Even in November they feared to work by day, lest the sun's rays acting on the gun-cotton might lead to unhappy results. This led to their working at night, by light produced in a vacuum by means of Ruhmkorff's apparatus, which threw an artificial brightness into the depths of the Columbiad. There the cartridges were arranged with the utmost regularity, connected by a metallic thread, destined to communicate to them all simultaneously the electric spark, by which means this mass of gun-cotton was eventually to be ignited.