kR. REID ON TIME-KEEPING MACHINES. ^ 



tituditiary alteration, by the effeds of heat and cold, or by beciufe ^*ood 

 dry and moid, yet thefe effefls on its length are^ rather but g^3j'Jj'j^^y^''j''g^^_ * 

 very imperceptible, or at leaft, are, in (o ("mall a degree, as perature and 

 have not been well afcertained, to what extent they are; even "^o^^""^^* *<=♦ 

 by thole who have made experiments with it on the pyrometer* 



Mr. Bertiioud condemns wood as being unfit for pendulum The end expati* 

 rods, and although he, and others have given tables of ^^e ^^°J^^^j^^«^d^^ 

 expanfion of various materials, yet none of them have con- 

 defcended to fay, what were the efFc6ls of heat and cold on 

 wood of any fort* 



I am well convinced, that a pendulum may be fo fitted upwooden pen* 

 with a wooden rod, as to perform with fuch a degree of cor- tlulums feem 

 re<5lnefs, that it would be a very difficult matter to fay, whether ^^J^^J°^^^j ^^^^ 

 it, or the beft compenfation pendulum yet conftruded, dulums, 

 when both comparatively^ tried, was the neareft to accurate 

 meafuring of time. 



There has been one circumflance attending all thofe pen- tut ^re often 1| 

 dulums fitted up with a wooden rod, that their errors have conftrufted, 

 been imputed to the rorl, when in fad, they ought to have 

 been imputed to that of the ball, and thefe errors have arifen 

 from the manner by which the ball is hung on the rod, refiing 

 on its lower edge on the regulating nut ; and lead having a 

 confiderable degree of expanfion, clocks having fuch pen* 

 dulums have been found, by thofe who attended properly to 

 their going, to have gone conftanily fader in fummer than in 

 winter. Let the ball therefore be hung by its centre on the 

 rod, and a much greater degree of accuracy in time-keeping 

 will be feen to follow. 



In confequence of my trials with Mr. Ludlam*s P^i^^i^^un^s, j^^^^^^g^ j^^ 

 they were found to be extremely troublefome to put on beat, dulum. 

 from their firong tendency to this gyratory fort of motion, it 

 being fome while, before they would come to move fteadily ; 

 I hit not only on a method of putting a clock, as it were me- 

 chanically on beat, (the common way being by the ear) but was 

 led to think on a way of conftrufting a pendulum, in which 

 (his gyratory motion could hardly take place, even although 

 the pendulum fliould be but indifferently fitted up. This laft 

 was by following a method quite the reverfe to that of Mr* 

 liudlam's, in making the pendulum ball, which I made in tha 

 ufual or lenticular form, and in order that it fiiould have as 

 much of its matter preferved at the centre, there were two 



B 2 iteel 



