Popular Science Monthly/Volume 26/March 1885/The Accurate Measurement of Time

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944111Popular Science Monthly Volume 26 March 1885 — The Accurate Measurement of Time1885Theodore B. Willson



THERE are few people who have much knowledge of the present state of the science of measuring time. This is probably owing to the scarcity of sources of information on the subject, for almost every one has more or less interest in it. One might naturally suppose that his jeweler could discourse intelligently, if not profoundly, on such matters; but he is a very exceptional man if he has any considerable knowledge of the principles underlying the construction of the most common chronometers, so far as they employ principles not found in common clocks. In illustration of this ignorance of the subject, even among workmen who are thoroughly competent to treat all the disorders of time-pieces properly, and that to the degree of constructing broken or missing parts, or of mending fractures so nicely as to leave no trace of a break, the following instances may be given:

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. One might suppose that the running of the clock would reveal this at once. But it should be remembered that the variations of a clock on account of temperature are very slight. An abrupt change of ten degrees maintained through twenty-four hours wall cause a seconds pendulum to vary but a little over two seconds. Bearing in mind, then, that a pendulum may be timed to a mean temperature, and that thus the variations would tend to equalize each other; that, if the clock should thus come within a second a day, it would satisfy most watch-makers; and that as a matter of fact they ordinarily do change their "regulators" several times a year—we have little difficulty in accounting for the wide-spread ignorance of theory among them. To this may be added the consideration that there is no money in knowing about these things, and that to know about them takes time that might become money.

Again, we shall find our jeweler almost equally ignorant of the principles of compensation in the balances of watches. There are but few of them, indeed, who can not tell the genuine balance from the spurious, but there are hundreds of them who could not state, if life depended upon it, why the brass must needs be on the outside and the steel inside in such a balance, or why the converse arrangement would not be equally good, or whether the screws in the rim have anything to do with the compensation.

If, then, those who might be expected to know know so little, where shall we look for information? In view of the general ignorance of this matter and interest in it, a plain and untechnical account of the difficulties in the way of measuring time accurately with clocks or watches, and the progress that has been made in obviating them, may be profitable.

The whole matter of the accurate measurement of time turns, of necessity, on the manner of controlling the rate of escape of the mechanism which indicates the time. Thus far there are only two devices which have been found to do this with anything like accuracy, the pendulum and the balance-wheel. Postponing, for the present, the discussion of the balance-wheel, we have before us the pendulum.

That the pendulum might be used for the measurement of time is a discovery which dates back, at least, to the time of Galileo. A great many, even among well-educated people, suppose that that philosopher discovered that a pendulum of a given length will always oscillate in the same time. This he could not have discovered, for it is not true. The correct statement of the law he discovered is, that a pendulum will always oscillate in the same time through equal arcs, but not through any arc. It has been found that if the curve in which a pendulum swings were a portion of a cycloid instead of a circle, and the pendulum were simple, that is, consisting of a bob or ball suspended by means of a thread imagined to have no weight, its oscillations would be in equal times through any arc. To accomplish this, clocks were at one time made with pendulums which were suspended between cycloidal cheeks, and were thus conformed, in swinging, to the cycloidal curve. But this was soon abandoned, as it was found that it was impossible to construct such cheeks without variation or imperfection sufficient to make a greater error in the pendulum than it would have if allowed to swing on a circular arc. For a short distance the cycloidal curve corresponds quite closely to the circle. Therefore, by adjusting the pendulum to swing but a short distance, it was found to be possible to secure substantial uniformity. This is the plan now universally adopted.

If the arc of vibration is increased, the clock will lose time. Experience with the common house clock would seem to contradict this, for every one has noted that when the clock is first wound it will gain time, and then that it will lose as it runs down, and, seemingly, this is due to the difference in the swing of the pendulum. The explanation, however, is to be found in the fact that in case the pendulum swings farther it is shortened by the curving of the spring by which it is suspended, and also by an effect which the longer swing is found to have upon the escapement, quickening its time. Any ordinary house-clock would keep far better time if the weight of its bob were considerably increased, as this would do much toward equalizing its swing. Ordinarily the weight of the bob is about three ounces; if the clock is properly put in beat it will carry a bob weighing as many pounds, and all spring-clocks would be greatly improved as time-keepers by such a change. If this is true, some one may ask, Why is it not made by the manufacturers? The answer is, that any firm who should put such clocks on the market, superior time-keepers as they would really be, would soon find themselves getting the reputation of making a clock that would not run, and all because the public generally would not have the skill or the patience to adjust the beat properly. Let a servant, for example, take such a clock to her room at night, with the alarm set to call her up to get the family's breakfast. She sets the clock on an uneven table, and in a short time it will stop, and the girl will not be alarmed in the morning, except on discovering that the clock has stopped, and that she has far overslept herself. Thus, to make a sure clock, the manufacturers must make a poor one. For the best running of a fine clock it has been found that about twenty-seven pounds is the most satisfactory weight for the bob.

If it were not for what may be designated as meteorological changes, the problem of the accurate measurement of time would be solved if we had a heavy pendulum driven uniformly over a small arc. But here are two "ifs." We will take the second of them first, as it is more easily disposed of. Postulating at the outset machinery in the train very nicely executed, and with jeweled bearings so that it will act uniformly, or with the least possible variation, we have before us the question of propelling it uniformly. That the best power for a clock is a weight, is beyond dispute. The invention of the coil-spring came near annihilating the race of good common clocks. "Grandfather's clock," with its wooden wheels and other crudities, is still the superior of the grandson's clock as a time-keeper, for "grandfather's clock" had the great advantage of a uniform power sufficient and just sufficient to propel the clock when it was properly cleaned and oiled. The grandson's clock has a coiled-spring as a motive-power, having, when it is tightly wound, not less than three times the amount of power required to drive the clock, and diminishing in amount, thereby altering the rate of the clock, with each successive hour. The grandson's clock will march on, oiled or unoiled (and therefore usually unoiled), until it comes to a premature end as complete as that of the "one-hoss shay." The "grandfather's clock," on the other hand, which declined to go unless its rations of oil were doled out to it once in a year or less by the peripatetic tinker, is good for another century, since its bearings have been saved from cutting themselves away from lack of oil. The kitchen-clock of to-day can only be made to keep respectable time by so regulating it that the gain it makes when tightly wound shall be offset by the loss as it runs down. Something is gained in spring-clocks by resorting to the fusee—a device which maintains the power of the spring as it unwinds by giving it a greater leverage. This device was much employed by the makers during the early days of spring-clocks; but it was found to be so difficult a matter to secure a chain or cord for the connection that was reliable that the plan has been almost, if not altogether, abandoned. About the only opportunity of seeing a fusee to-day is in an English watch. It has been abandoned by watch-makers in America and in Europe, outside of England, so that the modern watch has no chain, and is made to go uniformly by adjusting to "isochronism," as it is called, which will be explained later.

Assuming that the power for an accurate clock must be a weight, we are ready to pass to the application of this power to the propelling of the pendulum, save this one consideration, that, unless there is some special provision, the clock will not advance while it is in process of winding. This provision is made in fine clocks by means of what is termed a retaining-click—an ingenious contrivance which brings the power of a small spring to bear while the key withdraws the power of the weight. This device is also found in the English—that is, the fusee-watch. Other watches need no such contrivance, for, as one end of the spring is fast upon the winding-post and the other upon the outside of the barrel, winding tends rather to stimulate and not to stop its going. The same is true of marine clocks. But common pendulum-clocks have the outer end of the spring attached to the frame of the clock, and hence the application of the key takes off the power, and the scape-wheel does not advance while the clock is in process of winding.

Supposing ourselves now possessed with a uniform power, uniformly applied to the scape-wheel, the problem arises as to the mode of communicating the power of the scape-wheel to the pendulum, in such a way as to sustain its beat, but not affect the time of it. Without going minutely into the discussion of the escapement, it may be remarked that there are two current forms of it. One of them is termed the "recoil" escapement, and its peculiarity is that it at no time arrests wholly the power of the scape-wheel—that is, it recoils by its own action after a tooth has passed one side of the verge, and returns toward the other beat. This is the escapement of the common kitchen-clock, and the chief objection to it is that, according to no definite law, the swing of the pendulum is made more rapid when the power of the spring is increased, as by winding.

A better escapement by far, and the one used in fine clocks, is the "dead" escapement, of which the characteristic is that, after it makes one beat, the pallet must be thrown off by the return of the pendulum before the scape-wheel can again apply its power. An example of this may be found in the ordinary marine clocks as well as in most watches, in which the lever is at rest after the balance has been thrown in one direction, until the return of the balance again trips it, and then its power is applied in the opposite direction.

This is found to be a satisfactory escapement for fine clocks which are not to be disturbed by any outside influences, but, for tower-clocks, which are affected by the wind, still another form is employed called the "gravity," or "remontoire" escapement, the principle of which is that the power of the clock merely lifts a small weight which is then unlocked by the swing of the pendulum and falls upon it, applying the uniform amount of its weight to propel the pendulum. There are, of course, two such small weights lifted alternately at each beat of the pendulum. The pendulum, therefore, has nothing to do with the scape-wheel except to unlock it. Absolute uniformity can be secured by this device, as the variations of the clock's power are not felt by the pendulum.

We come naturally now to the problem of maintaining an invariable length of the pendulum in spite of atmospheric changes. There is no substance known which does not expand in the case of a rise in temperature, and vice versa. It has been found, however, that white deal wood varies, with the grain, but very little, and hence it is employed in many of the better class of clocks, as being better than a cheap and imperfectly constructed compensating pendulum. Still, this does not give full satisfaction, as other changes, such as that from moist to dry, do affect it in a degree; and hence pendulums have been devised in which the variation of one metal is counteracted by the variation of another in the opposite direction.

The most common form in which we see such pendulums is the so called "gridiron," which takes advantage of the greater sensitiveness of brass than of steel to changes in temperature. It is made with nine bars of brass and steel alternately arranged, the total length of brass employed being to the steel inversely as the two metals are affected by changes of temperature. It is constructed so that the brass lifts the bob in case of a rise in temperature as much as the steel lets it down. To illustrate the principle of it, imagine a simple pendulum rod of steel; to the bottom of this fix a rod of brass slightly shorter than the steel one, letting it extend upward parallel with it; let a second steel rod now be affixed to the upper end of this brass one, also parallel to the others, and to the lower end of this attach the bob. We have now a gridiron pendulum, but one in which the amount of brass is not sufficient to counteract the changes in the steel. Before it will do this, we must make one more journey up with a brass rod and down with a steel one, affixing on this the bob. To construct such a pendulum it is found necessary to duplicate the first four rods; hence the nine that we always see. The genuine "gridiron" is a pretty good clock, but it is so often spurious that this kind of clock is going out of favor.

A third common device is the mercury pendulum, consisting of one or more cylinders filled with mercury to such depth that the movement of the highly sensitive mercury in the bob will counteract that of the entire rod. This is readily understood by viewing the center of the mercury as the center of oscillation (which it is very nearly), and imagining that the temperature rises. Of course, this center is carried upward half as much as the surface, and so great is the variation in the case of mercury that a vessel of it about six inches deep will counteract the steel rod of a seconds pendulum. This is the pendulum employed for fine astronomical clocks, and all jewelers who can afford them have them for regulators. The only objection to this pendulum is that the mercury, owing to its mass, is not affected by a change of temperature quite so promptly as the slim rod of the pendulum. But this is not found to be a serious matter.

Of late, zinc has been coming into use in the construction of compensating pendulums. The best tower-clocks now all have zinc pendulums. The principle and the application are the same as in the "gridiron," but the higher sensitiveness of the zinc simplifies the construction to such an extent that, only one return-rod of zinc being called for instead of two, as in the case of the brass, it can be made in the form of concentric tubes, and thus appear as a simple rod.

Such are the principal devices for securing compensation. There are many other ways of reaching the same end, and patents have been issued for ingenious designs, no one of which, however, has come into general use.

But, even with a pendulum compensated with brass, zinc, or mercury, we have not yet conquered the problem of measuring time with great accuracy, for, aside from the practical difficulties of obtaining homogeneous material and getting the proportions of the metals exact, there is yet to be taken into account another cause of variation which one could only be convinced by demonstration is capable of having any appreciable effect. It is that of atmospheric pressure. It has long been known that clocks vary somewhat with the barometer; and, of course, we see that they must, when we remember that a heavier or denser atmosphere tends to decrease the gravity of all objects—to bear them up, as it were—and hence, when the barometric pressure is greater, a clock will run slower. To counteract this, a magnet is resorted to, which is made to approach or withdraw from the pendulum by means of the rise and fall of the barometer. This is placed, of course, below the pendulum, and if nicely adjusted will keep the weight of the pendulum uniform.

If all the above disturbing elements are met by counteracting expedients, we now have a clock which will theoretically run without variation, provided it is once brought into the proper beat. A thumbscrew at the bottom of the bob will accomplish this approximately, but, to do it with the greatest accuracy, it is necessary to have a little cup suspended on the pendulum-rod near its upper end, into which one can drop some small weights, as shot, quickening the variation thereby, since it is a virtual raising of the center of oscillation. Fine astronomical clocks usually have this cup, and the best turret-clocks also.

It is at this point interesting to inquire how closely a clock, constructed in observance of all these principles, can be made to run. Generally speaking, it may be replied that it is a pretty good regulator which can be depended upon for a variation of less than a second a day, through all weathers, despite what is claimed for them by their owners. A distinction must be made between a uniform variation and keeping a mean time. I have a common eight-day spring-clock which does not seem to vary a half-minute in a month. This is, perhaps, better than many regulators do; hut, while it does not make an average variation of a second a day, it is far enough from making an actual variation of less than a second a day. Something better is obtainable from the very best astronomical clocks, which, indeed, are found to keep a uniform rate, from which they will vary only three or four hundredths of a second daily. But astronomical clocks, as is well known, are not required to indicate the exact time, mean or sidereal, but only to go at a uniform rate, which, if it be found to be practically invariable, is corrected at the time of the observation in which it is employed. The most accurately running large clock in the world, which has been regulated to keep diurnal time, is the Westminster clock in England. When the contract for the building of that clock was given out, it was stipulated that it must come within a second a day. It, in fact, does much better than this, for it is found that its variation is usually less than a second a week. It telegraphs its time daily and automatically to Greenwich, and the astronomer royal has said of it, "The rate of the clock is certain to much less than a second a week."

The other practical method of regulating the escape of a timepiece is through the balance-wheel, which, of course, must be resorted to in case of watches, ship-chronometers, and all clocks which are to be moved or carried about.

The method of regulation now in use in the watch is the result of long study of ingenious men. Starting with the discovery of the balance-wheel, carried back and forth with a diminishing oscillation by means of the hair-spring, we have before us the question of how to unlock the scape-wheel with each swing of the balance. In hunting through all classes of watches which find their way into the jeweler's refuse-box, after having served out their period of usefulness, we shall not be likely to come upon more than three (and certainly not more than four) styles of escapement. The oldest watches in the box will have what is termed the horizontal or barrel escapement. This is the escapement of the so-called "bull's eye" watch of our grandfathers. These watches always had a great reputation as time-keepers, yet I presume it is safe to say that there never was one in existence which could be relied upon to keep within a minute a day in the pocket, and most of them needed a much larger allowance. This escapement had a small wheel, with its axle parallel with the plates of the movement, and its teeth acted upon the pallets, which were little, flag-like appendages to the staff of the balance, and set at right angles to each other. The chief defect of it was, that a slight variation in the power, acting directly as it did upon the balance, affected very materially the rate of the watch. So that, while our grandfather's clock was even a better time-keeper than clocks of the same grade manufactured to-day, our grandfather's watch is not to be named in comparison with the cheapest modern watches.

The second class of escapements which we shall find exampled in the waste-box is called the cylinder escapement, which still continues to be used in some of the cheaper Swiss movements in boys' watches, and such as the ladies wear suspended from the belt. It is the most compact escapement which has ever been made, and is employed in such very small specimens of the watch kind as are made to be set in the head of a pencil, a shirt-stud, etc. It is by far the most reliable escapement except the lever. Its principle is that the cylinder of the balance-wheel is so cut that each tooth of the scape-wheel must force it partly round to get past it. While it is making this turn, the next tooth of the scape-wheel is caught upon the blank side of the cylinder, and held until the recoil of the hair-spring brings the balance back.

Here and there a specimen is to be found of the old "duplex" escapement to which the modern "Waterbury" is allied. It is so rare as hardly to need our consideration. It is a good escapement when in order, but is rather liable to get out of order.

A third form of escapement, and the one now in use almost universally, is the detached lever. There are patent levers, straight-line levers, and various other levers, but they are all detached levers, for the reason that there is one point, in the course of each swing of the balance, when the lever is entirely free or detached from the balance-wheel, and so stands until the return-swing unlocks it. It is difficult to conceive of anything that would be an improvement upon this, and seemingly no improvement is needed.

Before we pass from the consideration of the escapement to that of the balance itself, a remark should be made as to the relative advantages of different rates of escapement. It is found that up to a certain point what is called the quickness of the train, or, in plain English, the rapidity with which a watch beats, makes a difference with its qualities as a time-keeper. This seems to be owing to the fact that where a watch beats more slowly it is more apt to lose an occasional beat through the jar and tossing about in the pocket. The Swiss manufacturers took the lead, and have for forty years or more made quick-train watches, beating five times to the second, or eighteen thousand times to the hour. The English watches commonly beat four times to the second, or fourteen thousand four hundred to the hour. American watches are made with the quick train of the Swiss, but more commonly with a beat intermediate between the two extremes. It is curious that the English, who have given so much money and thought in the past to the manufacture of time-pieces, do not to-day make a good watch nor a good common clock. Their adherence to the slow train is one of the reasons of their failure in watches, and their retention of the fusee is another. So great has been the decline in the English trade in watches and clocks, that a number of their experts in that line recently recommended petitioning the Government to cause an official investigation to be made to learn its causes, and what can be done to arrest it and restore the trade.

Perhaps we ought yet to pause, before taking up the balance itself, to take note of a form of escapement employed in chronometers (using the word in its strict sense as applied to clocks which may be moved, but must not be jarred or tossed about, and are to remain in nearly the same position). In this escapement the tooth of the scape-wheel acts directly upon the balance, and after so acting is caught upon a shoulder, from which it is only released by the return of the balance. Better results have been obtained with this than with the detached lever for chronometers, but it is not so good for watches, as it will not bear violent and sudden tossing about into all positions.

To measure time accurately with a balance-wheel, three sources of variation must be overcome—that is, the balance must be adjusted to heat and cold, to position, and to "isochronism," as it is termed—that is, it must in some way counteract its own variation, due to temperature as well as that of the hair-spring; its bearings must be so cut or shaped that changes of position will not occasion unequal friction; it must be made to beat uniformly, in spite of the variations in power which result from doing away with the fusee.

The method of compensating a balance is to-day everywhere the same. A compensated balance consists of a bar of steel, to the opposite ends of which are attached semicircular bows of brass and steel soldered together, the brass outside, and into these bows are screwed what are termed "set-screws." It will be seen that, in case of a change for the warmer, the brass outer rim will expand more than the inner steel one, in each of the arms, and that this will throw the extremities of the arms in toward the center, thus compensating, if the proportions are right, for the general expansion of the balance; and vice versa in case of a change for the colder. Of course, it is a very nice piece of experimentation which ascertains these proportions. After the approximate proportions are secured, the exact ones are obtained by means of the screws in the rim. Compensation in a balance-wheel is of far more importance than in a pendulum, for the variation of the rate of the time-piece, if not compensated, is far greater. And this is due not only to the expansion and contraction of the balance, but also to the variation in the power of the hair-spring under various temperatures, as above remarked.

I may pause to note that here is one of the tests of a watch that any one may resort to. There are many imitation compensating balances which look very like the genuine, save that they have not the cut, or have only a notch at the extremity of the bow, so that the bow is not free, and, of course, there is no compensation.

After a watch has been adjusted to heat and cold, it must be adjusted to "position"—that is, so that its rate will not be altered by changes of position. This is a nice piece of work. It is accomplished by shaping the pivots, blunting them or sharpening, according as it is found to be necessary.

The third difficulty named was that of preventing the different pressures of the mainspring (as when it is tightly wound or nearly run down) from altering the rate of the watch. This is effected in the following manner: It is found to be a fact that there is a point in any hair-spring at which, if it be secured, it will carry the balance-wheel at the same rate no matter what the force of the train. This point can only be discovered by experiment, and the discovery of it constitutes the adjustment of the watch to what is called "isochronism." By continually shifting the point where the hair-spring is pinned, a point is finally discovered where the watch goes at a uniform rate, which may be too fast or too slow, but it is uniform. This point ascertained, the watch is then made to keep diurnal time by shifting the screws in the circumference of the balance.

Of course, it greatly increases the expense of a watch to add these fine touches by the best skilled workmen; and yet so perfect is the machinery to-day and so closely does the watch when first put together conform to the well-understood proportions that in point of fact a large per cent of them are found to be correct, and need little or no adjusting. In this case they are simply marked "Adjusted," and sent to market. The leading American factories have discontinued the manufacture of watches which have not compensating balances, so that, even though the watch be of cheaper grade, it will still run far better through all weathers than the best watches with a solid balance.

In the American watch we may well take a patriotic pride, for it is the best watch in the world; and, what is more, it is being imitated everywhere. Its only real rival is the Swiss watch, the better grades of which can hardly be said to be inferior as time-keepers to American watches. The cheaper grades, however, will not rank with the same grades of our watches.

After a watch has been given all the advantages of adjustment described, it is interesting to inquire how closely it will run. But, lest we expect too much, it is important that we keep in mind that a watch is at great disadvantage in comparison with any other time-keeper, for it can depend upon no uniformity either of rest or of motion. No two men's habits of life are such as to give their watches exactly the same jar and disturbance. One man's watch is laid down at night, and another's is hung up; one man's is in the cold, and another's is where it is warm; one man is much upon the rail, and another seldom travels at all; one man's habits of life take him into those sorts of dust which soon clog the oil of his watch, another is never in any dust. Add to all these considerations one more, namely, that a watch will run a little freer, and hence a little faster, when the oil is fresh, and of course will slow down as the oil gets old, and we have abundant reason for great leniency in judging of the work of these really marvelous machines.

Remembering these things, we shall be prepared to accept the stories about the wonderful running of some watches with more or less allowance. That watches sometimes seem to go with very slight variation for long periods of time is often accounted for by the fact that the accelerating and the retarding effects in the carrying of them have nearly counterbalanced each other. A good watch may be so nicely regulated as to keep a mean time between its variations, which will be very accurate. I have heard of two watches in the course of my life for which their owners claimed that they varied only four seconds a month, and I can not help adding that they sought to touch the regulator just once more to overcome even this variation. With one of these men I had a personal interview, and succeeded in drawing out that, after all, he was not telling what his watch varied, but only how it stood at the end of a month; for aught he knew, it might have ranged a minute or two either way during the time. The other man I never met; but I trust these are the only men in the world who ever imagined that a pocket time-piece can be made to have a uniform variation of less than a second a week. But such men serve as an example of the misfortune it really is if one possesses too good a watch. When a man gets to reading the time on his watch by the secondhand, he is likely to feel discouraged and out of joint with the world much of the time, for his watch will not bear such scrutiny. A far happier man is he who can only afford a poor old "turnip" which, like Sam Weller's, must be set twice a day. A man who possesses one of these wonderful watches, supposed to run to the second, could hardly feel worse to find himself coming down with the cholera than to find that without seeming provocation his watch has gained or lost twenty-five seconds,

I add a few remarks upon the use and care of time-pieces, their visits to the jeweler, etc.

It is to be observed that there are many unscrupulous men working at the bench who have very little real knowledge of their trade, and who, to make a living, must make the most of what they get to do. Such men uniformly declare that any watch which comes into their hands to be repaired needs cleaning, which will cost you from a dollar to a dollar and a half. Sometimes this is true, and sometimes it is not. If you have a stem-winder in a close-fitting case, it is probably not dirty, and yet, if it has run two years or so, it ought to be oiled. This most jewelers will do, if you ask them to, for a small fee. If I owned a fine watch, my practice would be to take it to a jeweler, and have it thus oiled once a year, having it cleaned perhaps once in three.

If a jeweler tells you that there is some very serious trouble or break in your watch, which it is going to cost several dollars to get repaired, ask him to take the watch "down," as he terms it, and let you see that trouble. An honest man, not overdriven, is always ready to do this.

It is a little better to wind one's watch in the morning than at any other time, since, if you wind at night, and then expose your watch to the cold, the chilling of the mainspring is more apt to break it when tightly wound.

Empty out the dust that accumulates so quickly in your pocket often; it will save your watch from the unnecessary contact and battle with dirt.

It is amusing to hear an ignorant customer betray a fear lest a jeweler shall steal some jewels from his watch while it is in his possession. A friend of mine, who is a jeweler, in such cases always reaches for his bottle in which he keeps his watch-jewels, and asks the customer to hold his hat while he turns them in. This usually brings the customer to his senses. In point of fact, a large part of the jewels in common watches are nothing but glass. Next comes aquamarine or beryl, then garnet, then ruby, and rarely sapphire. But even a ruby-jeweled watch is a very rare commodity; and even these rarer stones would be of very little value for any other purpose, perforated as they are for the pivot; and the fear lest the jeweler may steal them is simply ludicrous.

There is an amusing superstition, which has not as yet wholly disappeared, that a watch ought not to be turned backward. I hardly need remark that this is wholly groundless, for the "cannon-pinion," as it is called, that carries the minute-hand, is wholly independent of the train, and merely rests upon the prolonged pivot of one of the train-wheels, on which it turns with slight friction; and, indeed, if it should fit too closely, it would be more likely to damage the watch if it were turned forward than backward. The same thing holds in case of a clock, of course, save that, in case of a striking-clock, a backward turn after the "snail" has unlocked the striking-gear, and the clock is about to strike, will cause it to do so, and hence it will strike wrong. And, of course, after it has struck in the ordinary way, it can not be turned back far without the snail's catching on the outside of the lifting-wire. This will make it impossible to turn it back farther. But no turn will in any way injure the clock.