate solely by the electrical force. ”

“ 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 from 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 only noise made in striking is their running on over their ratchets when the striking stops. Each striking weight is a ton and a half or was before the great hammer was reduced. They take 5 hours to wind up, and it has to be done twice a week, which was thought better than making the parts larger and the teeth more numerous and the weights twice as much, to go a week, and of course the winding must have taken twice as long, as it was adapted to what a man can do continuously for some hours. Con- sequently it was necessary to contrive something to stop the man. ”

“ Such pendulums are used where a continuous instead of an intermittent motion of the clock train is required, as in the clocks for keeping an equatorial telescope directed to a star, by driving it the opposite way to the motion of the earth, to whose axis the axis on which the telescope turns is made parallel. Clocks with such pendulums may also be used in bedrooms by persons who cannot bear the ticking of a common clock. The pendulum, instead of being hung by a flat spring, is hung by a thin piece of piano-forte wire ”

“ The American clocks prove that they are not too expensive to be used with advantage when properly made ; although, so long as there are no manufactories of clocks here as there are in America, it may be cheaper to make pinions in the slovenly way of cutting off all the ribs of a piece of pinion wire, so as to reduce it to a pinion a quarter of an inch wide, and an arbor 2 or 3 inches long. ”

“ In large clocks with a train remontoire, or even with a gravity escapement, it is hardly safe to use a spring going barrel, because is very likely to be exhausted too much to wind up the remon toire, or raise the gravity pallets, before the winding is finished, if t takes more than two or three minutes ; whereas, with the common escapements, the wheel has only to escape, as the pendulum will keep itself going for some time without any impulse. ”

“ The escapement is that part of the clock in which the rotary motion of the wheels is converted into the vibratory motion of the balance or pendulum, which by some contrivance or other is made to let one tooth of the quickest wheel in the train escape at each vibration ”

“ 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 clocks 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 turret clock without either a train remontoire or a gravity escapement will approach that decree of accuracy. ”

“ It is astonishing how, by continually making one machine after another, with a little deviation each time, the thing gradually assumes a form in which you can hardly recognise your original design at all. ”

“ At Cambridge the chimes are set on a barrel which 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 arc alto gether inexpedient for these quarters on any large scale of bells. ”

“ The success of the Westminster clock pendulum, however, and of smaller zinc and steel pendulums at Greenwich and elsewhere, has established the conclusion that it is unnecessary to incur the expense of a heavy mercurial pendulum, which has become more serious from the great rise in the price of mercury and the admitted necessity for much heavier bobs than were once thought sufficient for astronomical clocks. ”

“ The complete calculation for a compen sated pendulum in which the rods and tubes form any considerable proportion of the whole weight, as they must in a zinc pendulum, is too complicated to be worth undertaking generally, especially as it is always necessary to adjust them finally by trial, and for that purpose the tubes should be made at first a little longer than they ought to be by calculation, except where one is exactly copying pendulums previously tried. ”

“ It is of great importance that the spring should be of uniform thickness throughout its breadth ; and the bottom of the chops which carry it should be exactly horizontal ; otherwise the pendulum will swing with a twist, as they may he often seen to do in ill-made clocks. If the bottom of the chops is left sharp, where they clip the spring, it is very likely to break there ”