and that he succeeded some
time before Gramme in obtaining continuous currents.

[Footnote 1: _Zeitschrift des Electrotechnischen Vereines_ in
_Wien_, July, 1883.]

The Kravogl motor that figured at the Universal Exhibition of 1867 is
but little known, and it is now very difficult to obtain drawings of
it. What is certain is that this motor is an application of the
properties of the solenoid, and, from this standpoint, resembles the
Bessolo motor that was patented in 1855. We may figure the apparatus
to our mind very well if we suppose that in the Gramme ring a half and
almost two-thirds of the core are removed, and the spirals are movable
around the said core. If a current be sent into a portion of the
spirals only, and in such a way that only half of the core be exposed,
the latter will move with respect to the bobbin or the bobbin with
respect to the core, according as we suppose the solenoid or the
bobbin fixed. In the first case we have a Bessolo motor, and in the
second a Kravogl one.

In order to obtain a continuous motion it is only necessary to allow
the current to circulate successively in the different portions of the
solenoid. It is difficult to keep the core in place, since it is
unreachable, being placed in the interior of the bobbin. Kravogl
solved this difficulty by constructing a hollow core into which he
poured melted lead. This heavy piece, mounted upon rollers, assumed a
position of equilibrium that resulted from its weight, from friction,
and from magnetic attraction. But for a current of given intensity
this position, once reached, did not vary, and so necessitated a
simple adjustment of the rubbers. Under such circumstances, with a
somewhat large number of sections, the polarity of the core was nearly
constant. The spirals as a whole were attached to a soft iron armature
that had the effect of closing up the lines of forces and forming a
shell, so to speak.

Like Bessolo, Kravogl never thought of making anything but a motor,
and did not perceive that his machine was reversible. It results from
some correspondence between Dr. A. Von Waltenhofen and Mr. L.
Pfaundler at this epoch that the latter clearly saw the possibility of
utilizing this motor as a current generator. Under date of November 9,
1867, he wrote, in speaking of the Kravogl motor, which had just been
taken to Innsbruck in order to send it to Paris. "I regret that I
shall not be able to see it any more, for I should have like