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Elmer Sperry: Electric Searchlight, 1920

Losing No Time

After tackling the task of improving the arc light, Sperry and Bassett began designing the complete searchlight. The inventive pair came up with ingenious ways to ventilate the searchlight housing, known as a drum, to cool, automatically feed, and rotate the electrodes, and to automatically position the positive electrode crater so that it was at the focal point of the reflector mirror. The formation of a deep crater in the positive electrode had been a development of Bassett's. He had achieved this by designing a positive electrode that was composed of two parts: a shell and a core. The material he chose for the core burned faster than that of the shell, enabling the burning core to recess into the shell and form a deep crater in the positive electrode. The arc flame and luminescent gases were confined in this crater, and the concentration of flame and luminescence in the crater resulted in the intensity of the searchlight.