Proportion Compafs. ggi 
curve, in order to the giving it the requifite form uni- 
formly to operate the degrees of rife upon the teeth of 
the pinion, which comes very nearly to the geometrical 
curve, the operations of which are not to be underftood 
by all watch-makers as this inftrument may be. 
§ 57. Every body fees that the curve of a wheel of 
120 teeth muft naturally be one half fhorter than that 
of one of 60, fince it goes only through three degrees 
whilft the tooth of the pinion goes through 60. The fame 
holds in every cafe in which the curve of the tooth muft 
be figured, according to the degrees it goes over in its 
axis, to operate upon the wheel of any pinion whatever 
that arc of the rife the moft uniformly poflible, and in 
order to join thefe advantages to others ftill more confi- 
derable, it will be ufeful to make ufe of wheels and pi- 
nions 
operer avec uniformite les degres de levees fur 1’aile du pignon, ce qul revient a 
peu de chofe pres a ]a courbe geometrique dont les operations ne font pas de la 
competence de tous les horlogers comme le feroitcet inftrument. 
§ 57. Onfent bien que la courbe d’une roue de 120 dents doit etre naturelle- 
ment plus courte de la moitie que celle de 60 puis qu’elle ne parcourt que 3 0 
pendant que 1’aile du pignon en parcourt 60, &c. 11 en eft de memes dans tous 
les cas ou la courbe de la dent doit etre figuree felon les degres qu’elle parcourt 
fur fon axe pour operer fur Paile d’un pignon quelconque, Fare de levee le plus 
uniformement poflible; etpour reunir ces derniers avantages a d’autres plus con» 
fiderables encore^ il convient de faire ufage-des pignons et roues auffi. nombreufes 
que ' 
