2 ' MR. REID ON TIME-KEEPING MACHINES. 



bring the ball again quite up to the place where it fet out from 

 when ihe heal was firft applied, and this with a ball of a 

 moderate weight ; no doubt the weight of the ball may bii 

 made fubfervient to any fize of wires, 

 Mr. Troughton Whether Mr. Troughton has attended to thefe circumflance?, 

 atteTdcito''''' ^ '^"^'^ "°^' ^"^ (ix^p^^a from his propofing, yet, to make 

 thii. fome fort of pyrometrical apparatus for the further proving 



of his pendulums, that the complete compenfalion has not 

 been fully afcertained, only in fo far as regards the calcula- 

 tion of the relative expanfions of brafs and fteel. 



The improvement of clocks, and time-keeping machines of 

 every defcriplion, more particularly ihofe deftined for aftrono- 

 mical purpofes, is a fubjedl that has not a little engaged my 

 time and attention. 

 The pendulum There is a pendulum, having a wooden rod, the conftruc- 

 **^ ^^!«^'" "d^*^ tion of which is defcribed with great neatnefs, perfpicuity, 

 examined. and mechanical knowledge, by its author, (Mr. Ludlam, late 



an eminent profelTor at Cambridge) in his etfays, and recom- 

 mended by him, uho was no mean judge, as one of the beft ia 

 almoft every refped, particularly in fo far as regards the im- 

 puHe from the clock taking place through the middle line or 

 centre of the rod, to be thence communicated in the fame 

 line to that of the ball, that hence no circumgyratory motion 

 fliould take place. Now, although the principle fet out with 

 here, feems completely adapted to prevent this fort of motion, 

 it will be found on trial, as I did, that of all pendulums yet 

 made, it is the moft liable to generate this very fort of motion. 

 it IS liable to a The ball being the middle fruftum of a g'obe, a form whofe 

 thtblfl'mund"^'^^^^^^ is much fpread out from the cenlre to the edge, and 

 the rod as an having a large hole, for the rod to pafs through; this isk'm^ 

 "'*• away much of the matter from the centre, tends much more 



than the lenticular form, to produce the motion Mr. Ludlam 

 The fere w8 wiflied to avoid. Another great fault of this pendulum, is, 

 which are aftcd jj^^j- ^f putting in fcfcws through the wooden rod, to clip the 



•n bv the crutch ^ ri ,i -i e .ir 



do not preserve ^3^ P^""*- ^'^^"^ *"® crutch ; now m changes or weather troni 

 a coniiant dif- inoift to dry, or by heat ami cold, thefe fcrews will accordingly 

 ^""* be found, fometimes to pinch the flat part of the crutch, and 



at other times, to leave it at liberty, or even to allow it to 

 have a conliderable degree of fliake between the fcrew points: 

 hence will arife very diflferent degrees of impulfe communicat- 

 ed to the pendulum ball. Wood has r. \Qiy fenfible la- 



tiludinary 



