According to the modern theory of electricity, metallic bodies, far from attracting the electric fluid, as is commonly believed, are of all bodies those which have the least attraction for that fluid, and being the best conductors for it, are entirely passive during its transit through them. In confirmation of these views, the author describes experiments in which the electric spark was found to have penetrated through the side of a glass globe blown to an extreme degree of thinness. An electric jar, from which the air had been partially exhausted, could not be made to receive as high a charge as when the contained air was of the usual density, and when entirely exhausted could not be charged in any sensible degree; when filled with condensed air on the other hand, it retained a higher charge than before. The heated and consequently rarefied air surrounding a red-hot iron rod is found to conduct electricity with great facility. The same property is observed in the flame from a blowpipe, which may be regarded as a hollow cone containing highly rarefied air; as also, in a larger scale, in that of a volcano. Sir H. Davy had concluded from his experiments on voltaic electricity, that the conducting powers of metals are diminished by heat; but Mr. Ritchie infers from several experiments which bear more directly upon the question, that the metals afford no exception to the general law, that in all bodies heat increases the conducting powers; and explains the apparent anomaly in Sir H. Davy’s experiments, by the dissipation of the electricity by the rarefied air surrounding the heated metals, which were used as conductors. He concludes his paper by describing an experiment which appears to establish, in respect to this law, a striking analogy between the electric and magnetic influences.
Luminous vapour from the mercury arc and the progressive changes in its spectrum
