152 . Le Roy’s Memoir on the best Method 
force; whence we may legitimately infer, that what is’ de+ 
stroyed by friction is almost nothing: now the obstacle 
arising from my detent must“be reputed of no value, con- 
sisting in a mass always the same, whilst the friction varies 
continually. 
E made the same trial with a seeonds pendulum having 
an enchor escapement. The whole motion of the pen- 
duluny ceased in about thirty minutes, whence I believe I 
can conclude, considering what has been seid of the resist- 
ance of the detent, and of the motion which remains to the 
balance after seven minutes, that this balance im the new 
watch has almost as much regulating power as this pendulum. 
Ihave said that my pallet was situated near the circum- 
ference of tle balance. [ placed it thus,.m order that it 
might be drawn. by a point in its circumference of percus- 
‘sion, which point is where the wheel in its action makes no 
effort on the pivots, and where the balance only receives the: 
eircular motion*. 
Moreover, although the escapement of the new watch, 
and that whith M. le Roy presented to the Academy in 
1748, are founded on the same principle, they differ never+ 
theless essentially. In the first, the effect of the detent 
operates by means of a small spring, which brings it back. 
into the teeth of the wheel: in this there is nothing of that 
kind, as we have seen. Various trials have proved to me the 
inconveniences of the spring escapements. These springs: 
are either strong or weak: in the first case, it is to be feared: 
that the detent would be disengaged by shocks; in the se- 
cond, you:rive to the regulator a considerable obstacle to- 
overcome in each vibration, which obstacle being the same 
for the smallest as it is for the largest arcs, must be disad+ 
‘vantageous. Besides, if this detent, that is meved by so 
feeble a spring, meets with ever so slight a difficulty ; or if this 
spring loses its strength, it does not enter sufficiently quick 
* It is extraordinary that M. le Roy nowhere mentions his having applied 
jewels either to the pivot-holes or to the balance of his watch. Sully (p.248, 
Regle Artif. du Temps) says that in 1704 Sir Isaac Newton showed him a watch, 
that was-put into his hands to try by Messrs. Facio and de Baufre, the pallets 
of whose balance were formed of a diamond; and expressly mentions that the 
art of piercing rubies was invented by this M. Facio, of Geneva, about the 
year 1700. The utility ef their application must therefore have been fully 
- known to watch-makers at the time Le Roy wrote this paper, and it is extra- 
ordinary that he did not make use of this additional advantage. ; 
mie 
es 
