CLOCK. 



effect tliis, a catch, or locking piece, re- 

 strains all the motion of the swing 1 wheel, 

 till the instant when the pallet is to be 

 impelled by it, when it raises the catch, 

 sets the wheel free, and is driven for- 

 ward by its impulse ; immediately after 

 which, the catch again falls into its place. 

 A great variety of escapements have 

 been contrived on this principle by vari- 

 ous ingenious men : those in which springs 

 are usedin the locking pieces instead of 

 pivots, invented by Arnold, seem now 

 most preferred. 



The detached escapement was applied 

 first to chronometers, or time-pieces, but 

 is now used for astronomical clocks. 

 From the best accounts, Julien Le Roy 

 invented the first about 1748 ; since that 

 time, Grignon, Mudge, Cummins, Nichol- 

 son, and Arnold, have contrived various 

 escapements of this kind in England; and 

 Peter Le Hoy, Sully., Du Tertre, De Be- 

 thune, Le Paute, Arnaut, Robin, Ber- 

 thoud, &c. on the continent. See CURO- 



NOMETKtt. 



In the year 1715, Mr. George Graham, 

 before mentioned, made a most material 

 improvement in pendulums, by affixing 

 an apparatus which tended to raise the 

 centre of gravity of the whole, as much as 

 the lengthening of the rod by heat tended 

 to depress it: this he performed by sub- 

 stituting a glass cylinder, containing mer- 

 cury, for the pendulum ball. He after- 

 wards suggested the idea of using the 

 opposite expansions of different metals, 

 as a compensation for the effects of vari- 

 ation of temperature of the air in pendu- 

 lums, which was directly afterwards 

 adopted by Harrison, at that time an ob- 

 scure carpenter in the village of Barton, 

 Lincolnshire, who surprised the world 

 with the invention of the gridiron pendu- 

 lum on this principle. 



In Harrison's pendulum five bars of 

 steel and four of brass were so arranged, 

 that they produced two expansions of 

 brass upwards, and three of steel down- 

 wards, so proportioned to each other, 

 that the ascending expansions fully com- 

 pensated those in the contrary direction. 

 This pendulum has been since its inven- 

 tion generally used, where very accurate 

 measurement of time was necessary. A 

 further description of it, of Elliot's pen- 

 dulum, (which was the next made on this 

 plan, and differs little from it,) and of the 

 others here mentioned, will be inserted 

 under the article PEXUULUM. 



It has been supposed by several, that 

 the tubular pendulum (which is also a 

 modification of Harrison's compensation) 



is but a very recent invention : but the 

 writer of this article having met with one 

 by accident, which was made upwards of 

 thirty years ago, thinks it but justice, 

 both to the public, and the ingenious ar- 

 tist who directed its construction, to op- 

 pose this opinion. This pendulum is in 

 possession of Mr. Patoureaux, watch and 

 clock-maker. 15, Wardour-street. It was 

 made by Mr. William Brown, a clock- 

 maker well known to the trade, who has 

 been dead upwards of five years, and 

 who formerly resided nearthe Seven Di- 

 als. His brother, ajeweller, residing in 

 15, Coventry Court, Hay-market, was his 

 executor, and sold the pendulum to Mr. 

 Barrett, clock-maker, of Compton-street, 

 some years ago, from whence Mr. Pa- 

 toureaux bought it. Mr. Brown, the jew- 

 eller, informed the writer that this pen- 

 dulum had been made by his brother up- 

 wards of thirty ^years ago, just after he 

 had served his time to Mr. Chandler, then 

 of King-street, Seven Dials, (whom he 

 afterwards succeeded in his business;) 

 and that it was made by direction of Mr. 

 Chandler, who, as far as he knew, was 

 the inventor of it : and in corroboration 

 of this assertion, Mr. Hampson, working 

 clock-maker, 22, Greek-street, Soho, 

 declares, that he made several pendulums 

 of the same construction for Mr. Brown, 

 upwards of seven years ago. This tubu- 

 lar pendulum, which at present we must 

 attribute to the ingenuity of Mr. Chand- 

 ler, is composed of two tubes and a 

 rod of iron, and two tubes of brass. The 

 iron rod is about a quarter of an inch in 

 diameter, and is suspended by a spring 

 in the common manner ; it is inclosed by 

 the first brass tube, to which it is con- 

 nected at bottom : an iron tube, sup- 

 ported by the top of the brass tube, then 

 descends a little below it, and supports 

 by its lower extremity the second brass 

 tube, which rises a little above the for- 

 mer tubes, and from the top of it the se- 

 cond iron tube descends below all about 

 two inches, into the substance of the 

 pendulum bob, which is very large and 

 heavy: the bottom of this last tube con- 

 tains a nut, into which a screw (having* 

 a milled head beneath that sustains the 

 bob) passes from below, and raises or 

 lowers the bob, as required for the ad- 

 justment . of the rate * of going of the 

 clock. We may date the invention of 

 the tubular pendulum, from the fore- 

 going information, about the year 1775, 

 though it may yet be found to be of 

 a still earlier period. The foreman of 

 Mr. Villaumy, clock-maker to the Prince 



