Each disk revolves between two metallic rings, c, provided with points that attract and collect in Leyden jars, D, the electricity produced by the friction.  For discharging the condensers there is employed a manipulator formed of a rod, mm, which can be acted upon, from the exterior, by means of a button, k.  Upon bringing the ball, m, of the rod in contact with the ball, p, of the condenser, the lever (which then takes the position shown by the dotted line) continues to remain in connection with a small ring, q, through a special spring.  Another ring, t, is connected in the same way with the external armature of the condenser.  Upon connecting the rings, p and t, by a wire to which cartridges are attached, any number of the latter may be ignited.

The parts that we have just enumerated are inclosed in a tin box covered with a wooden casing, P. Between the two there is inserted a sheet of hard rubber in order to prevent a loss of electricity; the whole is held in place by strong springs.

In order to show the normal state of the condenser, a scale consisting of 15 metallic buttons to give the dimensions of the sparks, is arranged at X. This scale is capable of being connected with the rings, q and t, by means of chains; when the spark obtained after 15 or 20 revolutions considerably exceeds the intervals of the scale, it is a sure thing that the machine is in a proper state.

In order to prepare the apparatus for carriage, the winch is taken off and placed in the compartment, m, which is closed by means of a door, Q.

Figs. 5 and 6 show the arrangement of the dynamite cartridges and wires in the blast hole.  Figs. 7 to 10 show different arrangements of the igniting wires.  Figs. 11 and 12 give the general arrangement for igniting a number of cartridges simultaneously by means of the electric machine.  Fig. 13 shows the arrangement where powder is employed.  Fig. 14 shows the arrangement of a horizontal hole.—­Annales Industrielles.

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IMPROVED ELECTRIC FIRE ALARM.

The object of this apparatus is to close an electric circuit when the temperature of a room rises above a certain point.  Many devices have been invented for effecting this object, each of which have their own advantages or disadvantages.  The invention of Mr. Pritchett enables the required result to be obtained in a very satisfactory manner.  The apparatus consists (as shown by the figure) of a long glass vessel containing air; connected to this vessel there is a glass tube filled with mercury.  The whole is mounted on a metal cradle, which turns on pivots.  According to the position which the glass vessel and its adjuncts occupy in the cradle (this position being adjustable by means of a thumb-screw, seen at the upper part of the cradle), so will the same have a