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Coming of Electric Lighting 217 The phenomenon is capable of simple explanation. The electric current heats up the points of the carbon to such an extreme degree as to render the charcoal incandescent. Moreover, the space created between the two opposing points by moving the rods apart— across which the current leaps—becomes charged with a kind of cloud or vapour. In reality this gap becomes filled with an enormous number of extremely minute particles of carbon detached from the two charcoal rods. This microscopic carbon dust is maintained in a condition of extreme incandescence, and thus forms an apparent flame. As may be supposed, Davy’s fascinating experi- ment and demonstration aroused intense scientific interest; but at that time it was impossible to develop its utilisation in such a manner as to make wide public appeal. The fact that batteries constituted the only known means of supplying the requisite current was an insuperable obstacle. Davy’s work, however, was of inestimable value from the scientific point of view, and even at that date he contributed information concerning arc-lighting which otherwise would have had to be discovered in later years before such a system of illumination could have aspired to win popular favour. Although the particles of carbon are detached from the rods and continue the whole while the current is passing, Davy showed that the wearing away is not equal for the two rods. The erosion, or burning away of the rod fed with positive electricity, proceeds twice as rapidly as the decomposition of the negative rod. Moreover, under the passage of the current the ends of the two rods undergo considerable