M. Planté has performed some experiments with a very considerable series of secondary batteries. By inserting the positive electrode after the negative in a vessel of salt water, luminous and other effects were observed which were considered to have a strong resemblance to those of Auroræ. M. Planté advocates the theory that the imperfect vacuum of the upper regions, acting like a large conductor, plays the part of the negative electrode in his experiments, while the positive electricity flows towards the planetary spaces, and not towards the ground, through the mists and ice-clouds which float above the Poles. [Sidenote: M. Planté’s experiments producing a corona, an arc, or a sinuous line.] 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. [Sidenote: Mr. Holden’s views.]