ers of equal diameters the work performed by the former of these
is greater than that done by the second, but in the latter the
expansive force of the steam is better utilized. This comparison seems
to us to be more ingenious than exact. Would it not be coming nearer
to the truth if we were to suppose a case of a hydraulic motor whose
performance continued diminishing with the height of the fall, and
would it not be advantageous under such circumstances to utilize only
a portion of the fall for the purpose of increasing the motor's
performance?

This machine, however, as before stated, has never as yet been
constructed, so that experimental data relative to its mode of working
are wanting. It is especially interesting as regards its origin, which
dates back to an epoch at which researches on the dynamo electric
machine were at their heat. It is in its historical aspect that it is
proper to regard it, and it is from such a point of view that we have
deemed it well to say a few words about it in this place.--_La Lumiere
Electrique._

* * * * *

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
special spring. Another ring, _t_, is connected in the same way wi