50 Le Roy’s Memoir on the best Method 
know what is to be depended on with regard to the vasa 
of isochronism of the vibrations of the spiral spring con- 
nected with the balance*: nevertheless nothing, perhaps, in 
philosophy is more obscure. 
The following experiment, from which it has been at- 
tempted to pane this isochronism, cannot, in my opinion, 
form a complete proof: 
“< In sonorous bodies, that are struck or played upon with 
more or less force, the tone remains, they say, always the 
same; nevertheless they would heighten or lower seusibly 
if there happens the least change in the duration of their 
vibrations ; the different extent of these vibrations has there- 
fore no influence on the time in which they are made. 
Now,” continue they, “ a balance joined to a spiral spring 
is analogous to the wire of a harpsichord ; when either of 
them vibrates, it is always a mass moved freely by an elastic 
force: therefore they conclude, “ the balance, assisted hy 
the spring, makes its reciprocations more or less wide, in 
times that are perfectly equal.” ; 
This reasoning proves, moreover, that all the vibrations of 
2 springing body are nearly isochronous, the ear not being 
sufficiently delicate to perceive the small differences in the 
tones. Besides, M. de Mondonville has found that the 
tone of a chord rises more or less according to the degree of 
force which presses it, and that this goes as far as a semi- 
tone, when it is done very softly, although the gradation 
observed in swelling and softening the sound commonly ren- 
ders this difference insensible to the ear +. 
Something more precise is therefore necessary to know 
exactly whether (allowing for friction, for the resistance of 
the air, &c., circumstances to which we shall attend further 
on) the vibrations of the spiral spring connected with the 
* John Hautefeuille, an ingenious mechanic, born at Orleans in 1674, ap- 
pears tu have been the first who applied a small steel spring to regulate the 
vibrations of the balance. It was laid before the members of the Academy of 
Sciences in 1694; and when Huygens applied for his patent for this discovery, 
it was opposed, because Hautefeuille had made use of it before him. See his 
Life in Dr. Hutton’s Dictionary —T. 5. E. 
+ M. Ferrein’s Dissertation on the Formation of the Voice, in the Memoires 
of the Academy of Sciences for 17-41. 
7 balance 
