WATCH. 



fpring /, beyond the centre of motion i ; and at this inftant 

 the bar /, afcending alfo, quits the teeth of the efcapement- 

 wheel, and fuffers the alarm to comnrience, and to continue 

 until the warning-fpring is relaxed. It does not, however, 

 appear by what means the pin of the hours- wheel is difen- 

 gaged from the oblong hole in the fteel circle of wheel m, 

 when the blows of the hammer are finifhed, unlefs the fecond 

 edge of the flit be made floping ; and its continuance there 

 muft obvioufly flop the watch, by preventing the free pro- 

 grefs of the hours-wheel. Either the mechanifm or the 

 original defcription muft be defeftive in this part. Within 

 the ring of the pendant is a button, in form of an 

 acorn, which conftitutes the head of a fteel arbor, termi- 

 nating with a pinion s, that aftiiates a contrate-wheel o, 

 which has teeth alfo on the edge, that drive the double 

 pinion p ; the upper portion of which pinion again impels 

 the large wheel m, that carries the fmall hand, and alfo the 

 circular piece of notched fteel. This train is introduced 

 for the purpofe of fetting the warning-hand, which is the 

 fhorteft of the three feen \n Jig. 12, to the requifite hour on 

 the fmall fixed dial, without opening the cafe, and de- 

 ranging the other hands for fhewing hours and minutes in 

 the ufual way. At the bottom of the acorn there is a fmall 

 ratchet-wheel, with a click and fpring, feen detached be- 

 tween ^^x. II and 14, the ufe of which is to allow the 

 acorn to turn only in one direftion, while the warning-hand 

 is fet to its place. It is a condition to be obferved in fet- 

 ting the hour-hand, that it lie exaftly over the pin in the 

 hourscwheel, and alfo that the warning-hand lie parallel to 

 the Jlit of the fteel circle, attached to the wheel m. Laftly, 

 the warning mechanifm may be put into a ftate of acflion, or 

 of inaftion, by moving the button v, in the cafe, to the 

 right or left, fo as to fall in the way of the end of the 

 detent /, or to efcape it. 



Rolling Watch. — After having defcribed various conftruc- 

 tions of watches adapted for the pocket, and contributing 

 to the punftuality with which focial intercourfe is carried on 

 in civilized life, we proceed laftly to defcribe the mechanifm 

 of a watch, which wiU meafure time only by its defcent 

 down an inclined plane, and which therefore is more curious 

 than ufeful. During the time that various experiments on 

 the laws of moving bodies were made, and applied to the 

 regulation of horological machines by Dr. Wallis, fir Chrif- 

 topher Wren, Dr. Hooke, Huygens, Leibnitz, Dr. Hal- 

 ley, fir Ifaac Newton, and others, M. de Gennes and the 

 marquis of Worcefter contrived watches, the former of 

 wliich would ajcend, and the latter defcend along an inclined 

 plane, by means of a fpring coiled up at the centre of the 

 frame, which relaxed as the rolling motion proceeded ; but 

 as no explanation had been given of thcfc contrivances in the 

 year 1684, Mr. Maurice Wheeler publiftied an account of 

 a rolling watch, invented by him, in the firil volume of 

 Lowthorp's Abridgment of the Philofophical TranfaAions 

 of London, p. 468, et feq., which account has been co- 

 pied into other works of fcience ; but which we will 

 abridge, agreeably to our own plan of defcription. In 

 f.g. 15. Plate XLIV., let a i be the diameter of the cir- 

 cle afb h, ftanding on the dotted horizontal bafe b m, on 

 the point b. In this fituation, fappofingthe circle to be an 

 uniform plate of metal, jt will remain at reft when placed 

 truly vertical, while the line b m remains horizontal ; but 

 make this line to coincide with the inclined line n b, and the 

 circle will roll down this inclined plane, becaufe the vertical 

 line, or line of direftion, d e, raifed from the point d, which 

 will be the nev? point of contact, falls behind c, the centre 

 of gravity of the uniform circular plate ; fo that the por- 

 tion efd becoming fmaller than the portion e h d, the cen- 

 10 



tre of gravity will be before the bearing point d, and the 

 plate will roll down the plane ; and the motion thus pro- 

 duced will have the greater velocity, the more the plane n b 

 is inchned to the horizontal line. But if fuch a piece of 

 metal ^ be attached to the portion efd3.% will form a coun- 

 terpoife therewith to the larger portion e h d, then the plate 

 will have no tendency to roll, but become ftationary, fo long 

 as the inchnation of the plane, and the pofition of the addi- 

 tional piece g, remain unaltered ; but lefTen the angle of in- 

 clination, or remove the weight g towards f, and, in either 

 cafe, the plate will aftually afcend, till the weight g, in its 

 new pofition, balances the^new angle of inclination. Alfo, 

 if the angle be increafed, or tjie weight g be brought nearer 

 to d, in either cafe the plate will defcend ; but as the defcent 

 of the plate down the increafed inclination, by a rolling 

 motion, throws the weight g farther from the point of con- 

 tadl d, the rolling motion will ftop as foon as the retrograde 

 motion of the weight fhall have produced a counterpoife to 

 the portion e h d of the plate in the new inchned plane. 

 Thefe premifes being granted, we are now prepared to (hew 

 how the train of a watch in motion may be made to change 

 the pofition of an appended weight in fuch way as to render 

 that weight a maintaining power during the whole time that 

 a cylindrical box, which contains the weight and movement, 

 fhall gradually and flowly defcend down a con-efponding in- 

 clined plane, while a pendulous hand or index ftiall point 

 out the fucceffive hours and parts during the faid defcent- 

 Let the four wheels and pinions, fliewn mjig. 1 7) be placed 

 like the common train of a watch, with the arbor x of the 

 great wheel in the centre of the box, and conceive a ba- 

 lance and efcapement to allow one tooth of the laft wheel to 

 efcape at every alternate ofcillation of the moving balance ; 

 then let the weight w, at the end of the lever x iv, be made 

 faft to the faid arbor at the hole x, Jig. 16, as is feen in 

 Jg. 17 ; and let its pofition be between (/andy"; and the ten- 

 dency of the weight w to come to d, will draw round the 

 great wheel, pivotted to the ends of the box, and give fuch 

 motion to the train as will keep up the ofciUations of the 

 balance ; but this motion of the great wheel will be fo flow, 

 that it will be fcarcely perceptible when the angle of incli- 

 nation is fmall ; but increafe this angle, or alter the pofition 

 or the magnitude of the weight, and the force will be in- 

 creafed by which the train is aftuated ; fo that by one al- 

 teration or other, or all, fuch a final adjuftment may be 

 made, that the box will revolve exaftly in twenty-four 

 hours. But before this can be duly effedled, the train of 

 wheels muft be counterpoifed by a load, attached to the box 

 at the oppofite fide of the centre, fo that there may be one 

 common centre of gravity of all the materials, exclufive of 

 the weight <w, falhng in every pofition of the box, at the 

 centre of motion of the weight w ; ;'. c: at the arbor of the 

 great wheel round which the box revolves. Wheii this is the 

 cafe, and the angle of elevation of the plane is nicely ad- 

 jufted by a fcrew A, as in Jg. 18, the regulated train of 

 the watch will allow the weight to to approach d, juft as 

 faft as the rolling motion of the box will throw it back, 

 and the equipoife of thefe two contrary a<Elions of gravity, 

 and of the rotation of the box produced thereby, will keep 

 up an uniform flow motion down the inclined plane. In 

 fome conftruClions detailed in the " Recueil d'Ouvrages 

 curieux de Mathematique et de Mechanique ; ou Defcription 

 du Cabinet de Monfieur de Serviere," a Lyon, 1733, the 

 hours are drawn on the face of the inchned plane, and indi- 

 cated by the point of contaft of the box ; but in the watch 

 before us, one end of the box contains the figures from I. to 

 XII. twice over, and a pendulous hand, made heavy below, 

 and revolving loofely on the pivot of the great wheel, 



always 



