123 



HOROLOGY. 



wire. Watches having the cylinder 'scapement were 

 not known in Fr.nK-e till 1728, when Julien Le 

 Roy commissioned one of them from Graham. They 

 were losing their character here, some time before the 

 introduction of the duplex, which contributed after- 

 wards still more to bring them down. The duplex will 

 in its turn be supplanted, for reasons which will be 

 afterwards noticed. Flat movements, shallow balance 

 wheels, steel and brass of l,.ul materials, from the diffi- 

 culty of getting them good, injudicious execution, and 

 low prices, must have tended to make thecylinder 'scape- 

 ments so bad as they were of late ; many of the cylinders 

 were destroyed and cut to pieces in a very few years, and 

 some of them could not last so long. Let these be 

 compared with the cylinder 'scjipements of old Hull, 

 many of which that we have seen, have little or no im- 

 pression even on their edges, after having been in 

 use thirty years and upwards. Of what did Hull's art 

 consist ? There must have been some causes for it ; 

 but what these are, we shall not attempt to conjecture. 

 As Graham, with whom he was instructed, did, Hull 

 soldered in the plugs of his cylinders, with silver sol- 

 der, which caused a very tedious process afterwards in 

 making the cylinder ; but this is not offered as any rea- 

 son for his excelling in the art of cylinder 'scapement 

 making. The acting edges of the teeth have hitherto 

 been made too thin, particularly for steel'cylinders, with 

 the view of lessening the friction ; but, from cutting 

 soon, this friction increased, and was worse than a 

 greater friction which was constant 



When the vibrations of the balance are at the lowest 



Eoint, the resistance of the pendulum spring is at the 

 :ast ; but the more it is bent or unbent, the greater is 

 the resistance ; consequently, when at the height of the 

 wedge or tooth, it is greater than when the tooth first 

 begins to act. Two or three different curves for this 

 purpose have been imagined; one approaching nearly 

 to a right line, which is supposed to give the wheel 

 time to acquire a velocity during the passing of two- 

 thirds of the curve, and the least resistance of the 

 spring, by which the other third more readily over- 

 comes, when the resistance to it is at the greatest. 

 This has been thought to give a greater extent to the 

 arc of vibration, and has been adopted by the French 

 artists. Another curve, where equal spaces make the 

 balance describe equal portions of a circle, is thought 

 to give the least wearing to the edges of the cylinder, 

 and is that which is practised by our 'scapement mak- 

 ers. Arguments equally good for either, it appears, 

 might be given. 



The weight and diameter of the balance, are circum- 

 stances very materially connected with the wearing on 

 the cylinder edges. Whatever will prevent this wearing, 

 should be carefully attended to. When the diameter is 

 large, the balance must of consequence be less heavy ; a 

 sort of sluggishness in its motion takes place, the pendu- 

 lum spring making great resistance to the teeth passing 

 the cylinder edges, and causing wearing to go rapidly on. 

 On the contrary, when the diameter is small, and the 

 weight at a proper medium, there is an alertness in the 

 vibration ; the momentum of the balance has such force 

 over the pendulum spring, that it allows the teeth to 

 pass the edges quickly; and hence there is a less tenden- 

 cy to wear them. The diameter of the balance should be 

 less than that in a verge watch of equal size, nor should 

 it be heavier than just not to allow setting, unless where 

 a going in time of winding is used. The cylinder 

 'scapement, on the whole, must be allowed to be a 

 very excellent one; and where care is taken to have it 



3 



made as it ought to be, such watches will give very Escape- 

 good performance. Provision for oil on the cylinder mcnts. 

 should be mn'!e as ample as can be admitted; that is, the """Y"" 1 

 part where the tooth acts, should be as distant from 

 the notch where the wheel bottom passes as possible, 

 and at the same time more distant from the upper cop- 

 per ]>Hig ; the lower notch should not be longer than to 

 give freedom to the wheel bottom to pass easily. 

 When they are made long, which they frequently 

 are, the cylinder will break there if the watch re- 

 ceive a slight shock from falling. The acting part 

 of the tooth, as has already been noticed, should 

 not he too thin, nor the stems too short. If the 

 diameter of the balance is too gi'eat, any addition of 

 motive force will make the watch go slow; if too little, 

 the watch will go fast ; and if, of a proper weight and 

 diameter, any addition of motive force will make no 

 change on the time-keeping. We have made the mo- 

 tive force more than double, and no change took place ; 

 the pendulum spring no doubt had its share in keep- 

 ing up this uniformity. Balances whose diameters 

 we rather small, will have a natural tendency to 

 cross farther, that is, the arcs of vibration will be 

 greater than where the diameters are great. Their 

 weight will be in the ratio of the squares of their dia- 

 meters ; from which it follows, that if the balance is Method of 

 taken away from a watch which has been regulated, estimating 



and another put in its place, having the diameter only precise 

 . . ~ .f - ic i i ' momentum 



one half of the former, before the watch could be re- O f V . M( . 



gulated with the same pendulum spring, the balance lances, 

 would require to be four times heavier than the 

 first. One way of estimating the force of a body 

 in motion, is to multiply the mass by the velocity. 

 Let us then calculate the respective fojces of two 

 balances whose diameters are to one another as two to 

 four. The radii in this case express the velocity. 

 According to this principle, we shall have for the 

 small balance two for the radius, multiplied by eight of 

 the mass, equal to sixteen, and for the great one, four 

 of the radius by two of the mass, equal to eight ; six- 

 teen and eight are then the products of the mass by the 

 velocities ; consequently they express the force from 

 the centre of percussion of each balance ; and as it is 

 double in the small one, it is evident that the arcs of 

 vibration will be greater, having the faculty of over- 

 coming easily any resistance opposed to it by the pen- 

 dulum spring, without requiring any additional mo- 

 tive force. 



Let us take an example done in another way, which 

 is the square of the product of the diameter multiplied 

 by the velocity or number of degrees in the vibration, 

 and this again multiplied by the mass or weight, so as 

 to compare the relative momentum of two balances of 

 different diameters, &c. Suppose one balance to be 

 .8 of an inch in diameter, the degrees of vibration 

 240, and the weight eight grains ; the other .7 of an 

 inch in diameter, the arc of vibration 280, and the 

 weight 10 grains. 



240 X. 8=192X192=36764X8=2941 12. 

 2SO x- 7= 196 x 196=38416 x 10=38*160. 



The balance having the smaller diameter, has its mo- 

 mentum to that of the greater, as 381 is to 29*. When 

 the arcs of vibration are great, the nearer to isochron- 

 ism will the long and short ones be. 



When a little ex pence in the cylinder or horizontal 

 'scapement is not grudged, a ruby cylinder is certain- 

 ly a great acquisition to prevent wearing on the edges; 

 if it is not steel cased, and wholly of stone, it is so 

 much the better, giving a little more scope to extend 



