of measuring Time at Sea. 43 
ave shall presently find, that of all bodies in motion, there 
are only the latter which can, with any exactness, measure 
time at sea. 
It appears, first, that all bodies, whether fluid or solid, 
moving by the effect of their gravity, are by that alone in- 
admissible in the present case. Besides that, their motion 
will be always more or less accelerated or retarded by the 
shocks that they will receive from the ship; we know also 
that their gravity is variable under different parallels : it is 
therefore not probable that we can ever correct this source 
of inequalities. 
I know of no other person, except Sully*, who in his 
marine or lever clock has pretended to have obviated them 
on this principle, that by adding, proportionally, weight to 
the balance and to the lever, the rate of the clock would not 
be changed; but the academy, in approving the efforts of 
this artist, declares in its report that 7¢ does not adopt all 
his reasonings. Nothing can be more deceitful in effect than 
that on which he founded this pretended property of his 
clock. 
To convince ourselves, let us remark, that the vibrations 
of his regulator, like those of a pendulum, are produced by 
the force of inertia combined with that of gravity; that the 
first cause operates principally on the balance, whose gra- 
vity bas no influence on the time of vibration; that the se- 
cond resides in the lever, whose inertia has very little effect, 
because it descends almost vertically ; and that, lastly, the 
time employed in each vibration depends on the proportion 
which exists between the balance and the lever, that is to 
say, the same as in the pendulum, the ratio of inertia to 
that of gravity. 
The experiment which Sully + made before the academy 
proves nothing. When by adding matter to his balance he 
augments its gravity, he makes also the force of inertia to 
increase in the same proportion; but under the pole, its 
* See the machines approved by the Academy of Sciences, and the author's 
Abridged Description. : 
+ Abridged Description, p.7. 1n this experiment Sully attempts to prove 
that the unequal gravity of bodies in different latitudes produces no change 
jn the going of his machine —T. S. E. 
gravity 
