196 Le Roy’s Memoir on the best Method 
lished and thoroughly hard: three days afterwards this plate 
was worn at the place of the pivot; the arc of vibration was 
considerably diminished ; the freedom of the balance, con 
sequently, very much altered; and the accuracy of the ma- 
chine destroyed. I substituted for the steel plate a polished 
agate, and the same effect again took place. Lastly, to see 
whether when the weight of the balance was diminished on 
the agate the wear would not cease, I replaced the suspen- 
sion wire, I attached its upper extremity to a lever, and I 
put a weight on the other arm of this lever, so that the ba- 
Jance, exceeding the weight a little, rested very gently on 
the plate of steel or the agate. Notwithstanding this pre- 
caution, the freedom was again very much altered by this’ 
slight friction; the plate and the agate both wore, although 
“much less than before; whence arose the inconveniences 
above mentioned. It appears, therefore, absolutely neces- 
sary in these kinds of works that the regulator should be 
suspended by a harpsichord wire, as the foliot was formerly 
‘by two threads of hemp or silk. 
In the first attempts which I made with this machine, 
nearly twelve years ago*, instead of using a harpsichord 
wire to suspend it, I used a piece of thin narrow spring. 
Several experiments (by which I found that the different vi- 
brations of a body thus suspended were much more isochro- 
nous than those procured to the same body by a spiral 
spring) induced me to make the regulating spring of my 
watch of this suspension spring, and to omit the spiral 
spring: but I soon perceived that to approach isochronism 
nearly, it would be necessary that this regulating and sus- 
pending spring should be very long; this would render the 
machine yery unwieldy in a ship. At last I arrived at the iso- 
chronism of the vibrations, by combination and a certain pro-~ 
portion between the spiral spring (of which I found the long 
vibrations slower than the short) and the suspension spring; 
which gave me, on the contrary, the short vibrations slower 
than the long. This method, like the preceding, required 
a very long suspension spring ; whence arose various incon- 
tie 
* See the sealed paper which I left with the secretary to the Academy in 
1754, The Exposé succinct, &e, p. 40 and 42, 
veniences, 
