Pendulum clock

“ But to get an idea is one thing and to apply it is quite another. Pendulums were very complicated mechanisms. In the first place the length of the pendulum decides, you see, the rate of the clock's vibration; a short one resulting in a quick, nervous tick; and a long one in a slow, quiet one. Therefore pendulums meant more even vibration and more accurate time-keeping, and it was just when makers were rejoicing over these advantages that it was discovered the temperature of the place in which a clock stood affected the rod the bob hung on and threw the whole timepiece out of adjustment. ”

“ But the rod of a pendulum clock is never exposed to the heat of the summer sun, nor ever acquires a heat equal to that of the external parts of a human body; and, therefore, though the 3 feet rod of a pendulum clock will indeed be a little longer in the summer than in the winter season, yet the difference will scarcely amount to 1⁄4 line. ”

“ By taking in all the sources of error of higher orders, it has been possible to calculate a pendulum so accurately that, when the clock is loaded with the weight sufficient to give the pendulum the arc of swing for which it is designed, a rate of error has been produced of only half a minute in a year. ”

“ The great weights necessary to drive so large a clock, and which by the friction they would cause might prejudicially influence its performance, are in this case not allowed to act directly upon the pendulum, but are made to wind up a small auxiliary weight once every half-minute, and this weight imparts an exactly uniform impulse to the pendulum at each vibration. This arrangement, which is called the remontoir, is supplemented in this clock by a double lever escapement of a novel kind, in connection with that known as Graham's Dead Beat. ”

“ The same admirable invention of the pendulum affords a means of subdividing time to an almost unlimited nicety. A clock is nothing more than a piece of mechanism for counting the oscillations of a pendulum; and by that peculiar property of the pendulum, that one vibration commences exactly where the last terminates, no part of time is lost or gained in the juxta-position of the units so counted, so that the precise fractional part of a day can be ascertained which each such unit measures. ”

“ Reid and Dennison have written enough to convince the most skeptical that the clock is an old invention. It is not important to us who invented the pendulum, or this or that escapement, but who makes the best pendulum, the best escapement, the most perfect train of wheels and pinions. ”

“ 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. ”

“ Figure 4.—The direct use of a clock to measure the force of gravity was found to be limited in accuracy by the necessary mechanical connection of the pendulum to the clock, and by the unavoidable difference between the characteristics of a clock pendulum and those of a theoretical (usually called “simple”) pendulum, in which the mass is concentrated in the bob, and the supporting rod is weightless.
After 1735, the clock was used only to time the swing of a detached pendulum, by the method of “coincidences.” ”

“ A common clock is merely a pendulum, with wheel-work attached to it, to record the number of the vibrations; and with a weight or spring, having force enough to counteract the retarding effects of friction and the resistance of the air. The wheels show how many swings or beats of the pendulum have taken place, because at every beat, a tooth of the last wheel is allowed to pass. Now, if this wheel has sixty teeth, as is common, it will just turn round once for sixty beats of the pendulum, or seconds ”

“ The pendulum therefore is hung on a piece of steel spring on a separate hook, which lets it go backwards and forwards and carries the weight easily, while a rod projecting from the anchor has a pin, which works in a slot on the pendulum. The pendulum is therefore able to control and regulate the movements of the escapement, and thus the time of the clock. ”

“ The ball swings back and forward rather like a pendulum, as you see, but it does not keep time. The short swings at the end are made much more quickly than the long ones at the beginning. But when we swing a pendulum and let its swings die down there is no such quickening, and hence the usefulness of a pendulum in regulating clocks, and the usefulness of a clock is to tell people like lecturers to stop talking after a reasonable time, before you are thoroughly sick of them and their gravity and levity both. ”

“ His invention has never ceased to be of use to every one. The pendulum was attached to the works of a clock, and has from that moment continued the chief means of measuring time. It rules every family, directs the business of cities, and tells when to go to school and when school is out. The great clock in the City Hall and the clocks in all the steeples and towers are guided by Galileo's pendulum. The wooden clock we buy for two or three dollars, and the costly French clock that ticks on the mantel, owe their chief value to the invention of the young student. ”

“ Those interested in the improvement of clocks are constantly striving after light action and small driving weights. Conversely, the inferior clock has a heavy weight and ticks loud. The “gravity escapement” and others giving a “free” pendulum action would require too much space here, so we must be satisfied with the few successful ones shown out of hundreds of inventions, dozens of them patented. The pendulum stands at the top as a time measurer and was known to the ancients for measuring short periods of time just as musicians now use the metronome to get regular beats. ”

“ Certainly Fromanteel did a vast service to English clockmaking when he brought this solution of the pendulum problem to London, for with the anchor, or dead-beat escapement, combined with a long pendulum terminating in a heavy bob, the force of gravity caused such slight variation that the motion was practically harmonic and had only a very minor effect on the clock. For a long case, you see, has an exceedingly confined arc of oscillation because the swing of the pendulum is so limited. ”

“ But if the notched brass could be turned into a ring, and the pendulum be made to count the notches off for itself, round and round again continuously, registering each revolution as it was completed for future reference, the observer would attain the same result without expending any personal trouble about it. It is this magical conversion of brass and iron into almost intelligent counters of the pendulum's vibrations, that the clock-maker effects by his beautiful mechanism. ”

“ 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 clock consists of a pendulum, the bob of which vibrates between the poles of two permanent magnets, the opposite poles of which face one another. A small platinum-ball is affixed to the upper part of a small brass stem, which is free for lateral motion, being fastened below to a light spindle carried by the upper part of the pendulum-rod. ”

“ At length brass pendulums which, they discovered, made the most trouble, were replaced by those of iron or lead which, being of softer material, expanded and contracted more readily. In our day you will sometimes see a very finely adjusted astronomical clock whose pendulum terminates in a hollow glass or iron receptacle filled with mercury, instead of the usual metal bob. ”

“ A pendulum of the right length in London would lose two and one quarter minutes a day at the equator. The pendulum that vibrates from c to b in two seconds must be four times the length of a one-second pendulum. The pendulum of the great clock at Westminster moves once in two seconds. It is nearly fifteen feet long, and it weighs seven hundred pounds—the heaviest in the world. The heavier and longer the pendulum, the more regularly will the clock move. ”

“ The tendency at present is for large instruments very distinctly toward a motor-driven mechanism operating on the right ascension axis, and governed in one of a considerable variety of ways by an actual clock pendulum. For smaller instruments the old mechanical clock, often fitted with electric brake gear and now and then pendulum regulated, is capable of very excellent work. ”

“ When a Vernier pendulum, vibrating once in ·9 second, or 10 times in 9 seconds, is employed, its coincidences with the seconds pendulum of the clock may be determined to a single vibration with the greatest ease by the unassisted eye, and thus, of course, tenths of a second are readily estimated. ”

“ Turning the handle one way raises the arm, and with that lengthens the acting length of the pendulum spring, and turning the other way, lowers it and shortens the pendulum, but so slightly that it takes fifteen minutes of the quickened rate of the pendulum, when shortened, to add the required 0·3 seconds to the indications of the clock. ”

“ In practice, however, it is found better not to make the contact by springs, which, however light, disturb the pendulum a little, but by a wheel in the train making and breaking contact at every beat; and if the clock has a gravity escapement there is no danger of this friction affecting the pendulum at all. ”

“ At each blow of the pins against the pendulum a “tick” is made, at each blow of a pin against the ratchet a “tock” is sounded, so that as it114 moves the pendulum makes the “tick-tock” sound with which we are all familiar.
Hence then a clock consists of a wheel, or train of wheels, urged by a weight or spring, which strives continually to spin round, but its rotation is controlled by an escapement and pendulum, so contrived as only to allow it to go a step forward at regular equal intervals of time. ”

“ If the clock weight be enormously increased, the frictional retardation becomes increased relatively in a greater proportion than the drive, so that as the weight of the clock is increased the pendulum’s time of vibration is first diminished, until at last a neutral point is reached and finally the increased loading of the clock weight begins to make the time of vibration increase again. ”

“ If the weight is detached from the clock, the pendulum swings for a while before coming to a rest, but its motion becomes each moment feebler, and ultimately ceases entirely, being gradually used up by the small hindrances I have mentioned. Hence, to keep the clock going, there must be a moving force, which, though small, must be continually at work. ”

“ The clock most commonly used by the watch-makers as a "regulator" is one with what is called a "gridiron" pendulum. This consists of nine brass and steel rods, side by side, with their couplings so arranged that, in the changes of temperature, the variation of the brass counteracts that of the steel. Now, it is the fact that a large per cent of these pendulums are simply false "gridirons," while a very small per cent of the watch-makers are able to tell the difference. ”

“ In like manner if n=l/3 from either top or bottom, m must=M/7200 to accelerate the clock a second a day. The higher up the collar the less is the risk of disturbing the pendulum in putting on or taking off the regulating weights, but the bigger the weight required to produce the effect. ”

“ The seconds pendulum of the clock performs one vibration in two seconds, or a half vibration in one direction per second. Take a 10-inch pendulum of a drawing-room clock, which vibrates twice as fast as the pendulum of an ordinary eight-day clock, and it gives a vibration of one per second, a full period of one per second to and fro. Now think of three vibrations per second. I can move my hand three times per second easily, and by a violent effort I can move it to and fro five times per second. With four times as great force, if I could apply it, I could move it twice five times per second. ”

“ Now, if the pendulum could only be kept swinging and its vibrations [201] counted it would serve as a clock. Galileo, of course, saw this, and he caused to be made a machine for keeping the pendulum in motion (Fig. 11) , but he did not make a clock; he did not connect his pendulum with the works of a clock. This, however, was done about the middle of the seventeenth century, although it is somewhat difficult to tell who was the first to do it. The honor is claimed by an Englishman, a Frenchman, and a Dutchman. ”

“ Now, as in the latitude of London a pendulum which is a trifle more than thirty-nine inches in length swings once in a second, it is evident that, by lengthening or shortening the Pendulum, we have the rate of the clock entirely under command. ”