62 Le Roy’s Memoir on ihe best Method 
high strain of its main spring a second and a quarter in six 
hours more than in the low strain of this spring, where the 
arcs of vibration are reduced to about a quarter of what they 
are when the watch has just been wound up. 
T shall add to what precedes, that I am certain, froma 
number of trials, and it is easy to verify, that, the long and 
short arcs of vibration once rendered isochronous by this 
method, all the intermediate arcs are rendered so also, with 
the greatest exactness: this is what I do not believe can 
easily be produced by compensation curbs, cycloidal cheeks, 
and other methods, by which they have hitherto attempted 
to render the vibrations of the spiral spring isochronous ; 
and when, by dint of penetration and care, an artist has per- 
fected such curbs, &c., can others* expect to succeed equally 
as well? The Academy, without doubt, want a machine 
whose success does not depend on such rare execution. It 
was probably some case of this kind which made a learned 
man say, that the novelties produced by artists rarely have 
their success confirmed by time, it being frequently owing 
to the particular attention which they pay to the execution 
of the pieces which they. announce as their invention ; in- 
stead of which, scientific men seta higher value on things 
more theoretic and less dependant on practice. 
Article IV. 
Where we again establish the necessity of giving to the vi- 
trations of the regulator the greatest possible freedom. 
I believe I have already proved (Article I. Part If.) that 
to give toa clock the greatest degree of accuracy which it 
is susceptible of, it is necessary that the vibrations of its 
regulator should have the most perfect isochronism and the 
greatest freedom possible. 
And now that I am going to treat of the escapement, 
_ (whose disposition must always’ be relative to nature, and to 
~ the properties of the regulator which is used,) to leave no 
%* See Graham’s Letter to Sully, in the Deseviption Abregéc, p. 75. Bor 
deaux, 1726. This work of Sully’s is extremely rare even in France: Berthoud 
was many years before he could procure a copy of it. See note C, page xv, 
of his Introduction to the Traité des Horloges Maitacs.—T. & E. oe 
obscurity 
ee oe 
