138 Le Roy's Memoir on the lest Method ; 
gency of the case, and which we may make to describe a 
Jarge space, Pepe us to regulate the machine to the greatest 
nicety, 
If the effects of he and cold were less bs the incon- 
venience | have just explained might be neglected; but as 
the machine is in a state of trial during more than. six months 
together, it is clear that as the vibrations of different extent 
of the regulator have not then the requisite isochronism, the 
causes which may make the magnitude of these vibrations 
vary, would alter the bai Re of- the clock considerably. 
Convinced of the principle I. have just established, to com- 
pensate the effects of different temperatures in my machine, 
T took a method altogether new. 
I anap'ed to the balance several small bars of copper and 
stecl, disposed in such a‘manner, that, BY, their Jengthening 
or cael in heat and cold, they make to approach or 
recede.from its centre, two considerable parts of its mass, 
each placed at the extremity of a lever, and diametrically op- 
posite. By the computation which I had made, it sufficed 
that the total mass of the balance should approach or recede 
from the centre by about the thirteenth of a line, to com- 
pensate a variation in heat, which would produce one of 15, 
seconds per hour in the rate of the watch, 
One inconvenience of the preceding method made me 
abandon this presently ; the play of the levers, and the small 
solidity of the balance, produced errors greater than those 
which [ wished to compensate; this made me have recourse ° 
to_a third method, which completely succeeded, 
Tt consists in applying to the balance two small thermo- 
meters ¢¢ttt, &c. (Plate III. fig. 6.), each made of a tube 
of bent glass, open at O, fig. 7. These thermometers, com- 
posed of mercury and spirit of wine, would each form an 
exact parallelogram, if the upper side which carries the ball, 
in which is comtained the spirit of wine as well as in this 
side, were not a little inclined. Both these thermometers 
are firmly adjusted and placed on opposite sides of the arbor 
of the regulator, so that the axes of their tubes and that of 
the balance are in the same plane that cuts the balls through 
the middle. . 
It is easy to conceive how this construction produces the 
required 
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