Jlfi 



HOROLOGY. 



CHAP. I. 



On the Escapement, or ''Scapement. 



t'ii 1-C.ljT 



ments. 



Crown 

 wheel and 

 verge 



THE escapement is that part of a clock or watch 

 connected with the beats which we hear them give ; 

 and these beats are the effects of the moving power, 

 carried forward by means of the wheels in the move- 

 ment to the last one, which is called the swing wheel 

 in a pendulum clock, and the balance wheel in a watch. 

 The teeth of this wheel act on the pallets or verge, 

 which are of various shapes, and which form the most 

 essential part in a 'ecapement ; the drop from eacli 

 tooth of the swing or balance wheels, on their respec- 

 tive pallets, giving one beat or impulse to the pendu- 

 lum or balance, in order to keep up or maintain their 

 motion ; and were it not for the pallets which alter- 

 nately stop the teeth of the swing or balance wheels, 

 the motive force would hare no check. Hence it is, 

 that, by this mechanism of the 'scapement, the wheels 

 in the movement are prevented from having their re- 

 volutions accelerated, which would take place to such 

 a degree, as to make the machine run down in a mi- 

 nute or two; whereas, from the resistance opposed by 

 the pallets, it is kept going for twenty -four or thirty 

 hours, for a week or a month, or even for twelve 

 months. In the clocks or watches, however, which as 

 a matter of curiosity have been made to go so long, it 

 was not possible to have an accurate measure of time. 

 No part of a clock or watch requires so much skill 

 and judgment in the contrivance of it, and so much care 

 and nicety in its execution, as that of the 'scapement ; 

 'scapement. none o f ^ ne 'scapemcnts of the present day require 

 this more than the ancient crown wheel and verge 

 'scapement, which when nicely executed, upon the pro- 

 per principle, does extremely well for a common pocket 

 watch. But this is a thing hardly now to be met with. 

 From the time of Dr Hooke, and during the last cen 

 tury, many ingenious contrivances for 'scapements 

 were suggested ; but the number of them adopted in 

 practice is very limited. The crown wheel and verge 

 'scapement is represented in Fig. 2, where V is the 

 verge and C the crown wheel, p, p the pallets, and BB 

 the balance. It is the oldest that is known, and must 

 have been the only one used in clocks, for several 

 centuries, previous to the middle of the seventeenth, 

 or towards the end of it. Although it has been 

 so long in use, and so well known to every clock 

 and watch-maker, that its merits are now overlooked, 

 and held in little estimation, yet, if it is duly consider- 

 ed, it will be found to have been a very masterly and 

 ingenious device. The crown wheel and verge are of 

 such an odd shape, that they resemble nothing that is 

 familiar to us. Yet some ancient artist had contrived 

 it for the purpose (and it certainly was an ingenious 

 thought) to give an alternate motion to a plain wheel, 

 or cross, which he had suspended from the upper end 

 of its axis by a string, or which at first might rest on 

 the lower end of the axis or foot pivot. This plain 

 wheel was like the fly of our 'common kitchen jack. 

 In place of this circular rim, or plain wheel -on the 

 axis, there were some of them that had two arms upon 

 it, forming something like a cross ; on these were made 



PLATE 

 CCC. 

 Fig. 2. 



a sort of notches, concentric to the axis, in which were Escape- 

 hung a small weight on each arm, which, by shifting mcnts - 

 more or less from the centre, the clock was made to go -"V" 

 slow or fast. From the weightiness of this kind of 

 balance, and the rude execution of the work, the fric- 

 tion on the end of the foot pivot would be so great that 

 it is probable there was some difficulty to make the 

 clock keep going for any length of time. Recourse 

 was then had to suspend the balance by a small cord, , 



so that the end of the lower pivot should not rest on 

 the foot of the potence. This ingenious idea has in, 

 modern times been adopted both by Berthoud and Le 

 Roy, who have had the balances in some of their ma- 

 rine time-keepers suspended by a very small wire, or 

 a very delicate piece of watch pendulum spring wire. 

 The mechanism of the movement of these old clocks 

 is exactly the same as has been frequently made for an 

 alarm. To construct this, and apply it to a clock, there 

 was hardly a step to go ; and therefore in all probabi- 

 lity the invention of the alarm part took place before 

 that of the striking part, though some have thought 

 otherwise. The contrivance of the striking part was a p tATr 

 more complex process, and less likely to take place.* ccc. 

 The alarm-clock is represented in Fig. 3. Fig. 3. 



This opinion is strongly corroborated by the observa- 

 tions of Hamberger in Beckmann's History of Inventions. 

 " These horologia," he remarks, " not only pointed out 

 the hours by an index, but emitted also a sound. This 

 we learn from Primaria Instituta Canonicorum Prce- 

 monstatetilium, where it is ordered that the sacristan 

 should regulate the horologium, and make it sound be- 

 fore matins to awaken him. I dare not, however, ven- 

 ture thence to infer, that these machines announced the 

 number of the hour by their sound, as they seem only 

 to have given an alarm at the time of getting up from 

 bed. I have indeed never yet found a passage where 

 it is mentioned that the number of the hour was ex- 

 pressed by them ; and when we read of their emitting 

 a sound, we are to understand, that it was for the pur- 

 pose of awakening the sacristan to prayers. The ex- 

 pression horologium cecidit, which occurs frequently in 

 the before-quoted writers, I consider as allusive to this 

 sounding of the machine. Du Fresne, in my opinion, 

 under the word Horologium, conceives wrong the ex- 

 pression de prmderibvs in imitm delapsis, because the 

 machine was then at rest, and could raise neither the 

 sacristan or any one else, whose business it was to beat 

 the scilla," 



When an alarm is set off, the weight, which is the 

 moving force of it, very soon falls to the bottom, and 

 then the alarm ceases. 



In attempting to make the first 'scapement, there 

 can be little doubt that something of the circular or cy- 

 lindrical kind was contrived, and the only thing which 

 could give it an alternate motion, was either a spiral 

 spring or a pendulum ; but these things being then un- 

 known, the clockmaker was obliged to seek after other 

 methods, and at last produced the crown wheel and 

 verge 'scapement. How came it that means so compli- 

 cated were fallen on, when those which were more 

 simple and better were overlooked ? 



It is a very singular circumstance, that a small Discovery of 

 ball or weight, when suspended by a slender thread, the pcndu- 

 and drawn a little aside from the perpendicular, on 



* In many parts of India, where public clocks are unknown at this day, they strike the hours upon a plate of silver, or silver al- 

 loyed with another metal, of a lenticular form, about 18 inches in diameter. It is hung on a frame by a doubled string ; and when 

 the hour is pointed out, cither by their sand-glasses, clepsydra;, or water-dropping instruments, which they sometimes use, they strike 

 with a wooden hammer on the middle of the circular plate, and thus indicate, by the number of blows, the hour of the day. The 

 sound which is produced is strong, clear, and pleasant. This contrivance is used in many of the towns and camps throughout India. 



