CHAMBERS'S INFORMATION FOR THE PEOPLE. 



Teal improvement was made by George Graham, 



the inventor of the 

 dead escapement in 

 clocks. This is 

 called the horizontal 

 escapement ; it was 

 introduced in the 

 beginning of the last 

 century, and it is still 

 the escapement used 

 in most foreign watches. The impulse is given to 

 a hollow cut in the cylindrical axis of the balance, 

 by teeth of a peculiar form projecting from a 

 horizontal crown-wheel. Other forms of escape- 

 ment in high estimation are the lever escape- 

 ment, originally invented by Berthoud, improved 

 by Mudge ; the duplex escapement, the principle 

 invented by Hooke, the construction perfected by 

 Tyrer ; and the detached escapement of Berthoud, 

 improved by Arnold and Earnshaw. The last- 

 mentioned is that which is employed in marine 

 chronometers and in pocket-chronometers, as 

 watches made in all respects like chronometers 

 are called. The lever escapement is that which 

 is used in most English watches. In it the scape- 

 wheel and pallets are 

 exactly the same as 

 in the dead escape- 

 ment in clocks. The 

 pallets, p, p, are set 

 on a lever which 

 turns on their arbor, 

 A ; and there is a 

 pin, B, in a small 

 disc on the verge or 

 arbor of the balance, 

 which works into a 

 notch at the end of 

 the lever. The pin and notch are so adjusted, 

 that when a tooth of the scape-wheel has got free, 

 the pin slips out of the notch, and the balance is 

 detached from the lever during the remainder of 

 its swing ; whence the name detached lever escape- 

 ment, originally applied to this arrangement. On 

 the balance returning, the pin again enters the 

 notch, moving the lever just enough to send the 

 tooth next in order to escape from the dead face 

 of the pallet on to the impulse face; then the 

 scape-wheel acts upon the lever and balance ; the 

 tooth escapes, and another drops upon the dead 

 face of the pallet, the pin at the same time passing 

 out of the notch in the other direction, leaving the 

 balance again free. This arrangement is found to 

 give great accuracy and steadiness of performance. 

 To prevent the teeth from slipping away while the 

 balance is free, the faces of the pallets are slightly 

 undercut, and this makes them secure while at 

 rest ; moreover, there is a pin on the lever which 

 moves through a notch on the balance disc, while 

 the pin, B, moves through the notch in the lever, 

 which is so adjusted as to guard against the lever 

 moving and the teeth escaping, while the balance 

 is free. 



Balance and Balance-spring. 



These are the only other parts of the mechanism 

 of the watch of which it is necessary here to treat. 



The balance, as may be seen from the represen- 

 tations of it in connection with the different escape- 

 ments just noticed, is a wheel finely poised on its 



axis ; the pivot-holes in which it turns being fre- 

 quently in chronometers and clocks, as well as 

 in watches jewelled, or made of small rubies, 

 diamonds, &c. ; as those of other of the wheels 

 also are, for the sake of durability. The natural 

 effect of an impulse given to such a wheel would 

 be a complete rotation on its axis. This, however, 

 as we have already seen, is convertible, by various 

 escapements, into a vibratory motion. But as in 

 clocks the pendulum was found to be a most 

 invaluable adjunct, absorbing, as it were, in its 

 own more or less extended oscillation, every in- 

 equality in the rotation of the wheel-work, or the 

 vibration of the balance, something of precisely 

 the same nature for watch-escapements was the 

 great desideratum, when the balance-spring or 

 hair-spring was invented ; and, from this analogy, 

 it even acquired, improperly, the name of the 

 pendulum-spring.* 



Simple and obvious as the suggestion of the 

 regulative influence of a spring, applied to the 

 vibrating mechanism of the watch-balance, in 

 place of either weight or pendulum, may now 

 appear especially after the idea of the mainspring, 

 as a substitute for the maintaining weight, had 

 been suggested this has been held to be a crown- 

 ing invention in the mechanism of the watch ; and 

 the honour of its first suggestion has been claimed 

 by no less than three very eminent men by Dr 

 Hooke ; by Abbe* Hautefeuille, a Frenchman ; and 

 by Hiiygens, the Dutch astronomer. It was ulti- 

 mately proved, that although Hiiygens had applied 

 for a patent at Paris in 1674, Hautefeuille had 

 done so several years before ; while Hooke had 

 made a similar application in England in 1658. 

 To Hooke, therefore, must be attributed the first 

 idea of the balance-spring. 



In its application to the balance of a watch, one 

 of the extremities (<?) of the spring 

 is fastened to a point independ- 

 ent of the balance, while the 

 other is attached near its axis. 

 When the balance is at rest, the 

 spring is inclined neither way, 

 this position being called the 

 point of rest ; but when the 

 impulse is given to the balance 

 by the crown-wheel of the escapement, it is clear 

 that now a rotatory motion of the balance cannot 

 take place, even though there should be nothing 

 in the form of the escapement to prevent it ; the 

 balance will now only move round so far as the 

 impulse given is able to overcome the elastic 

 resistance of the spring ; and when that resistance 

 becomes equal to the impulse given, the balance 

 will stop for a moment, and then be driven back 

 by the elastic recoil of the spring, continuing thus 

 to vibrate so long as the impulse is repeated or 

 the watch is in motion. 



The recoil of the spring is sufficient to drive back 

 the balance to a distance nearly double the length 

 of its first motion ; this is therefore called the long 

 arc of vibration. But when the motion of the 

 balance is free, with a certain length of spring, 

 the long arc of vibration is made in less time than 



* This little instrument, the hair-spring, is no less remarkable 

 for the extreme delicacy of its construction, than for the great 

 value which it shews the possibility of giving to a piece of steel, 

 of exceedingly small and insignificant appearance, by manual 

 labour. Four thousand hair-springs scarcely weigh more than 

 a single ounce, but cost often more than .1000 ! 



