HOROLOGY. 



151 



V :.-. 



p,i.hcr ha* brought back and stt aside all the pieces 

 which communicate with the snails L, X : for at this time 

 t communication t.r connection between the 



pieces of the movement and those of the motion work, 

 Imt t'.iat of the pin O of the snail or surprise, with the 

 ie star wheel E, which nothing can prevent 

 from retrograding. If then the minute hand is made to 

 make a complete turn backward, the pin O will also 

 make one of the teeth of the star to retrograde; and if the 

 watch M made afterwards to repeat, it will strike al- 

 ways the hours and quarters as marked by the hands. 

 But it must be observed, that if the bands were turned in 

 the same instant that the watch is made to repeat, they 

 would then be prevented : it i necessary then, before 

 !, hands of a repeating clock or watch, to 

 wait till it lias repeated the hour, so that all the pieces 

 shall have taken their natural situation*. 



It i< easy to conclude from this, that since with a 

 repeating watch, we can set backward or forward the 

 minute hand, according as it may be required, we may 

 with much greater reason do this in a plain watch, 

 whr* no obstacle is opposed to it. 



As to the hour hand of a repeating watch, it ought 

 never to be turned without that being done by the 

 minute hand alone ; except in that race where the re- 

 peater does not strike the hour marked by the hour band, 

 when it would be necessary to put it to the hour which 

 the repeater strike*. 



When the repeater get* of itself deranged, by the 

 hour hand not according with the hour nhiih the watch 

 strikes, this is a proof that the jumper S, or the | 

 of the snail, do not produce well the effect they ought 

 to have. 



The returning 

 tarns on the it. 

 cannon pinion X 



cannon pinion then make 



torn* whilst it makes one ; this carries a pinion of ten 

 teeth, which pitches or lea<Utl>e hour wheel, Fig. 7. which 

 has forty ; the wheel. Fig. 8. makes then fear turns 

 far one of the hour wheel ; the cannon pinion 



or edge of the pillar plate, is sunk a little way, with Repeating 

 which it is kept fast by means of keys, or griffs 13. and NVatclics 

 14. The brass edge is covered by the dial, fixed alter S ""Y" 1 

 that of the brass edge, by means of a screw. 



A repeater is made to strike the hour which it in- 

 dicates the moment we press in the pendant; so that 

 the machine must be contrived in such a way, that it 

 may be easy to push in the pendant, and that the blows 

 of the hammers may be the strongest possible. With 

 respect to the first, that depends on two things; the given 

 force of the spring, and the length of the pu-her ; that 

 is to say, the space described, and the manner of making 

 the pusher act on the rack. With regard to the lust, the 

 rack must be placed in such a manner, that the point 

 of contact of the pusher follows the arc described l>y 

 the rack, in such a way that the force shall not be de- 

 composed, so that the action of the hand on the push- 

 er shall act wholly upon the rack. 



With regard to the pusher, its length depends on the 

 point where it acts on the rack ; that is to say, accord- 

 ing as it acts farther or nearer the centre of motion. It 

 is obvious, that if it acts near the centre, more force 

 is required, and it will describe a les* space, and 

 nee rersa. As to the force of the blow of the ham- 

 mer, it i liniititl by the I'orce of the repeating main- 

 spring, snd by thcfonv tli it the runners require to move 

 or keep them in motion ; for it is clear, that it is only 

 the execs* of the force of the spring over the resistance 

 of these wheels, that can be employed to raise the ham- 

 mer. The nuiuix-r of blows of the hammer, for one 

 revolution of the ratchet, determine* again the force of 

 the blow. 



the 

 ch has twelve teeth ; the wheel, 



qooatly makes twelve turn* for one of the hour wheel, 

 awl the cannon pinion make* one torn in an hour ; the 

 hour wheel takes then twelve hows to make one revo- 

 lution ; it is the socket of the hoar wheel which carries 

 the hour hand. The raising or lifting piece m. m, 1 

 cm only describe a small arc, which permit* the ratchet 

 R to retrograde ; and so soon a* the mover bring* it 

 back, the arm 1 of the raising piece draw* the ham- 

 Figure 5. r|ii aunts the under aide of the all or no. 

 >th the two stud*; one * a* a centre on which 

 k movrt, and the other * on which the star and snail 

 the hole of this piece allow* the aosjam 

 of the fusee of the movement to come through, and 

 lastly passing through the dial, serve* for winding up 



; and bolt. 







the watch. W . the locking 



t'lM 1* W *| I ' Drt'tfT**) *}*' l''l)*"l*l*Tl* * 



't tfi r.iM'. 



Y is a small cock or bridge which keep* the rack to 

 its place, and prevents it from getting away from the 

 plate, prrmittine. k to turn onl 



y on it* own centre. 



. 



All the parts of the repetition or motion work, which 

 has been described, ate placed on the back of the pam* 

 plate, and are covered by the dial ; so that between the 

 plate ( Fig. S. ) and the dial shore must bean interval, to 

 allow suAoent play for the motion-WMk : It is for thi 

 purpose that a piece is destined, wrn. 



Mil here, and which is called the bnua edge. This 

 sort of circle, or ring, into which the dmiaftimce, 



( MAP. IV 



O* 



Pendulumt. 



u a 



COMPENSATION Pendulums are those which are con- rnmpsnts 

 ttructad to taasjtaratt the effect of heat and cold, in """ i*ndu- 

 lengthening or shortening a pendulum rod. lunu - 



J'roi Won<l-linii, canon of Condi in Flanders, 

 who published a dissertation, in Hi'.'li, on the obliquity 

 of the eclipbc, teems so have been the first who obser- 

 ved that, by change of temperature, metals changed 

 their length*. 



Graham was the first person who thought of making Fim <ug- 

 a pendulum rod that should cuuntanM the effect* of atcd b r 

 heat and coM on it. by a combination of rods or wires ' , 'I? 

 of different metals, tuch a* bras*, tilvrr. Mrel, \-c. ; but '" 

 he never put it in execution, from the opinion that it 

 would not be effectual enough in its operation*. It oc- 

 curred to him at thr same time, that mercury, from its 

 great expansion by heat, would be morr adapted to the 

 end he wa< in pursuit of. Having made a pendulum on 

 lhi principle, it was applied to a clock, and set a-goinc. 

 It it described in the /MrfotopAira/ Tramaftiont. 

 999, in a paper which was given into the Socirt 

 1726'. He say*, " thr clock was kept continually go- 

 ing, without having either tlir pendulum or the hand* 

 altered, from the <)th June 1722 to the 14th Xovember 

 l-eing three year* ami I'mir month*." Some time 

 previout tr. I irrinon being then at Harrow in 



Lincolnshire, wa* engaged in making rx|><Tmirnts on 

 bra** and steel rod, with the same vi< , nn.l produced 

 what i now cal 1 t) r . 



tcripiioH oflno Melhodi, SfC. by John Kllicott. I 

 London, 1 1 Kmn 



Some astJMts may be formed of tin- advantages of ,;,,,], p^,. 

 a comnrmation pendulum, by comparing thr going of dulumi. 



