BORNHARDT'S ELECTRIC MACHINE FOR BLASTING IN MINES.


We shall not attempt to pass in review the several apparatus that have
hitherto been devised for igniting blasts in mining operations, but
shall simply describe in this place a machine recently invented for
this purpose by Mr. Bornhardt, an engineer to the Grand Duke of
Brunswick.

This apparatus (shown in the accompanying engravings) consists
essentially of two hard-rubber disks, A (Figs. 2 and 3), keyed to an
iron axle, and of two rubbers, B, that are formed of skin and are held
against the disks by small springs, R; motion is communicated to the
axle, _a_, by means of a pair of gearings, _a_ and _b_, and a crank,
_f_.

[Illustration: BORNHARDT'S ELECTRIC MACHINE FOR BLASTING IN MINES.]

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