The commutator is peculiar, consisting of only three segments of a copper ring, while in the simplest of other continuous current generators several times that number exist, and frequently 120! segments are to be found.  These three segments are made so as to be removable in a moment for cleaning or replacement.  They are mounted upon a metal support, and are surrounded on all sides by a free air space, and cannot, therefore, lose their insulated condition.  This feature of air insulation is peculiar to this system, and is very important as a factor in the durability of the commutator.  Besides this, the commutator is sustained by supports carried in flanges upon the shaft, which flanges, as an additional safeguard, are coated all over with hard rubber, one of the finest known insulators.  It may be stated, without fear of contradiction, that no other commutator made is so thoroughly insulated and protected.  The three commutator segments virtually constitute a single copper ring, mounted in free air, and cut into three equal pieces by slots across its face.  Four slit copper springs, called commutator brushes or collectors, are allowed to bear lightly upon the commutator when it revolves, and serve to take up the current and convey it to the circuit.  These commutator brushes are carried by movable supports, and their position is automatically regulated so as to control the strength of the developed current—­a feature not found in other systems.  This feature, as well as the fact that the commutator can be oiled to prevent wear, saves attendance and greatly increases the durability of the wearing surfaces, while the commutator brushes are maintained in the position of best adjustment.  The commutator and brushes, in consequence, after weeks of running, show scarcely any wear.

THE AUTOMATIC CURRENT REGULATOR.

This consists of a peculiar magnet attached to the frame of the generator, and the movable armature of which has connections to the supports of the commutator brushes for controlling their position.  The regulator magnet is so formed as to give a uniform attraction upon its armature in different positions.  In Thomson’s improved form this is accomplished in a novel manner by making the pole of the magnet paraboloidal in form, and making an opening in the movable armature to encircle said pole.

[Illustration:  THE CURRENT REGULATOR]

The armature is hung on pivots so as to be free to move only toward and from the regulating magnet on changes in the current traversing the latter, and being connected to the commutator brushes, automatically adjusts their position.  By this means the power of the generator is adapted to run any number of lights within its limit of capacity, or may be short circuited purposely or by accident without difficulty arising therefrom; and a number of instances have occurred where the injurious effects of a short circuit accidentally