972 Mr. le cerf on a new-invented 
number upon a pinion of fix, muft operate in a mutual 
proportion the 6o° of rife by which the angle of the 
pinion is open; from whence it happens, that the angles 
of the v/heel, open only at 5 0 , will raife only 6o° above 
thole of the pinion ; but, if they are open at 7°, the rife 
will be of 70° inftead of 6o°- 
§ 30. There are like wife a great number of defeats 
which are increaled two and three-fold by the ufual con- 
fequences attending wheel-engines, the fmall tooth of 
which is conftantly expofed to become fhorter than the 
large ones, in proportion of its fize. This happens in 
the following manner; the file, which is to round off, 
working on each fide equally, does not take more from 
the fide of the large tooth than it does from the fmall; 
confequentlv, the fmall one is fharp whillt the large one 
ftill 
que chaque angle de la roue n’importe dequel nombre fur pignon de fix doit ope- 
rer en mutuelle proportion les 6o° de levees dont Tangle du pignon eft ouvert; 
d’ou fuit que les angles de la roue feulement ouverts a 5 0 , n’operermt que 50° 
fur ceux du pignon, mais que s’ils font ouverts a 7 0 la levee fera de 70° au lieu 
de 6o°. 
§ 3°. Je ne parlerai pas d’un concours de vices qui fe double et fe triple 
par Peftet ordinaire des outils aux dentures on la petite dent eft expofee a deve- 
nir toujours plus courte que les grofles, en railbn de fa petitcfle; cela arrive de 
cette maniere, la lime a arrondir mordant des deux cotes egalement; rTemporte 
par plus d’etoffe du cote de la grofie que de la petite dent, par consequent il y a 
encore du plat fur la groffe que la petite eft deja pointue, il fauc neeelTairement 
4 raecourcir 
