aperture, C, which is made to coincide with one of the divisions. This
division corresponds to the number of equal or proportional parts into
which the circle is to be divided. The slide is provided with a wheel, E,
that carries a point which serves at every revolution to trace the points
that indicate the divisions of the circumference.

[Illustration: FIG. 1.--MODE OF USING THE CIRCLE DIVIDER. ]

The apparatus operates as follows: Suppose, for example, that it becomes
necessary to divide a circumference into 19 equal parts: We make the
aperture, C, coincide with the 19th division of the rule, and fix the
point of the rod, T, in the center of the circumference, and cause the
rule to revolve around it. The wheel, E, will revolve upon its axis, g,
and, at every revolution, its point will make a mark which corresponds to
the 19th part of the circumference--

Circumf. c / Circumf. C = r / R

It is always necessary that the extremity of the wheel, E, and the
center-point, T, shall be at the same height in order to have the
divisions very accurate.

[Illustration: FIG. 2.--THE CIRCLE DIVIDER. ]

* * * * *




SOLUBLE GLASS.