3« Apparatus f. r awarding a ' Standard Meafurs ly the ''Pendulum, 



.pcnded from Q.by the fine flat fteel wire O N. In Mr. Whitehurffi's machine, the ball 

 ■weighed 12251 grains, or upwards of two pounds troy, and the wire, which was flat fteel tem- 

 fered, was of fuch a thicknefs, that 80 inches in length' weighed nearly thn^e grains. The piece 

 W I affords a notch through which the wire pafles, and which limits the length of the effe£tivc 

 pendulum. This piece is fixed to the frame-plate of ^ train of wheels, fimilar to that of an 

 eight-day clock, which, by means- of a crutch of communication applied to the pendulum- 

 wire, ferves to maintain the vibration, and keep account of the time; The efcapement is the 

 <lead beat of Graham*, with the addition of an arm fpringing from the axis of the pallets up- 

 wards, and carrying an adjuftable weight; the ufe of which is to fet the pallets themfelves to 

 the fame vibration as the pendulum- is intended to perform: a condition which Mr. White- 

 liurflr, in common with other artifts,-fuppofed to be of value to prevent the maintaining power 

 from influencing the meafure of - time, though this, in faft, depends more particularly on the 

 4lru6ture-and figure of the pallets f. 



The principal fupport to which Mr. Whitehurft's apparatus was attached, conftfted J of 

 two planks of deal, two- inches thick, nine inches wide, and nearly fix feet long, which bsing 

 framed edge-wife together, left a groove to admit certain bolts, or Aiding parts, from the move- 

 ment S S, by the help of which it can be raifed or lowered, or fixed at any deiired elevation. 

 -In the actual experiment, therefore, the movement is to be Aided up and fixed near the top of 

 the frame, and the pendulum then adjufted to the longer vibration by means of the fcrcw A, 

 which'taifes or lowers the cockE G N. This, in Mr. W hitehurft's procefs, was one forty- 

 fccond part of a minute. There is a brafs rule or piece 5 feet 2 inches long, and one quarter 

 of an inch thick, fixed at its lower end in one of the planks in a vertical pofition-to receive and 

 preferve the meafure. ^ On this brafs piece, at the temperature of 60", a fine ftroke was then 

 drawn by means of a proper tool applied againft the edge of the plate of the movement. In 

 ths next place he Aided the movement about five feet lower, and, by means of a fcrew applied to 

 the bottom of the frame-plate, the piece I W was adjufted to the wire till the vibrations be- 

 came 84 in the minute. At this period, another ftroke was drawn as before on the brafs rule, 

 at the fame temperature of 60°, which is fuppofed to have been kept up during the whole of 

 the operation from firft to lafl:. This fuppofition of an equal or fteady temperature of the air 

 in an apartment, can hardly be admitted, except with regard to the mean temperature in a clofe 

 Subterraneous place, which is moft fteadily kept during fummer, becaufe the warmer air from 

 above has then no tendency to defcend. 



-Mr. Whitehurft's machine was fixed in the corner of a firft-floor room, in Bolt-Court, 

 Fleet-ftreet, which, I think, was wainfcotted. The meafure obtained as the diiFerence of the 

 <wo lengths aforefaid, vibrating through femi-arcs of 3° 20', was 59,892 § inches, and the 

 kngth of feconds pendulum for London, thence refulting, proves 39,1196 inches, inftead 



*'Philtf. Journal, II. 51. f Ibid, p. 49, 50. 



" ^ Dr. Fordycc retained this part in his improved machine. Philof. Tranf. 1794, p. 16. 



§ Sir G. Shuckburgh Evelyn, who afterwards meafured it, found it about 0,0015 inches longer at 54', 

 which is nearly equivalent to tlie expanfion of brafs from 60° to 64°. See Philof. Journal I. 58, an-d Phil. 

 Tranr. 1798, p. 135. 



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