Aa Le Roy’s Memoir on the lesi Method 
eravity augmenting without its quantity of matter changing, 
iis inertia would not experience any increase. 
In heavy bodies in motion, to compensate the effect of 
their different gravity in various climates, (an effect which 
may go so far as to retard a second pendulum two minutes in 
twenty-four hours, when removed trom the parallel of Paris 
to the equator,) it would be necessary to find an expedient 
by means of which their inertia is proportioned always to 
the increase or alteration of their gravity; but the force of 
inertia of bodies, being a first and unalterable cause, this 
does not appear possible. 
In vain would they pretend to estimate the differences we 
have just spoken of, in keeping a register of the parallels 
under which they would navigate, and of the time which 
they would remain there. Besides all the difficulties of this 
method, and the very complicated calculations which it 
would require, it cannot be exact without a perfect homo- 
geneity in the different parts of the earth, which homoge- 
neity appears to be contradicted by the observations of the 
different lengths of the second pendulum made in different 
climates: it supposes, moreover, that the sailor can know, 
several times each day, at what height he 1s; which is a very 
strained supposition. 
A long detail on this subject would be-useless. We know 
sufnciently the defects of clepsydras and sand-glasses: we 
are not ignorant of the inconveniences of the sinmuland tri- 
angular pendalums, &c. proposed by M. Huygens; or of 
those coupled together by wheels acting in cach other, hike. 
those tricd by the late M. Dutertre*. Experience has suf- 
ficiently shown the defects of these methods and of many 
others, which for this reason I shall pass by in silence. 
I come now to bodies which make vibrations by their in- 
ertia, combined with that universal force which directs the 
needle of a compass. 
The celebrated Dr. Hook + havete that we might es 
it advantageously to a clock in the quality of a regulator. 
But Graham, having observed at different times, and during 
* See Thiout, Traité de’ Horlogerie, pl. 39. fig. 5—T.S. E. 
¢ Philosophical Transactions. 
the 
