Proportion Compafs . 965 
§ 18. The confideration of thefe difficulties has 
red teed ae hitherto to keep filence upon the general 
con ftru lion of thefe inftruments; inftruments, in my 
opinion, absolutely neceflary for the conftructing of 
movements, fets of wheels, and motions, either rough or 
finifhed, according to the juft proportions. 
§ 19,, But I make bold to let down, as a fundamental 
proportion, that the true fize or relation between a wheel 
and its pinion is absolutely fixed ; and in no cafe whatfo- 
ever arbitrary, as thofe who are not watch-makers might 
pretend : for all the reafons which can be affigned in fa- 
vour of this arbitrarinefs would be as vague and deftitute 
of foundation as if one was to confider arbitrarily the 
true gradation of a fteel-yard relatively to its weight, or 
the length of a pendulum which Swings Seconds, whereas 
the 
§ 18 La confideration de ces difficulties nous a reduits jufques a prefent a 
garder le filence fur la conftrudtion generale des ces machines devenues felon 
nous indifpeniables pour diriger et comftruire des mouvemens, rouages et ca* 
diadtures bruts ou finis felon les vraies proportions requifes. 
19. N T ous ofons done etablir pour principe fondamental^ que lajufte groffeur 
foit le parfait rapport entre une roue et fon pignon eft inconteflablement fixe, 
abfolu, et non arbitraire dans aucun cas, ainfi que tous autres que des horlogers 
pourroient lepretendre; car toutes les raifons que l’on pourroient alleguer en 
faveur de cet arbitraire, feroient auffi v agues et deftituees de fondement que fi 
l’on envifageoit arbitrairement .lajuile graduation d’une Romaine foit Levrot rela- 
te vement a fon poid 3 ainfi que la longueur du pendul a feconde, tandis que ce. 
dernier; 
