HOROLOGY. 



131 



bor, or cylinder, being notched or cut across into the 

 centre, allows the wheel of arrfie to pass, and the 

 wheel of impulsion, after getting a small recoil, gives 

 new force to the vibration ; <o that in two vibrations 

 only one of them is accelerated : Hence it was thought, 

 that the half of the vibrations being/rrr, and indepen- 

 dent of the wheel work and its inequalities, they would 

 be more correct than others ; but experience did not 

 confirm this." This is, then, the duplex 'scapement, or 

 the nearest possible approach to it. 



It is IT ore than fifty yean since we saw a small spring 

 dock havirg this 'scaprment, made by a very ingenious 

 clockmaker of this place, whose name was Robert Brack- 

 enrigg It may be supposed to have been made a very 



e-ars after Thiout's work was published. 



1 737, Peter le Roy gave an account of a 'scape- 

 ment which he had made, having one pallet on the 

 axis of the balance and a notch Iwlow it, a wheel of ar- 

 rear, and one o/ impulse, as described in the preceding 

 an that one- half of the vibrations were in- 

 Dt of the wheel-work. Dutertre claimed the 

 pretended invention of Le Roy, who, finding it not to 

 sssswtr his expectations, gave it up. 'lint Dutertre 

 made the one which is represented in Plate xli. of 

 Thiout, we have no doubt ; and there is unquestion- 

 able authority, that he brought Dr Hooke's to the im- 

 proved state which has just been mentioned. It is 

 aid, that be had made a free or detached ' scapement; 

 but no account whatever has been given ot 



The duplex 'sespemtpt. as it is now called, was in- 

 tfodocedinto its native country about thirty years ago or 

 more, under the name of Tyrer s scapement. the name, 

 it is supposed, of him who put the last band to im- 

 prove that which came in a lineal dears nt from Dr 

 Hooke. In place of the notch being made right acruas 

 the arbor, as has been mentioned before, Tyrer's had a 

 very small cy under or rniler, whose diameter was .CW of 



tioo. a deep angular notch of 3O or K> degrees. The cy- 

 linder was sometimes of steel, but most frequently ot ru* 

 by. When the points of the teeth of the wheel of rap 

 fall into the notch, they meet with a ve 

 by the balance, in what may be called the returning 

 vibration. This goes so far as to make the point of the 

 teeth for a little to leave the notch, at the side opposite 



to (Jiat l<\ hu h It CAT! 1 '- : II 1 !'r *v. ! inre T: n '. . r : . r. /. 



is now in the coarse of that vibration when it is to 

 receive impulse from the wheel, which 



'.,,., 



in 



of 



aethe 



alae escapes from the pallet. the next tooth of 

 falls to rest on the small cylinder, and so on. 

 'This 'scapement of Tyrcr's is much superior to that 

 of the cylinder, or boruontal one : it is almost inde- 

 pendent of oil, requiring only a very little to the paints 

 of the wheel teeth of repose. It can carry a balsa rr 

 of much greater miisasntnas. and. when well executed, 

 (ififiBBM most admirably. But there are so nun \ 



or minutiai. to be atfcailul to in it,' that 

 of them wary at times escape the rye of the mo* 

 aweful ; the watch may stop, and yet the 



Why should they not be made as thick as the pallet of * 

 detached 'scapement? There is no 'scapement which 

 requires to have the balance wheel teeth more correctly 

 rut. i .r the steady pins of the cock and potencp more nice- 

 ly fitted to their places in the potence plate. The minu- 

 tiae alluded to were, too much or too little drop of the 

 impulse teeth on the pallet, the 'scapement not set quite 

 so near to beat as might be, the balance rather heavy, or 

 the points of the teeth of repose too much or to little in 

 on the small cylinder. Ins good sizeable pocket watch, 

 the wheels having fifteen teeth, the ratio of the diameter 

 of the wheel of repose to that of impulse may be as .520 

 of an inch to -400, the cylinder .030. The angle of 

 'scapement will be 60 degrees, taking from the escape 

 of the impulse tooth, to that of the tooth of repose fal- 

 ling on the cylinder ; the balance passes 20 of these, 

 before the impulse tooth gets again on the pallet, con- 

 sequently it IMS only 4O degrees for the acting angle 

 of the 'scapement. There u a variety of 'scapemenU 

 in Berthoud's Hutoire, which appeared in 1802, many 

 of which are of very inferior note to that of Tyrer's, and 

 yet be takes no notice of the latter. This is remarka- 

 ble, as he Mirely must hare seen it, considering the great 

 number of them which were made. 



While Dutertre was engaged with Hooke's 'scape- 

 ment, an artist in England, whose name is unknown, pro- 

 duced a 'scapement with the dead beat, which seems at 

 thattime to have been the great object of pur-nit. .In- 

 lien Le Roy having got one of these watches, showed it 

 to Solly in November 1787, and told him that it was a 

 scaprment very deserving of notice. Tliiout in. ntion- 

 it as a 'scapement of M. Flameii ville having two pallets 

 of repose ; and says that rt bad much attracted the atten- 

 tion of the English watch-makers, who had made it I'ur 

 three orfinir years. (See page 108, plate xliii. fig. 6. of 

 his first volume.) With our workmen it went i 

 name of the 'tcapernent with the tumbling pallets.' The 

 axis of the balance had two semi-cylindrical pallets, 

 whose faces stood in the same plane or centre 

 axis; the balance wheel was the common crown wheel 

 one, the teeth of which got a very small hold ot the 

 pallet*. When exaping from the face of one pallet. A 

 tooth on the opposite side dropped on the semi-cy limlri- 

 cal part of the other pallet, where it rested during the 

 going and coming of the vibration ; getting then on the 

 tuff, it gave new impulse, escaping in its turn ; the pal- 

 let on the opposite end of the verge received a tooth on 

 the semi- cylindrical part, and so on. After having been 

 hid aside far son* time, it was of late years taken up 

 by several, who no doubt must have thought well of it. 

 Among these was Kendal, a man possessed of no com- 

 mon talents. He transformed it into one having two 

 crown wheels on the same pinion arbour, die tops of the 



top, and yet the 

 M complete M 



be in every on 



This has often given the wearer cause to 

 and to suspect the qualities of his watch, 

 i watchmaker* have been induced to abandon 

 this 'icapeaient, and adopt inferior ones. The pallets 

 f Tyrer's were at first very thin. We frequent 

 ged the nsussiri of having them made much t> 

 and were pluasrd to see that this was gradually adopted. 



Esrapr- 



mtnts. 



with mni- 

 cylir.dricml 

 or tumbling 

 pcllcu. 



Pi ATI: 

 mil. 

 Pig. 9. 



Kmi'sl'i 



',i..; ...i' 



teeth in the one pointing to the middle of the spaces 

 in the other, and with only one pallet, the diameter of 

 the srraiey Under being of any *ie. (See Plate IVf I 1 1 . 

 1 IK I.) AUut thirty years ago we had tome watchen 

 made w it li this 'urapcinen t , and after a few years trial 

 gave them up. The principle of the 'scapement is 

 good, as long as the parts of it remain unimpaired, 

 and the oil continues fresh ; but the acting parts hav- 

 ing each a small hold of one another, get soon altered, 

 which causes a great deviation from the rate of time 

 ith which it first sets out. They cannot be expected 

 to last Inc. unless with a diamond pallet, and a steel 

 wheel of the hardest temper. 



The frtf or , . apem'*t is that in which the 



greater part of the vibrat , balance in free and 



independent wf (be wbech, the balance wheel being 



PLATE 



((i 111. 

 rig- 1. 



