It removes all that sensitiveness to oil which is generally present in such eases. The Thom son-Houston machine can be rim with a steady stream of oil pouring upon the commutator, and, there being no carbonizable material collecting at the commutator segments, no fear of short circuits of armature-coils need be apprehended from that cause.
When used as a generator, the armature-coils successively traverse the opposed field-spaces, and the impulses so produced in them find connection through the commutator-brnshes to the circuit. The armature-helices act for a portion of the time in multiple arc of two coils. as when they are traversing field-spaces where the impulse is considerably below the maximum, and act alone or in series with the other coils, when they are producing their maximum im pulse. These actions necessarily result from the three-coil or three-branched armature system. The mode of application of the brushes is such that when the electromotive force of one branch or coil has fallen below that of the branch or coil which follows it in sequence during rotation, the current is transferred to the latter, and the former coil, although it has not yet reached neutrality, is in stantly put by the commutator into connection with the opposite commutator-brushes, there to act in supplanting that branch which is about to leave said brushes. This mode of carrying off the currents will be understood by reference to Fig. 3-1. It possesses the apparent anomalous condi tion of putting a commutator segment, just before the coil or branch to which it is attached has reached neutrality of electrical action, into momentary contact or electrical connection with both positive and negative brushes of the machine. This condition. however, gives rise to no perceptible in convenience, and this latter fact is ae connted for by the powerful effect of the field-magnet he lices in preserving the volume and di rection of the cur rent at the instant of the emMneetinli Pig referred to.
During reg,ula t ion I he posit ions of the brushes are so altered as to enlarge this period of con nection, and so di minish the available electromotive force of the machine. At the same time, also, the total resistance in circuit being lessened by ex tinction of lights or removal of resistance, while the current-strength remains constant, the energy represented in the main circuit falls in proportion, and the mechanical energy expended in producing the current fails in nearly the same proportion. Speed variations are compen
sated for by the regulator controlling the brushes, as in eases of variations of resistance in circuit.
In the machines for 35 and 50 2,000-candle-power are-lights the ring-armature shown in Fig. 40 has recently been adopted, as it offers many advantages in better ventilation and higher insulation. and, besides, permits of repairs more readily than the older form. The accompanying diagram (1'ig. 41) and table give the various dimensions, weights, and capaci ties of the T homson-11oustou machines : The Ifoehhoomen Dynamo.—The latest type of this machine, intended for arc-lighting, is shown in Fig. 42. The magnetic frame consists of two field-cores connected by a cast-iron yoke at one end and provided with pole-pieces at the of her, which en circle the armature on three sides. The armature, it will be noted, is placed with its shafts in hearings which are on the interior of the machine, so that the armature. as exhibited in Fig. 43, can be entire ly exposed. This is facilitated by the pole-pieces, which are hinged, as shown, and Nv MI can be turned out so as to show the armature completely. and allow it to be drawn out a sufficient distance for thorough repair. if necessary. with out removing the shaft from the journal-bearings. The armat ore core is built up of iron wire, in sulated by paper, the wire being wound on a cast-iron frame or skeleton having a T-section, which divides the core into two parts. The arms of the spider which holds the armature are insulated from' the core and frame, and fit into notches which are cut taper ing from both sides toward the center, so as to keep the hole con centric. The coils of the arma ture, which are rectangular in sec tion. are wound automatically upon the core by an ingenious machine devised by Mr. !loch hausen for that purpose. When placed upon the armature-core the coils are separated on the outer circumference by wooden wedges, which are secured to the east-iron skeleton of the armature, and they are held in position by sections of fiber-band which are screwed into the wooden wedges just referred to.