Suppose next that the points of heating, and with them the alternate points of cooling 90 deg. apart, are shifted round about 45 deg., so that the two hot regions are no longer symmetrically situated in respect to each pole of the field.  The distribution of the magnetization has therefore become unsymmetrical, and the iron core is no longer in equilibrium in the magnetic field.  We have, in fact, the conditions of Schwedoff’s experiment upon a larger scale, and if the forces are sufficient to overcome the frictional resistance, a rotation of the ring ensues in the endeavor to restore equilibrium.  The regions of heating and cooling being fixed in space, this rotation is continuous so long as the difference of temperature is maintained.  The ring in rotating carries with it the armature coils, and of course an E.M.F. is generated in the same way as if the motive power came from an external source.  In this respect the machine therefore resembles a motor generator, and the rotation is entirely automatic.

The armature coils are connected with a commutator in the usual way, and the field may, of course, be excited either in shunt or in series.  M. Menges says that the residual magnetization is sufficient in his machine to start the rotation by itself.

When the machine is to be used as a motor, it is evident that the windings on the armature core need only be sufficient to supply current to excite the field, or by the use of permanent magnets they may be dispensed with altogether.

M. Menges has further designed a large number of variations on the original type, varying the arrangement of the several parts, and employing armatures and fields of many different types, such as are already in use for dynamos.

In Fig. 4 a machine is represented in which the field is external to the armature.

[Illustration:  Fig. 4.]

In Fig. 5 we have a thermo-magnetic generator, which corresponds to the disk machine in dynamos.  Similar parts are indicated by the same letters in each of these figures, so that no further detailed description is necessary.

[Illustration:  Fig. 5.]

In another modification M. Menges proposes to rotate the burners and leave the armature and distributor at rest.  But in this case it is evident that the E.M.F. produced would be much less, because the magnetization of the core would only undergo a variation of intensity, and would nowhere be reversed, except, perhaps, just in front of the poles.  In machines modeled on the Brush type it is evident that the distributor need not be continuous.

Enough has, however, been said to indicate the extent of the field upon which the principle may be applied.—­The Electrician.

* * * * *

OBSERVATIONS ON ATMOSPHERIC ELECTRICITY.[1]

   [Footnote 1:  Abstract of a paper read before the British
   Association meeting at Manchester, September, 1887.]