Before we take up the details of drawing an escapement we will say a few
words about "degrees," as this seems to be something difficult to
understand by most pupils in horology when learning to draw parts of
watches to scale. At Fig. 2 we show several short arcs of fifteen
degrees, all having the common center _g_. Most learners seem to have an
idea that a degree must be a specific space, like an inch or a foot. Now
the first thing in learning to draw an escapement is to fix in our minds
the fact that the extent of a degree depends entirely on the radius of
the arc we employ. To aid in this explanation we refer to Fig. 2. Here
the arcs _c_, _d_, _e_ and _f_ are all fifteen degrees, although the
linear extent of the degree on the arc _c_ is twice that of the degree
on the arc _f_. When we speak of a degree in connection with a circle we
mean the one-three-hundred-and-sixtieth part of the periphery of such a
circle. In dividing the arcs _a a_ and _b b_ we first divide them into
six spaces, as shown, and each of these spaces into ten minor spaces, as
is also shown. We halve five of the degree spaces, as shown at _h_. We
should be very careful about making the degree arcs shown at Fig. 1, as
the accuracy of our drawings depends a great deal on the perfection of
the division on the scale _A_. In connection with such a fixed scale of
degrees as is shown at Fig. 1, a pair of small dividers, constantly set
to a degree space, is very convenient.

MAKING A PAIR OF DIVIDERS.

[Illustration: Fig. 3]

To make such a pair of small dividers, take a piece of hard sheet brass
about 1/20" thick, 1/4" wide, 11/2" long, and shape it as shown at Fig.
3. It should be explained, the part cut from the sheet brass is shown
below the dotted line _k_, the portion above (_C_) being a round handle
turned from hard wood or ivory. The slot _l_ is sawn in, and two holes
drilled in the end to insert the needle points _i i_. In making the slot
_l_ we arrange to have the needle points come a little too close
together to agree with the degree spaces on the arcs _a a_ and _b b_. We
then put the small screw _j_ through one of the legs _D''_, and by
turning _j_, set the needle points _i i_ to exactly agree with the
degree spaces. As soon as the points _i i_ are set correctly, _j_ should
be soft soldered fast.

The degree spaces on _A_ are set off with these dividers and the spaces
on _A_ very carefully marked. The upper and outer arc _a a_ should have