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, 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.