In an article in ‘Nature,’ March 14, 1878, a further account is given of M. Planté’s experiments, under the head of “Polar Auroræ;” and it is stated that, in these experiments, the electric current, in presence of aqueous vapour, yielded a series of results altogether analogous to the various phases of Polar Auroræ. If the positive electrode of the secondary battery was brought into contact with the sides of a vessel of salt water, there was observed, according to the distance of the film (electrode?) from the liquid, either a corona formed of luminous particles arranged in a circle round the electrode (fig. 2, p. 90), an arc bordered with a fringe of brilliant rays (fig. 3), or a sinuous line which rapidly folded and refolded on itself (fig. 4). This undulatory movement, in particular, formed a complete analogy with what had been compared in Auroræ to the undulations of a serpent, or to those of drapery agitated by the wind. The rustling noise accompanying the experiment was analogous to that sometimes said to accompany Auroræ, and was caused by the luminous electric discharge penetrating the moisture. As in Auroræ, magnetic perturbations were produced by bringing a needle near the circuit, the deviation increasing with the development of the arch.
The Auroræ were produced by positive electricity, the negative electrode producing nothing similar.
Illustrations of these miniature Auroræ are given in ‘Nature,’ and reproduced on p. 90. No mention of any spectroscopic observations is made.
Mr. Holden’s views.
In a communication to the Metropolitan Scientific Association (‘Observatory,’ March 1, 1879, p. 389), Mr. A. P. Holden, after supporting the theory of a connexion between the waxing and waning of the solar corona and sun-spots, adopts Mr. F. Pratt’s hypothesis “that the Aurora is simply light filmy cirrus cloud, first deposited at the base of a vast upper body of highly rarefied vapour, and illuminated by the free electricity escaping in the condensation through the very rarefied medium above, towards the north or south. The Aurora would, according to this theory, have its origin in a vast electrical storm, resulting from a violent condensation of vapour which causes a flow of electricity from the pole to restore equilibrium.” The Aurora would thus, in Mr. Holden’s opinion, “depend on storm phenomena of an intense character; and the frequency of Auroræ at the sun-spot maxima would indicate the connexion of the latter with the weather.”
Fig. 2. The corona.
Fig. 3. The arc and rays.
Fig. 4. The sinuous line.