Helpful Information for Watchmakers (3rd Edition, 1918)

HELPFUL INFORMATION WATCHMAKERS BY 0LOF0HLS0N GENERAL SUPERINTENDENT 3d Edition 30,000‐1918 WALTHAMWATCHCOMPANY WALTHAM, MASS. FOREWORD WE take pleasure in providing for Watchmakers this booklet containing a brief explanation of certain recent improvements that have been made in the mechanical construction of Waltham Watch Movements. We have also added a few notes of a more general character, which we trust will be of interest and some usefulness. WALTHAM TAPER SHOULDER DETACHABLE BALANCE STAFF (PATENTED) As used in OS, 1900, 12s, Model B Colonial Series and 16s, ‘99, Waltham Movements This is an improved form of a detachable Balance Staff that is certain to appeal to the watchmaker, as it admits of easily and quickly changing a staff without bending the balance arm or throwing the balance out of shape. The bevel seating in the hub B fits precisely the taper shoulder F on the staff, thus insuring a level balance. To drive o u t an oldstafi,werecommendusingatoolasshowninFig.4; toputinanewstaff,apunch,as showninFig.3,bringingthetaperedshoulderonthestafftoitsbearinginthehub. Tools designed for these staffs can be obtained from watch t o o ] manufacturers in sizes to fit regular staking tool sets. The blue steel hub should always be left in the balance arm when changing a staff. | ‘a,ll“| 4:55:51;0.s OHM/VG//y 7bOL. flfi/V/A'e Our 7bOL. 4 DH L m , MUM? 72/pr fflouwffi [JAE/27mm5414/fo J 71W. ‘\ x iW WALTHAM HAIRSPRING STUD A common practice in removing a watch balance, is to lift it by the hair‐ spring, whose stud is left attached to the balance cock. This method, while con‐ venient, involves the danger of possible injury to the hairspring. By the improved stud, herewith illustrated, such danger isavoided. It is simply needful to t u r n back the stud-holding screw sufiicient to allow the stud to swing freely from its place, thus detaching the hairspring from the balance cock which can then be removed. After replacing the balance, screw the balance cock into place, then hold the move‐ ment onedgeandallowthestudtoswingintoposition,thenfastenintoplacebyitsscrew. WALTHAM SPIRAL WINDING,PINIONAND CROWN WHEEL As used in the latest 12and 16size movements The Waltham Watch Company has solved the difficult problem of transmitting power, at a right angle, from the winding arbor to the winding wheel. smooth winding action is produced by the special form of spiral teeth of the Winding Pinion and the rounded cycloi‐ dal working faces of the teeth in the Crown Wheel, as shown in the accom‐ panying drawing. For the making of these parts, special automatic machin‐ ery has been designed and built at the Waltham factory. An absolutely WALTHAM SAPPHIRE JEWELED MAIN WHEEL Asusedin our18sVanguardandCrescentStr.’92modelmovementswith19ormoreJewels; 16s’99modelmovementswith19or more Jewels; 14sColonialA; ColonialSeries and 12s Riverside and Maximus grade movements. This main wheel is fitted with two jewels, forming the bearings, which t u r n on the barrel arbor during the running of the watch. As shown on page 8, the arbor is composed of two parts, A and B. Part A is squared on its upper end to receive the winding wheel; next to this is a round part (with a shoulder) that turns in the plate during winding. Below this shoulder or flange is the body of the arbor, on which the main wheel turns. It has an axial hole through its entire length, tapped with a double right-hand thread. Into its lower end is screwed part B, which, with its square and shoulder, holds the steel barrel in place. To separate, hold the barrel by the thumb and finger of one hand, place on the square of the winding arbor the winding wheel or a key, and t u r n backwards. A special tool for this purpose, asshown in the illustration on page 8,can beobtainedfrom dealers in watch tools. www 1W1 IIIIW \ HMIIIIIIIIHIIIIIH ‘4 ll/l/l/ // W a i n Me (26 and‘é‘a/weé Msaemblect. J’Zfl/NMAEEL, ”474W'‐C9. 11fw1mmu..\.1.\1\.1\111111111111\| \/ “511111 ’J/// //////////// WALTHAM RECOILING CLICK Theobjectinusingarecoilingclickistwofold: first,toreleasetheinitialhightension after the winding of the watch, resulting from torsion in the barrel arbor and abnormal stress in the main‐ spring which some‐ times, when a plain click is used and the w a t c h is wound care‐ lessly, will cause the balance to “over-bank” and gain time in a very erratic way. Second: If a mainspring is wound very tight, and not released immediately, the oil will be squeezed out, causing excessive friction between the successive turns of the spring, resulting in a falling off in the motion of the balance. These difficulties are overcome in a very efficient manner by the use of o u r recoiling spring click shown in t h e illustrations here‐ with. 1‘ WALTHAM TAPER STEADY PINS In theplateworkofwatchmovements,steadypinsareusedforthepurposeofplacing, and accurately relocating, parts that have to be removed at times for cleaning, etc. Steady pins should fit closely in their holes, and still let go freely when the screws are loosened. Under such conditions there is very little danger of bending or breaking pivots, in p u t ‐ ting together, or taking apart, watch movements. Theserequirementsarebroughtto perfection in Waltham Watches by the taper steady pins and holes. (See drawing.) These are made on special automatic machines, by which the watch plate and the part that is to be fitted are held firmly while the pins are turned and the holes in which they are to fit are bored at the same time. This method ensures exact location as well as proper fit. 12 WALTHAM PENDANT SETTING MECHANISM The Waltham Pendant Setting Mechanism consists of the Shipper A, Shipper Lever B and Shipper Spring C. The normal position of these parts with the setting teeth of the clutch in engagement with the hand setting wheels, is shown in the accompanying drawing. If the watch is to be ' r u n out of the case, the shipper bar D should be pulled outward. This acting on the shipper at E shifts the clutch from the setting to the winding position and leaves the setting wheels free. THE SIZE OF A WATCH MOVEMENT As a matter of interesting information relating to thedescriptionof Americanwatch movements, as being of certain designated “sizes,” let us say that this system of meas‐ urement is identical with that established and used by English watchmakers, and relates to the extreme diameter of the pillar plate. Being English, its unit of measurement is the E n g l i s h i n c h , a n d t h e z e r o , or s t a r t i n g p o i n t , is one inch plus five-thirtieths of an inch (1350), w h i c h is the diameter of an 0 size movement. Each go- of an inch added to this measurement represents the size of a movement. Therefore 1350 plus 310 will be the diameter of a one size movement; a six size should measure 1‐5‐5, a twelve size lgg, an eighteen Size lgg, etc. N O T E : In order to express this in millimeters we must multiply by 25.4, which is the metric equivalent of an inch, sothe general formula will be (gal-5513?) X 25.4; and the formula for 12size, (gig‐PH) X 25.4 = 39.8 millimeters. 13 WALTHAM LEVER ESCAPEMENT The proper action of the human heart is no more essential to insure a sound and healthy body, than is the properadjustment and action of the escapement to the reliable performance of the watch. If the watch escapement is properly made and adjusted, it will n o t only r u n , ‐but will r u n with marvelous accuracy. So the time-keeping qualities of the watch are in large measure dependent on the condition of the escapement. It is, therefore, of great importance that every watchmaker should acquire an intimateknowledge of all the actions that are involved in the kinds of escapements with which he has anything to do. The only kind of escapement used in Waltham Watches is the detached lever escape‐ ment, sometimes designated as the anchor escapement. This escapement requires no special introduction to watchmakers, for by extensive use, and by the test of time, it has beenproven to be the most practical as well as the most reliable form of escapement for pocket timepieces. We insert in this booklet some drawings of the lever escapement that they m a y be convenient for reference, and an aid to the clear understanding of the test. The function of the escapement is to impart to the balance, regularly, and with as small loss as possible, the power which has been transmitted through the train from the mainspring to the escape pinion. In the lever escapement this is accomplished by means of t w o distinct actions:‐ first, the action of the escape wheel and pallet; second, the action of the fork and roller pin. The drawing on page 16 is a plan view of the Waltham Lever Escapement, as used in the 16size, 1899, and 18size, 1892 model, movements, drawn toscale10tol, andgivingthenamesoftheprincipalpartsandfeaturesofthesame. The Loam/c5405 \ WPULSEfiref ‐ ‐ » 604/90 P/IV \\\‘f// \ ‐‐‐‐‐ ’,‐_§\ \\ . I,/ \ \ HOLLfR // \\ escape wheel is mounted friction tight on the slightly tapered staff of the escape pinion. It hasfifteenteeth,called“ClubTeeth”onaccountoftheir peculiar shape,resultingfrom t h e a d d i t i o n o f i m p u l s e faces t o t h e ends o f t h e t e e t h , a n d t o d i s t i n g u i s h t h e m f r o m “ r a t c h e t teeth,” the n a m e givento a style of pointed teeth used on escape wheels in an earlier f o r m of lever escapement. In descriptions of this escapement the t e r m “exposed pallets” is used. This means that the pallet stones are visible, with the active ends standing out free from the body of the pallet, asdistinguished from an earlier form of pallet with “covered stones” set in slots running in the plane of the pallet. THE PALLET ACTION The action of the escape wheel and pallet includes the following features: impulse, drop, lock, draft and slide, and in giving a general description of these actions we will con‐ sider briefly what constitutes each one of these features. The pallet is of the kind called “circular pallet,” which meansthat the distance from the pallet arbor to the middle of the impulse face is the same for both pallet stones. Another kind of pallet is made with “equidistant lock,” that is, the distance from the pallet arbor to the point where the lock takes place, is the same for both pallet stones. The pallet is mounted on its arbor, which is located close to the periphery of the escape wheel. A theoretically correct distance in , relation to the diameter of the escape wheel will n o t allow an excess of clearance between the pallet and the escape wheel teeth when opposite the pallet arbor, and for that reason the amount of stock in the pallet is made very small at that point. The pallet is slotted 1WALTHAM 1 for the two pallet stones in such a way as to make the inside corners of the pallet stones reach over three teeth of the escape wheel, and to make the outside corners of the stones reach over two teeth and three spaces of the wheel, with a small a m o u n t of clearance in each instance, which is called the “drop.” One other important p o i n t in relation to the slotting is to direct the slots in the p a l l e t i n s u c h a w a y a s t o m a k e t h e l o c k i n g faces o f e a c h o f t h e p a l l e t s t o n e s p r e s e n t t o t h e locking corners of the escape wheel teeth a certain angle.of “draw” when the stones are in the position of “lock.” We will t r y to make this condition clear by referring to the drawing on page 22. Suppose that the escape wheelis being forced in the direction indi‐ cated by the arrow, but is prevented from turning in that direction because the locking face of the R pallet stone is directly in the way of a tooth. The particular tooth which is resting on the pallet stone is exerting a certain pressuredirectly towards the pallet arbor. If thelockingfaceofthepalletstonewerealongthelineB,whichisatarightangletothat lineofpressure,therewouldbenotendencyforthepallettoturnin eitherdirection,but being along the line C, which forms an inclined plane in relation to the direction of the pressure, the pressure applied by the escape wheel tooth will tend to pull the pallet stone toward the escape wheel. This action is called the “draft” or “draw.” The turning of the pallet is, however, limited by the banking pin, and the object of the draw is to keep thefork againstthebankingpinallthe timethatit isnotin engagementwiththe jewel pin. This action of “draw” is similar on the L stone; the only differences are, first, that the pressure of the escape wheel tooth is exerted in the direction away from the pallet arbor, instead of towards it, and, second, that the turning of the pallet, which in this instance is in the opposite direction, is limited by the other banking pin. ‐ A glanceat the drawingon page22willmakeit apparentthattheimpulseface,which is formed by the surfacebetweenthe locking and the let-off corners, is at a different angle on the R from that on the L stone. The impulse angles of the stones in the escapement, represented by this drawing, are, on the R stone, 6°30’, and on the L stone 18°. The above refers in each instance to the angle of the impulse face in relation to a r i g h t angle to the locking face, or to the body of the stone. From this condition and from the direction of the pallet stones in relation to the body of the pallet, the factory names “straight” and “crooked” have been given to the R and L stones, respectively. In books and treatises on the lever escapement the names “receiving” and “discharging” are used, but when, as a matter of fact, both pallet stones perform the functions of receiving and discharging, one asmuchastheother, thesenamesdonotseemto beappropriate. Forourpartweprefer to use the letters R and L to distinguish one stone from the other, and these letters m a y easily be remembered as right and left, this being the order in which the stones appear as we look at the top of the pallet with the fork turned towards us. The impulse or l i f t is divided between the escape wheel clubs and the pallet stones; the two together cause the pallet to turn through an angle of 8°30’; the lock amounts to Loaf/Ne5405 \ ‘WPULSE54sz " 7 ° " 604,70 P/A/ \\\ \ \ ROLLffi \\, \\\ \__,/ ,/ from 1° to 1°30’, making the total angular motion of the pallet about 10°. This is the condition when the pallet is “banked to drop,” that is, when the teeth of the escape wheel willjustbarely passby thelet-oficornersof thepalletstonesastheforkcomesto restagainst the bankings. A certain a m o u n t of clearance, or freedom, has to be added to this to allow f o r o i l , e t c . , s o t h a t t h e b a n k i n g s have t o b e t u r n e d a w a y f r o m t h e c e n t e r l i n e a s m a l l a m o u n t t o a l l o w f o r w h a t i s c a l l e d “ s l i d e , ” t h a t i s , t h e p a l l e t s t o n e w i l l slide a v i s i b l e a m o u n t i n t o the escape wheel, after the escape wheel tooth drops on to the same. The amount of slide should, however, be very small, because it causes loss of power, by increasing the resistance to unlocking, as, in order to unlock, the escape wheel actually has to be turned backwards against the power of the mainspring, and the a m o u n t of this recoil is in proportion to the lock and slide added together. It is therefore important to notice the action of every tooth of the escape wheel on both pallet stones, to ascertain that each pallet stone has some slideoneverytooth,andtoallowonlyasmallamountintheplacewhereit appearstobe closest. 23 ROLLER AND JEWEL PIN One problem in connection with lever escapements, which every watchmaker has hadmoreor lessexperiencewith,hascometo afinalsolutionin theWalthamDoubleRoller Escapement. This is the fastening of the jewel pin. The roller, which holds the jewel pin,ismadeofbronze,withaholein it theshapeofthepin,butacertainamountsmaller than the pin. The jewel pin is made of sapphire, and is made slightly tapering, and is forced intothe hole in the roller, thus making it permanently secure. The shape of the jewel pin is round, with one side flattened off to measure three-fifths of the diameter of the pin, and the sharp corners removed. This form of jewel pin is superior in general practice to any other form, asit unites strength with the most desirable shape at the points of action. The principle of setting the jewel p i n directly in the roller, without cement, is made possible by the Double Roller Escapement, because of the special roller for the safety action. It would n o t be practical to set jewel pins without cement in steel rollers as it is in bronze, neither would it be advisable to use bronze roller for the safety action, because it has been found by experience that tempered steel is better for that purpose. But, by separatingt h e t w o features, it makes a m o s t desirable combination to use a bronze roller for carrying the jewel pin, and a separate steel roller for the safety action. 26 MATCHING THE ESCAPEMENT The term “matching the escapement” is used to designate the work of bringing the different parts of the escapement into correct relation to each other; in other words, to make the necessary moves in order to obtain the proper lock, draft, drop, slide, fork length, let-off, etc. The best way of learning to do this work is to have a competent in‐ structorwhoisathandreadytoinspectandtogiveadvice. Thedifficultiesarenotsogreat in doing this work, as in correctly determining what to do, in order to bring about certain results, and also to know when the escapement is in a proper condition. It is difficult to give in writing a comprehensive idea of how to do this work. We will, however, give a few points which we hope will be useful to the beginner. T h e fi r s t t h i n g t o receive a t t e n t i o n i s t h e c o n d i t i o n o f t h e p i v o t s o n t h e escape p i n i o n , palletarborandbalancestaff,to seethattheyarestraight,andthattheyfit properlyin their respective holes. It is absolutely necessary that each pivot should have some side shake, b u t it is also very important to guard against too much side shake, as such an excess causes loss of power and uncertainty in the action of the escapement. A desirable amount of side shakeis.01mm.,andit shouldnotexceed.015mm.,andtheamountofendshakeshould be from .02 to .05 m m . As soon as these points have been found to be correct, we are ready to t r y the “lock” and the “drop.” In describing the pallet action, on page 23, we made the statement that the lock should amount to from 10to 1°30’ This statement is, of course, of no practical use unless we are equipped with the necessary instruments for measuring this angle. We m a y , however, use the thickness of the pallet stones for com‐ parison and obtain practically the same results, by making the amount of lock equal to 1107 to %thethicknessof thestone,fromthelockingto the let-off corner. This corresponds very closely to the above angular measurements. If the pallet stones are to be moved, in order to change the a m o u n t of lock, it is very important to first consider what will be the 28 effect of a certain move, besides the alteration of the lock. The drop, for example, is effected very rapidly by moving the L stone. Hence, if the drops are equal, we should make the change in the lock by moving the R stone. If the lock is too strong, and the drop is largest on the outside, the L stone should be moved. If the lock is too strong, and the drop is largest on the inside, it is necessary to move both stones. Move the L stone o u t a small amount,andmovetheRstoneinuntilthelockiscorrect. Itisalsowelltorecognizethat the drop m a y be modified to a certain extent by moving the pallet stones, close to one or the other side, in the slots, as there is always some room allowed for the shellac which is used for holding the stones. The moving of the pallet stones in or out in the slots will also affect the draft feature of the escapement; this is a point which we should bear in mind whenever we make a change in the position of the pallet stones. The effect from moving the R stone o u t is to increase the draft on both stones, whereas if the L stone is moved out and the R stone in, it will decrease the draft. In order to ascertain that the escape wheel is correct, the lock and the drop should be tried with every tooth in the wheel onbothpalletstones. Thisshouldbedonewiththebankingsadjustedclose,soastojust permit the teeth to drop. And the best way to t r y this, is to move the balance slowly with the finger while the pallet action is observed through the peep holes. After completing the adjustment of the pallet action, the jewel p i n action is n e x t to be considered. The fork should swing an equal distance to each side of the center line when the pallet is banked to drop. If we find that it moves farther on one side than on the other, it will be necessary to bend the fork close to the pallet a sufficient amount to bring it in line. This is called, “ t o adjust the let-off.” The test for the let-off is to see that when the pallet is banked to drop, the jewel p i n is just as close to the corner of the fork, in passing out, on one side as on the other. This test is correct, provided that the fork is of equal length on both sides of the slot, as it should be. The test for the fork length is that is should allow the jewel p i n to pass o u t on both sides when the pallet is banked to drop. This is the maximum 29 length which is allowed for the fork. The test for short fork is to move the balance so as to unlock the pallet, then reverse the motion and see that the pallet is carried back safely to lockby thejewelpin. Thisshouldbetriedon both pallet stones. It is,however,cus‐ tomaryto trytheshakeof the fork when the center of the jewel pin is opposite the corner of thefork,andnotto allowthepalletto unlockfromthisshake. In orderto ensure perfect freedomin thejewelpinaction,thejewelpinshouldbefrom.01to .015 mm. smaller than the slot in the fork. The safety action is also adjusted, while the escapement is banked to drop. The guard p i n should be made just barely free from the roller when the fork is against the banking, and this should be tried carefully on both sides. If this is done cor‐ rectly, the roller will have the necessary clearance when the bankings are opened to allow for the slide. The operation of moving apallet stone is one that requires agreat deal of experience before one is able to do it satisfactorily except by repeated trials. Special tools called “pallet warmers” have been devised for holding the pallet during this operation. In the simplest form this tool consists of a small metalplate, about aslarge asa 12size barrel, with a wire handle by which it is held while it is heated. This plate should have one or m o r e holes drilledin it as clearance fOr the pallet arbor. An improved f o r m of this tool is shown on the following page. This tool is provided with a spring clamp for holding the pallet to the plate. The pallet is placed top side down against this plate, and the whole of it is warmed over the alcohol flame until the shellac is softened so the stones can be moved. A good way of applying shellac for the fastening of pallet stones is to w a r m some stickorbuttonshellac,overaflame,andpullit outin longthreadsofabout.5mm. diameter. Shellac in this form is very convenient to use, as it is only necessary, when the pallet is heated to the proper temperature, to touch the end of this thread to it at the place where the shellac is wanted. With a little practice one can learn to deposit just the right amount. After the pallet is cold,allshellac on the surface should be cleaned off carefully with a scraper made of brass or nickel. THE JEWEL PIN ACTION The fork and jewel pin action involves two distinct functions: the impulse and the unlocking. In order to illustrate and make this statement clear, we will consider the different parts of the escapement in a normal position, as shown on page 34, Fig. 1. The hairspring, controlling the balance, has brought the fork, by means of the jewel pin, to the normal position of rest. This leaves the pallet in a position where the impulse face of an escape wheel tooth will engage the impulse face of one or the other of the pallet stones, in this instance the R stone. Assuming the parts to be in this relation to each other, it is evident that when power is applied to the escape wheel,the escape wheel tooth,which is engaging the R stone, will cause the pallet to t u r n on its pivots, and this impulse is transmitted to the balance by the fork acting on the jewel pin. The impulse being completed, the escape tooth drops off from the R stone, and the second tooth forward comes to lock on the L stone, with the fork resting against the banking, as shown on page 36, Fig. 3. The fork slot is n o w in such a position that the jewel p i n m a y pass o u t perfectly free, and this condition is necessary because the impulse which was given to the balance imparted to that member acertainmomentum,causingit tocontinuetoturninthatdirectionuntilthismomentum is overcome by the tension of the hairspring. During this part of the motion, which takes place after the impulse, the jewel pin leaves the fork entirely, but the instant that the momentum in the balance is overcome by the tension in the spring, the balance will start to t u r n in the oppositedirection, the tendency of the spring being to bring the jewel p i n to the center line. Before reaching this point, however, the jewel p i n has to perform the very important function of unlocking. At the completion of the impulse we left the fork resting on the banking, with the fork slot in such position that the jewel p i n passed out perfectly free, and, figuring on the assistance of the draft and the safety action, which will be explained later, we are justified in expecting that the jewel p i n shall pass in to the fork slot perfectly free. The instant the jewel p i n has entered the slot, and comes in contact 35 DOUBLE ROLLER ESCAPE‐ MENT with the fork, the work of unlocking begins. And here is to be noticed, that for every tick of the watch, the pallet and fork is started from the condition of rest,by a sudden blow of the jewel pin. And not only the pallet is started,butthe whole train has tobestarted in the reverse direction, against the power of the mainspring, to unlock the escape wheel, in order to receive another impulse. The impulse on the L stone being completed, the pallet assumes the position shown on page 22. The jewel p i n passing o u t on an excursion, the same as on the other side, returns to unlock, receives a new impulse, and so on, at the rate of 18,000 times per hour. In viewof the above,it is evident that lightness,as far as it is consistent with strength and wearingquality, is an essential feature in the construction of the several parts. It was once considered necessary to attach a counterweight to the pallet,in order to get it in poise,b u t with the modern light construction of pallet and fork, it has been proven beyond a doubt that the ordinary form of counterpoise was worse than useless, inasmuch as it involved an added mass of metal whose inertia m u s t be overcome at each vibration of the balance. 38 THE SAFETY ACTION The function of the safety action is to guard the escapement against unlocking from sudden shocks, or outside influences, while the jewel pin is out of engagement with the fork. In the lower grades of watch movements this guard duty is assigned to the edge of the table roller and the guard pin. The passing hollow, a small cut in the edge of theroller,directly outsidethejewel pin,allowstheguardpintopassthecenterlineduring the jewel pin action. This form of safety action is called “single roller” and is shown in plan and elevation on opposite page. As will be'seen from this drawing, the edge of the roller is made straight, or cylindrical, and the guard p i n is bent in such a way as'to present a curved portion to the edge of the roller. The advantage gainedfrom this construction is that the guard pin can be adjusted forward or back by simply bending it at the base, withoutitsactionbeingin anywayafiectedbyareasonableamountofendwisemovement Fig.1 I ! I SINGLE ROLLER ESCAPE- \ . MENT 40 of either the balance staff or the pallet arbor. The double roller escapement, Figs. 3 and 4, page 36,presents a more desirable form of safety action;for two reasons: first, the inter‐ section of theguard pin with the roller is much greater, making it perfectly safe against catching, or wedging; second, any shock, or jar, causing the guard pin to touch the roller, will have less effect on the running of the watch, because the impinging takes place on a smaller diameter. The diagrams, Figs. 5 and 6 on the opposite page,illustrate the above statements. Thewedgeactionoftheguardpin,whenitisbroughttotheroller,isrepre‐ sented by the lines C and D, which are at right angles to the lines A and B, thus forming tangents to the points of contact. It will be seen that with the single roller this wedge is 17°, whereas in the double roller.it is 30°, a very considerable difference in favor of the double roller. SAFETY ACTIONS Fm5 ‐‐ -‐ 5//VGLE 304LEI? Fig. 6 DOUBLE 5041m 41 DIRECTIONS FOR PUTTING THE ESCAPEMENT IN BEAT An escapement is said to be in beat when it requires the same amount of power to start the balance in one direction as in the other. This should be tried with the main‐ springonlypartlywoundup,byarrestingthemotionofthebalancewitha pointedobject held between the heads of two balance screws, and allowing the balance to move slowly, first in one direction and then in the other. If it appears to require more power,in order to let off on one side than the other, it is said to be “ o u t of beat,” and it should be corrected by turning the hairspring collet a certain amount, on the balance stafi, until it takes the same amount of power to let off on one pallet stone as on the other. This is usually done without removing the balance, by reaching in over the top side of the hairspring with a special tool made of small steelwire and flattened at the end soas to enter the slot in the collet. Great care should, however, be exercised in doing this work, so as to avoid bending the hairspring o u t of true. 44 TIME AND TIMING See the minutes how they run! How many make the hour complete, How many hours bring about the day, How many days will finish up the year. (Henry V I ) One revolution of the earth on its axis in relation to a fixed star has, on account of its perfect uniformity, been adopted as the standard for the measuring of time. We are told that three barleycorns make an inch, and that the distance from the Equator to the North Pole is very near 1,000,000,000 centimeters. But we know, positively, from the calculations of the eclipses that one revolution of the earth is made in exactly the same lengthoftimenowas2100yearsago,atleast,within72,0partofasecond. Sothehow]‐ ogist m a y feel justly proud of having such a perfect standard for his work. And about him, it might be said, without exaggeration, that he is hitching his ideal to a star. The time occupied by the earth in making one revolution on its axis, in relation to a fixed star, is called a sidereal day, and is about §%,'§ shorter than a mean solar day. This difference is caused by the earth’s travelling around the sun once a year, in what might be called the same direction asit revolves on its axis. This, from our point of view, makes the sun lose one round in every 366, as compared with the fixed stars. True sun time is the time occupied by the earth in making onerevolution on its axis in relation to the sun,‐that is,frommiddaytomidday,asthesunpassesthemeridian. Thedurationoftheseintervals vary duringtheyear,because theearth’s orbit aroundthesunisnot circular, but elliptical, with the sun in one of the foci. The earth travels faster when it is in the part of this orbit which is nearest the sun, on accountof the greaterattraction of that body, and the varia‐ tion of time during a year from this cause is as great as seventeen minutes plus or minus from mean time. Mean time is obtained by dividing a whole year in as many equal parts as the number of solar days it contains; and if we take one of these mean solar days 45 of 86,400 seconds for a comparison, the sidereal day is 86,164.09 seconds long, or exactly 3 minutes 55.91 seconds shorter than