Invention for oitaintng a Standard Meafure, 31 



^ears, was at length produdive of competition on the part of five candidates, one of whom, 

 Mr, John Hatton, watchmaker, of London, propofcd in March, 1779, to obtain a meafure by 

 applying a moveable po;nt of fufpenfion to one and the fame pendulum, in order to afcertaiii 

 the difference of length between two portions fucceflively made to vibrate, and meafure dif- 

 ferent known parts of time. This attempt, whether from its imperfeiSion in principle, or 

 the difficulties found by its author in carrying it into efFecSt, was not confidered by the Society 

 as intitled to their reward ; but as an encouragement for the farther profecution of the fubjeft, 

 they prefented the inventor with thirty guineas. After this time, the purfuit remained unattended 

 to for fome years, till Mr. Hatton's plan was taken up by the late John Whitehurft, F.R.S. an 

 ingenious mechanic and worthy man, but poflelfed of very little fcience, at whofe houfe I faw 

 the machine going in the year 1786, which he afterwards defcribed in a pamphlet on that 

 exprefs objeft*. He was, at that time, of opinion, that his pendulum, which confifted of a 

 ball of lead fufpended by the fine flatted fteel wire, called pendulum wire (of which the length 

 was determined by an adjuftable clip), would g-ve a meafure by the difference of its leno-ths, 

 as before explained, which would not beaffeftcd by the ditnenfions of the weight itfelf; and his 

 weight was accordingly a very rude-faftiioned round piece of metal. It was not without fome 

 difficulty that I perfuaded him to the contrary, whicn is a point concerning which men of in- 

 formation carmot have two opinions; but afterwards, when he became convinced, he propofed 

 that the ball fliould be made of a diameter anfwering to fome aliquot part of the meafure 

 expedled to be obtained, or deduced from crude experiments, and afterwards correfted from 

 tile a£lual refult ; v.'hich corrected baii, being ufed to obtain a fecond refult, fliould be again, 

 corrected, and this process of apjjroximation continued till the refuks were not found to differ 

 by any perceptible quanti'ty. I have reafon 10 believe, however, that he never ufed this 

 method, nor even took the trouble to give -any precifioa of figure to his ball, with which he 

 made the experiments recorded in his pamphlet. 



After the death of Mr. Whitehurft, his apparatus came, by purchafe, into the hands of Dr. 

 George Fordyce, F.R.S. who coniiderably improved it, and gave a defcription of the fame to 

 the royal focietyf. The moft important improvement confifted in a contrivance to prevent 

 the effedl of variations of temperature upon the pendulum, which the reader will perceive to 

 be highly valuable for the mechanical /kill difi^layed in the execution, and in principle fome- 

 \rtiat refemWing the fixed appararas deicribed at page 6( of our firft volume. As the fimili^ 

 tude of the two apparatus of Whitehurft and Fordyce muft render many particulars of the 

 defcriptbn. of the fame in both, I have givea no copy of the drawings of the former; but ihall 

 fpeak of both conjundlively. 



Fig- 3v Plate II, will afford a more perfeft notion of the apparatus than may, perhaps, have 

 leea conveyed by the verbal defcriptions already given. O reprefents the pendulous ball fuf- 



* An attempt towards obtaining invariable meafiires of length, capacity, and weight, from the menfuration 

 of time, independent of the mechanical operations requifite to afcertain the centre of ofcillation, or the uue- 

 length of pendulums. By John Whitehurft, F.R.S. 4to. 34 pages, with three plates. London, 1787! 



t Jiccount (f ^new pendulum, Phil. Tranf. 1794; from whicliour drawing is copied of a fmaller fize, with 

 fome amendments of the perfpeftive. 



pended 



