Watch finishers always made the pendulum spring for the watches of their own finishing, while at the same time, knowing nothing of its properties, the general practice was to taper them, so that the coils, when bending or un bending, should preserve an equal distance with one ano ther; and this method has been used ever since the appli cation of the spiral spring. Those who finished watches for Mudge and Dutton, were never employed to make the pendulum spring. This was always done at home by either Mudge or Dutton themsehts, who, no doubt, endeavoured to make them as nearly isochronous as possible. This, among other causes, perhaps gave their watches the cele brity which they at that time had deservedly acquired.
The pallets of the 'scapement at the turret clock in Greenwich Hospital, are said to have been contrived by Mr Smeaton. The following narrative will show how he came to be concerned in it. It may be observed, that at that time he was one of the commissioners.
The turret clock, which is in the cupola of Greenwich Hospital, was undertaken by the late Mr John Holmes, and executed under his directions by Mr Thwaites. But be fore any thing was done, Mr Holmes consulted two gen tlemen, who happened to be his most intimate friends ; the one was the Rev Mr Ludlam of Cambridge, the other Mr John Smeaton, both of whom were very eminently quali fied to give such advice as was wanted in this business, not only about the 'scapement, but how every part of the clock should be fitted up, so as to insure safety and utility in its performance. Several very long and masterly letters (of which Mr Reid has copies, though none of the originals were ever published) passed between them or, that occa sion, and evince much ingenuity. They agreed that the 'seapement should have a recoil. Mr Smeaton recom mended, that the pallets, in place of having planes, as was common for their acting parts, should have curved sur faces, the leading pallet being concave, and the driving one convex ; and when the pendulum was at or near to the extremity of the vibration, the 'scapement should then be nearly dead. This was, as he said, what " old father Hind Icy at York had ultimately come into !" Mr Ludlam ad vised, that the swing wheel teeth should be thick and deep, and of such a shape as to roll as it were on the pallets, and not to slide on them, which would prevent biting or wearing. The pallet arms were of brass, made so as to put it in the power of the clockmaker to take the pallets very easily out, when repairing was necessary. These
methods had long before this been used by Harrison, and were adopted in a clock of his in Trinity College, Cam bridge, as mentioned by Mr Ludlam. Broad rubbing sur faces were strongly advised by them. Mr Smeaton at this period took away gudgeons from a mill wheel, whose di ameters were only 2i inches, and put others in their place of 8 inches, with great success, as it afterwards proved. On the same principles which have just now been mention ed, was the 'scapement made for the clock, which Mr Tho mas Reich put up in St Andrew's Church, Edinburgh ; and although it has been going for about thirty years, there is not yet the smallest appearance of biting or wearing on the pallets.
'Scapements have been divided into classes, one of which has been called those of the remontoir kind. Now, the mechanism of a remontoir may be applied to any 'scape ment, and even then it can hardly be said to form a part of it, more than the wheels of the movement, or the weight which moves them.
The motive force passing through the wheels, may at times be unequally impressed upon the 'scapement either of a clock or watch. This idea gave rise to the invention of what has been called remontoirs ; that is, that the move ment should at intervals be made to wind up either a small weight, or bend up a delicate spring, which alone should give its force to the 'scapement, by which means the pen dulum or balance was supposed to be always impelled by an equal and uniform force. The earliest thing of this sort was used about the year 1600. Huygens applied it to some of his clocks, and gibes a description of it in his Horologium Oscillatorium ; and Harrison had one in the marine time-keeper, which gained hint the great reward. Wc are of opinion, that they are of no great use either to a clock or a spring time-piece ; for if the pendulum of the one is well fixed, and the momentum of the ball is not too little, any small inequalities of the motive force through the wheels will hardly be perceptible ; and in the spring time-keeper, the isochronism of the pendulum or balance spring is sufficient to correct any inequalities whatever in its nfotive force. As their mechanism, however, is curi ous, and has been rarely described, it may not be uninte resting to our readers to have such an account of it as would enable them to make and adopt it should they think it proper.