(3) A galvanic current going in an opposite direction to that of the discharge, and having its origin in the electromotive force discovered by M. Edlund in the electric spark. That these currents require a closed circuit; but this is not necessary in the case of the Aurora, as the earth and rarefied air of the upper regions are immense reservoirs of electricity producing the same effect as if the circuit were closed. That permanent moisture in the air, a good conductor of electricity, is the cause of a slow and continuous discharge assuming the form of an Aurora, instead of suddenly producing lightning as in equatorial regions and mean latitudes. [Sidenote: Polar Light due to electric discharges only.] He sums up, that the electric discharges which take place in the Polar regions between the positive electricity of the atmosphere and the negative electricity of the earth are the essential and unique cause of the formation of the Polar Light, light the existence of which is independent of terrestrial magnetism, which contributes only to give to the Polar Light a certain direction, and in some cases to give it motion. This Prof. Lemström maintains contrary to those who believe they see in terrestrial magnetism, or rather in the induction currents, what is capable of developing the origin of the Polar Light. _Theories of MM. Becquerel and De la Rive._ [Sidenote: Theories of MM. Becquerel and De la Rive.] M. Becquerel’s theory is that solar spots are cavities by which hydrogen and other substances escape from the sun’s protosphere. That the hydrogen takes with it positive electricity which spreads into planetary space, even to the earth’s atmosphere and the earth itself, always diminishing in intensity because of the bad conducting-power of the successive layers of air and of the earth’s crust. That would then only be negative, as being less positive than the air. The diffusion of electricity through planetary space would be limited by the diffusion of matter, since it cannot spread in a vacuum. That gaseous matter extends further than the limits usually assigned to the earth’s atmosphere, is proved by the observation of Auroræ at heights of 100 and 200 kilometres, where some gaseous matter must exist. M. de la Rive agrees with M. Becquerel as to the electric origin of the Aurora, but considers the earth is charged with negative electricity and is the source of the positive atmospheric electricity, the atmosphere becoming charged by the aqueous vapour rising in tropical seas. The action of the sun he considers is an indirect one, varying with the state of the sun’s surface, as shown by coincidences in the periods of Aurora and sun-spots. _M. Planté’s Electric Experiments._ [Sidenote: M. Planté’s experiments. Effects produced resembling Auroræ.]