of measuring Time at Sea. 47 
where it was before; this index does not ascend to the same 
point, but rests below. 
These experiments appear to show that the vibrations of 
the spiral spring can measure time but imperfectly : but here 
follow several ‘considerations that must convince us of the 
contfary. 1st, In the vibrations of this spring, its contfac- 
tion and opening are only momentaneous: adly, By sup- 
posing that in its contraction, for example, it had been bent 
a little, it would return presently to its proper opening. But 
even when it experiences some loss on one side, this cannot 
be done without its gaining it on the other, as daily expe- 
rience proves; There would result, therefore, from this a — 
compensation. All the inconvenience that would follow is, 
that the watch will not be so perfcetly adjusted in its escape- 
went. Lastly, the experience of watches with dead escape 
ments * confirms again what I have advanced. The greater 
part, after having gone for several years, are still found to 
be regulated when they have been cleaned, if there has been 
no considerable wear in the parts of their escapement. 
These observations show, nevertheless, that we cannot 
take too much pains for the spiral spring to be fastened in 
a natural and unconstrained situation f (as recommended by 
Daniel Bernoulli). This is what does not take place in most 
watches, and it is (as we shall see in the end) that which I , 
have particularly endeavoured to execute. 
We must conclude also from what precedes, that nothing 
would be more disadvantageous in watches than two spiral 
springs in contraction, as John Bernoulli has proposed f : 
for then the effects observed by our eluterometer would ab- 
solutely take place. 
Besides, a very simple reasoning suffices to convince us. 
that there is not in nature any spring which is not in the 
case of the constrained equilibrium (l’equilibre forcé) recom- 
mended by M. Bernoulli f. 
* Echappements a repos. See Berthoud, Traité des Hor. Marines, p. 316. 
§ 969; and Essai sur? Hor., tom. ii. 1642.—T. S. E. 
4 Recherches Méchaniques et Astronomiques, p. 45. 
t Recherches Physiques sur la Propagation de la Lumitre: we may consult 
also on this subject D’Alembert’s Opuscules Mathématiques, tom, v. p. 503. 
in the piece which obtained the prize of the Royal Academy of Sciences 
for 
