Apparatus for preventing the EffeEls of Heat and Cold on Pendulums. 65 



but If the gain be produced by cold, the fpring predominates, and the weights will accord- 

 ingly require to be fet farther out. 



I have not met with any application of this principle to pendulums, though it may be 

 ■applied to them in a variety of methods. Fig. 3 reprefents an apparatus by which I have 

 fufpended the fimple pendulum of a clock in my poirelTion. Its chief advantage con.lfts in 

 the facility ofadjufling for temperature and rate, independently of each other, without 

 flopping the clock. It is peculiarly applicable to the pendulum for obtaining an univerfal 

 meafure, contrived by Hatton and improved by Whitehurft and by Dr. George Fordyce *. 



In the Figures 3, 4, 5, 6, 7, 8, 9, Plate V, the fame letters denote the fame things. 

 Fig. 3 exhibits the entire apparatus together, and the other figures fliew the parts fepa-v 

 rately taken. II is a brafs platform, which is to be firmly fcrewed in the horizontal po- 

 Ction upon the fleady fupport intended to fuftain the pendulum. At OO are tv.o flits 

 tlirough which a pair of fprings pafs, and ferve in the ufual manner to afford the centres 

 of fufpenCon of the pendulum. Between two edge bars KK is included the tapped part 

 of a piece of turned fteel FF, of which nearly one half L is tapped with a left hand fcrew, 

 and the other half R with a right-hand fcrew of the fame thread, a fmall portion near the 

 middle being reduced to afford a complete termination to the fcrews. The outer tails at the 

 extremities FF are fquared to receive a milled head G for the purpofe of moving it round. 

 Two bridge-pieces HH are tapped to ferve as nuts to the fcrews, and are fo carefully filed at 

 bottom, together with the edge bars, that when the bars are fixed to the platform the bridge- 

 pieces move ftiffly along the face when the fcrew is turned. The motion, from the nature 

 of the fcrews, is in each equal, and contrary to the other. At the outer corner above of 

 each bridge-piece an edge is prominent, which is reduced at top, all but the corners, to 

 afford a fleady lodgement for a compound bar EE, without fuffering it to touch the reft of 

 the furface of thofe pieces, or to move at all horizontally. The bar EE is compofed of 

 brafs and fteel, the brafs being laid uppermoft. It is perforated in the middle at (^Fig. 8, 

 and properly opened, to afford a Heady bearing for the lower extremity of the fcrew AB, 

 Fig. 3, of which the figure may be feen at S, in Figure 7. The fcrew is provided with 

 a double milled head, and graduated circle, each divifion of which anfwers to a difference of ' 

 one fecond in the daily rate. The branches MM fupport a face, bearing either a nonius, or, as 

 I have It, a fingle ftroke, for the purpofe of fetting the fcrew AB. The nut C receives the 

 fprings of the pendulum In a flit P, terminating above In grooves VV, Fig. 7 ; and the 

 extremities of the legs TT are fufficiently below S to allow the weight of the pen- 

 dulum Itfelf to preferve the vertical fituation of the fcrew. From the nut C proceeds a 

 flat plate DD, which fills the whole fpace between the edge bars KK, and prevents the nut 

 from moving horizontally, while It is left at liberty to rife or fall in the vertical direclion. 



The effecl of this apparatus will be underflood without difficulty after this defcription. 



' I do not pretend to infinuate that the praftical folntlon of this prohlem has yet been cleared of the many 

 difficulties which attend it. The pendulum here mentioned conlifls of a flat fleel wire fufpending a weight, 

 which vibrates from a notch in a plate adjuftablc at diflfcrent licights to mcalure tlie linear diiFcrencc bc- 

 tuttn the fcconds and half-feconds pcndulom. Mr. Hatton, as I am infarmcd, applied many ye:irs ago to the 

 Society for the Encouragement of Aits for a premium in favour of thii invcntiun. Mr. Whitchurft purfucd 

 the fame objefl after\vard5 ; and at his death the apparatus was purchafcd by Dr. George Fordyce, who haj 

 given an account of it, with drawings, in the Philofopliical TranfaiUons for the year 1794, l^S' *• 



. Vol. I— Mat 1797. K When 



