We have now our two centers established, whose
peripheries are in the relation of 2 to 1.
To know, in the chronometer which we are supposed to be constructing,
the exact distance apart at which to plant the hole jewels for our two
mobiles, i.e., escape wheel and balance staff, we measure carefully on
our drawing the distance from _a_ to _c_ (the latter we having just
established) and make our statement in the rule of three, as follows: As
(10) the diameter of drawn escape wheel is to our real escape wheel so
is the measured distance on our drawing to the real distance in the
chronometer we are constructing.
It is well to use great care in the large drawing to obtain great
accuracy, and make said large drawing on a sheet of metal. This course
is justified by the degree of perfection to which measuring tools have
arrived in this day. It will be found on measurement of the arc of the
circle _B_, embraced between the intersections _e e^2_, that it is
about forty-eight degrees.
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