Bright sparks should never be allowed to appear at the commutator and brushes, as sparks result from a rapid burning of the metallic parts. They can easily be avoided by properly inclining the two arms which carry the brushes.
The position of the brushes yielding the least spark at the commutator is that giving the highest intensity of light in the electric arc.
The commutator should, while in motion, be freely oiled, to prevent the brushes wearing away too rapidly. The sticky oil should from time to time be removed by washing with paraffine oil or benzoline.
Wear and Tear.—The chances of stoppage so common to the old forms of electric light apparatus have in this form been reduced to a minimum, and now do not exceed those that arise with machines generally. The Trinity House Report states that the Siemens' machine worked well for a month without any necessity for stopping. The brushes are the only parts which wear away, and they are very easily replaced.
In thick weather they should be connected in what is called parallel circuit (or parallel arc, or for "quantity"), because it has been found that when they are so arranged the intensity of the electric light produced exceeds by some twenty per cent. the intensity of the sum of the two when worked separately. Thus the two machines, giving respectively a candle power of 4,446 and 6,563 when worked separately (total 11,009), have given when coupled up in parallel circuit a light equivalent to 13,179 candles; just as in telegraphy it has been found that the rate of sending can be increased from 20 to 25 per cent. when the apparatus is coupled up in parallel arc. For this reason it is usual to employ two machines of medium size instead of one machine of large size. The intense light so produced is also much more uniform than from one large machine.
Automatic Electric Lamp.—Automatic electric lamps have been constructed with spring clockwork to cause the carbons to approach one another to a certain point, when, by means of an electro-magnet, the clockwork is checked, and the carbon points are allowed to burn away to such a distance that, by the decrease of current, the clockwork is released and the carbons caused to approach again. With such lamps the clockwork has been a source of trouble, and it is liable to get out of order.
Siemens' Patent Electric Lamp.—The lamp here described is actuated without clockwork; it also automatically separates the carbons after they have approached too closely or touch, and, by this combined action of approaching and separating, the carbon points are kept at a proper distance apart, and a steady light is obtained.
The working parts are represented in the diagram [Fig. 169], and at [Fig. 170] is shown the size employed on board ship.
E is the horse-shoe magnet with the armature A placed in front of its poles a short distance from them. A regulating screw b with the spiral spring f is attached to the lever A', forcing it against the stop d, and withdrawing the armature from the poles of the electro-magnet. When a current traverses the coils of the latter of sufficient strength to attract the armature and overcome the tension of the spring f, contact is made at c, which diverts the current from those coils. The consequent release of the armature breaks contact at c, the armature is again attracted, and this action is repeated, producing a vibrating motion of the lever and armature, which continues as long as there is sufficient current to overcome the tension of the spring.