In the marine keepers which Mr Mudge himself had made, the 'scapement is on a very flattering principle, which he suggested as the means of improvement many years before he put it in practice. Its good performance seems to have been unequalled ; and it is singular, that, notwithstanding the efforts of three or four of the best hands that could be got to the establishment set up by Mr Mudge, junior, in order to put these 'scapements to time keepers which they were employed to make, not one was ever produced that was at all equal to the original ones. The 'scapement is apparently very complex, elaborate, and of course expensive in making ; yet, when once executed, it will be permanent in its effects, and require no after ad justment like the common detached one. After what has happened, it is not likely that it will be again adopted. The basis of it is that of the curious old crown wheel and verge. In place of the verge being in one, having two pivots and the balance rivetted on it, let us conceive that each of the pallets of the verge has an arbor and two pivots, and that the balance is on a double kneed crank, having a pivot at the end of each knee, one being near to the foot, the other near to the collet on which the balance is rivetted ; these pivots, and those of the pallet arbors, are in one upright line, coinciding and concentric with one another, having their motion, as it were, free and independent of each other, unless when in a part of the action of the 'scapement ; the face of the pallets, in place of being flat, are hollow, or a little curved, having a nib at the edge to lock the wheel by. On the lower end of the lower pallet arbor is an arm pro jecting nearly as far. as the bending of the crank knee, in n n n which is fixed a pin that acts on the inner side, and near to the end of the arm, and is alternately acted upon ; close by the arm, and on the pallet arbor, the inner end of a spiral spring is fixed ; the outer end is in a stud, having a certain tension or bending up before fixing in the stud. The up per pallet arbor has the same as has been described to the lower one, and a pin in the upper knee of the crank. It may easily be conceived, that the length of the crank knees ought to be such as to allow it to sweep round and behind the crown wheel, its boundary or banking being that of the crown wheel arbor, or its pinion arbor. When the pallets are not raised up, and the wheel unlocked, the tendency of the spiral springs is to bring them down within the spaces of the crown wheel teeth. Suppose the upper pallet rais ed up, and the wheel locked, the under one being in the re vers,. position, and the balance vibrating towards the right, the pin in the upper crank will, of course, meet with the small arm, and carrying it on a little way, the w heel-tooth gets disengaged, by which the wheel getting forward, the lower pallet is raised up, and the wheel is again locked. In
the interim, the tipper arm being carried on a few de grees, by means of the momentum of the balance in vibrat ing, hends up the spiral still more than what was done by the wheel raising up the pallet, the re-action of which, in the returning vibration, gives impulse by means of the arm on the pin of the crank. The pin in the lower crank now getting forward, meets with the arm of the lower pallet arbor, carries it on, the wheel gets disengaged, and so on. This 'scapement cannot set itself off; for before this can be effected, the balance must get some degree of external cir cular motion in its plane. The balance may be said to be free in that part of the vibration, after the pin of one crank has left its corresponding arm, till the pin of the other meets with its arm ; this is, however, very momentary. The balance had on its arbor two spirals or pendulum springs, for the purpose of obtaining the most isochronous vibrations. Something in this way had been proposed by one of the Bernoullis. Drawings and a description of this 'scapement will be found in the work published in 1799, by Mr Thomas Mudge, junior. The compensation, like every thing of Mudge's, is ingenious, though nothing of this kind can ever be equal to that of being in the balance itself. The train of wheels went contrary to the ordi nary direction, and we have no satisfactory reason assigned for it.
Although the balance in pocket watches may be put very well in equilibrium, yet many things contribute to make them go unequally in different positions, such as in hanging, laying, &c. which require time, and give a great deal of trouble, before they can be completely corrected. In order to get the better of this, Breguet, an eminent watchmaker in Paris, contrived a 'scapement, which, with the pendulum spring stud, revolved round the centre of the balance once every minute. By this means, whether the balance was in equilibrium or not, the going of the watch was little affected by it, as every part of it was up and down in the course of a minute, which compensated any want of equilibrium. This connivance is merely mentioned by Ber thoud in his Histoire, as he did not think himself at liberty to give any description of it, since Breguet had a patent or brevet d'invention to make them. We have heard it said that the same invention had been made before by the late Mr John Arnold.
Those who wish for farther information respecting 'scape ments, may consult Traite d' Horlogerie par M. Thiout, Histoire de la Mesure du Temps, par M. F. Berthoud, and the Transactions of the Society for the Encouragement of Arts, Commerce, &c.
On Compensation Balances.