The spring pawl s at the upper end of the lever A', and oscillating with it, actuates a ratchet-wheel u, which is in gear with a train of wheels and the carbon holders; it thus opposes their tendency to approach by pushing them apart, tooth by tooth, until the current is so much weakened by the increased length of electric arc that the armature and lever cease to oscillate enough to move the teeth of the ratchet-wheel, and it rests near the stop d.
While in this position the spring pawl is released from the ratchet-wheel and the preponderating weight of the upper carbon holder causes the carbon points to approach again. Increase of current follows decrease of resistance, the armature again oscillates, and this cycle of action is continuously repeated.
When in action the movements of the carbons are scarcely perceptible, but when, by any external cause, the carbons are separated so as to extinguish the light, they immediately run together until they touch, when they ignite and separate to a proper working distance by means of the electro-magnet above described.
The only operation requiring attention in the use of this lamp is the adjustment of the tension of the spring f. When this tension is once regulated to the current at disposal, the lamp will continue to give a steady light as long as the current remains uniform.
The relative rate of consumption of the two carbon points differs. The positive carbon burns away rather more than twice as quickly as the negative carbon.
