Proportion Compafs. 953 
rious, and fb imperfect, that it is they which have pro- 
bably given rife to a general relaxation with regard to 
the true principles, and to the adoption of rules and mea- 
fures arbitrary, vague, and which produce very confidera- 
ble errors: fuch, for inftance, is the error of taking a 
little more than three points of a tooth in order to de- 
termine the fize of the pinions of fix, without regard to 
the revolutions which the different numbers of the teeth 
of the wheels produce. The confequence is, that an 
equal meafure being taken upon a wheel of 18 and 
upon one of 7 2 teeth produces a variation of one entire, 
revolution, as will be fliewn hereafter. 
§ 4. For inftance, the pinion is the divifor of the 
wheel as well as that of the circle, each tooth of which 
is to raife its required proportion of degi'ees. A pinion 
of fix is to raife 60 0 per tooth becaufe 6 x 60 = 360 ; one 
of 
des moyens aufli longs que penibles et imparfaits, et qui vraifemblablement ont 
donne lieu a un relachement general fur les vrais principes, en fuivant des regies 
ou mefures aufli vague-s qu’arbitraireset qui menent a des -erreurs tres confidera- 
bles; teiles font celles de prendre un peu plus que trois pointes de dent pour 
determiner la groffeur des pignons de fix fans diftinAion des revolutions que pro- 
duifent les differens nombres de dents des roues. Par confequent la meme mefure 
prife fur une roue de 18 comme fur celle de 72 dents, produit une ecart 
d’une revolution entiere, ainfi que Pon Pexpliquera ci apres. 
§ 4. Par exemple, le pignon eft le divifeur de la roue aufli bien que celui du 
cercle, dont chaque aile doit lfever fa portion de degres requife ; un pignon de 
•Vol. LXVIII. 6 C . ^ doit 
