The generator is known as the “Thomson spherical,” on account of the nearly spherical form of its armature, and differs radically from all others in all essential portions, viz., its field magnets, armature, and winding thereof, and in its commutator; both in principle and construction, and, besides, it is provided with an automatic regulator, an attachment not applied to other generators.  The annexed view of the complete machine will convey an idea of the general appearance and disposition of its parts.

The revolving armature which generates the electrical current is made internally of a hollow shell of soft iron secured to the central portion of the shaft between the bearings, and is wound externally with a copper conducting wire, constituting three coils or helices surrounding the armature, which coils are, however, permanently joined, and in reality act as a single three-branched wire.

This wire, being wound on the exterior of the armature, is fully exposed to the powerful magnetic influence of the field poles, which inclose the armature almost completely.  The armature will thus be seen to be thoroughly incased and protected, at the same time that all the wire upon it is subject to a powerful action of the surrounding magnets, resulting in an economy in the generation of current in its coils.  The form of the armature being spherical, very little power is lost by air friction, and no injury can occur from increased speed developing centrifugal force.  The field magnets, which surround the armature, are cast iron shells, wound outside with many convolutions of insulated copper wire, and are joined externally by iron bars to convey the magnetism.  These outer bars serve also as a most efficient protection to the wire and armature of the machine during transportation or otherwise.  Objects cannot fall upon or rest upon the wire coils and injure them.  The coils of wire upon the field magnets surround not only the iron poles or shells, but are situated also so as to surround likewise the revolving armature, and increase the effect produced in it by direct induction and magnetism.  This feature is not used in any other generator, nor does any other make use of a spherical armature.  The shaft is mounted in babbitted bearings of ample size, sustained by a handsome frame therefor, and is of steel, finely turned and perfectly true.  The shaft and armature together are balanced with the utmost care, and run without buzz or rumble.  The armature wire is kept cool by an active circulation of air over its whole surface during revolution.  The commutator, or portion from which the currents developed in the armature are carried out for use, is a beautiful piece of mechanism.  It is mounted upon the end of the shaft, and has attached to it the wires, three only, coming from the armature wire through the tubular shaft.

[Illustration:  THE THOMSON SPHERICAL.]