carrving 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 (when ever the clock is not striking) you may pull up the weight 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. And it would be just the same if you wound up the striking part and its pulley with a key, instead of pulling the string, 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 full as the going part.
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. 14 (in which the same letters are used as in the corresponding parts of fig. 1) 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 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.
Fig. 14.—Harrison's Going-Ratchet.
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 until you lift it, and then 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. In the common construction of this apparatus there is nothing to ensure its being raised high enough to keep in gear the whole time of winding, if the man loiters over it. For this purpose Sir E. Beckett has the arbor of the bolt and shutter made to pump in and out of gear ; and, instead of the Fhutter covering the winding-hole, it ends in a circular arc advanced just far enough to prevent the key or winder from being put on, by obstructing a ring set on the end of the pipe. In order to get the winder on, you must raise the lever high enough for the arc to clear the ring. During the two or three minutes which the clock may take to wind, the arc will be descending again behind the ring, so that now you cannot get the winder off again without also pulling the maintaining power out of gear; so that even if it is constructed to keep in action ten minutes, if required, still it will never remain in action longer than the actual time of winding. The circular arc must be thick enough, or have a projecting flange added to it deep enough, to prevent the winder being put on by merely pushing back the maintaining power lever without lifting it.
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.
Equation Clocks.
It would occupy too much space to describe the various contriv ances for making clocks show the variations of solar compared with mean time (called equation clocks), the days of the month, periods of the moon, and other phenomena. The old day of the month clocks required setting at the end of every month which has not 31 days, and have long been obsolete. Clocks are now made even to provide for leap year. But we doubt whether practically anybody ever takes his day of the month from a clock lace, especially as the figures are too small to be seen except quite near. Several persons have taken patents for methods of exhibiting the time by figures appear ing through a hole in the dial, on the principle of the "numbering machine." But they do not reflect that no such figures, on any practicable scale, are as conspicuous as a pair of hands ; and that nobody really reads the figures on a dial, but judges of the time in a moment from the position of the hands ; for which reason the minute hand should be straight and plain, while the hour hand has a "heart " near the end ; 12 large marks and 48 small ones make a more distinguishable dial than one with figures ; and the smaller the figures are the better, as they only tend to obscure the hands.
Striking Clocks.
There are two kinds of striking work used in clocks. The older of them, 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 that 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 strik ing of any hour may be omitted or repeated without deranging the following ones. In turret clocks there is no occasion for the repeating movement; and for the purpose of describing the other, which is called the locking-plate movement, we may as well refer to fig. 22, which is the front view of a large clock, striking both hours and quarters on this plan. In the hour part (on the left), you observe a bent lever BAH, called the " lifting-piece," of which the end H has just been left off by the snail on the hour-wheel 40 of the going part; and at the other end there are two stops on the back side of the lever, one behind, and rather below the other ; and against the upper one a pin in the end of a short lever 9 B, which is fixed to the arbor of the fly, is now resting, and thereby the train is stopped from running, and the clock from striking any more. The stops are shown on the quarter lifting-piece in the figure (27) of the Westminster clock. We omit the description of the action of the wheels, because it is evident enough. At D may be seen a piece projecting from the lever AB, and dropping into a notch in the wheel 78. That wheel is the locking-wheel or locking-plate ; and it has in reality notches such as D all round it, at distances 2, 3, up to 12, from any given point in the circumference, which may be considered as marked off into 78 spaces, that being the number of blows struck in 12 hours. These notches are shown in the locking-plate of the quarter part in fig. 22, but not in the hour part, foi want of size to show them distinctly.
snail depressing the other end H, a few minutes before the hour, the fly -pin slips past the first of the stops at B, but is stopped by the second and lower one, until the lever is dropped again exactly at the hour. Thus the pin can pass, and would go once round, allowing the train to go on a little; but before it has got once round, AB has been lifted again high enough to carry both stops out of the way of the fly-pin, by means of the cylinder with two slices taken off it, which is set on the arbor of the wheel 90, and on which, the end of the lifting-piece rests, with a small roller to diminish the friction. If the clock has only to strike one, the lifting-piece will then drop again, and the fly-pin will be caught by the first stop, having made (according to the numbers of the teeth given in fig. 22) 5 turns. But if it has to strike more, the locking- wheel comes into action. That wheel turns with the train, being either driven by pinion 20 on the arbor of the great wheel, or by a gathering pallet on the arbor of the second wheel, like G in fig. 15 ; and when once the lifting- piece is lifted out of a notch in the locking-plate, it cannot fall again until another notch has come under the bit D ;
nd as the distance of the notches is proportioned to the