f carbonic acid, five of watery
vapor, one of oxygen, and three of nitrogen, while the addition of seven
more parts of free carbon to the mixture causes the development, by
explosion, of thirteen volumes of carbonic oxide, five parts of watery
vapor, and three of nitrogen, or twenty-one volumes of gas in place of
fifteen. As the power of an explosive depends principally on the amount
of gas which results from its sudden combustion, it was evident that the
addition of pure or nearly pure carbon, in a condition to be readily
combined with the other elements, ought to increase materially the force
of nitro-glycerine, and M. Roca experimented accordingly with an
admixture of sugar, as a highly carbonized body immediately available,
and found that three parts of this, mixed with seven parts of
nitro-glycerine, detonated with a force from thirty to thirty-five per
cent. greater than that of pure nitro-glycerine. Many other organic
carbonaceous substances may be employed in place of sugar, with various
advantages. In comparing these simple compounds with the celebrated
explosive gum, prepared by dissolving gun-cotton in nitro-glycerine, it
is found that the latter is far inferior, having an energy very little
superior to that of pure nitro-glycerine.

* * * * *

THE CIRCLE-DIVIDER.

This little apparatus, invented by Prof. Mora, of Senlis, permits of
dividing circumferences or circles into equal or proportional parts. It
consists (Fig. 2) of a rule, A, divided into equal or proportional parts,
which pivots in the manner of a compass around a rod, T, that serves as a
central rotary point. Along this rule moves a slide, R, provided with an
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