In the beautiful Aurora borealis, with its trembling diffusive lights, and its many-coloured rays, we have what may be regarded as a natural exhibition of magnetism, and we appear to have within our grasp the explanation we desire. But we know not the secret of even these extraordinary meteorological displays. If we pass an electric spark from a machine through a long cylinder, exhausted of air as far as possible, we have a mimic representation of the Northern Lights--the same attenuation of brightness, almost dwindling into phosphorescence; and by the slightest change of temperature we may produce that play of colours which is sometimes so remarkably manifested in Aurora. Dr. Dalton considered Aurora borealis _as a magnetic phenomenon, and that its beams are governed by the earth’s magnetism_. We know that the arc of light produced between the poles of a powerful galvanic battery is readily deflected by a good magnet; and we have lately learned that every vapour obeys the magnetic force.[183] It is, therefore, yet a question for our consideration, does the earth’s magnetism produce the peculiar phenomena of Aurora by acting upon electricity in a state of glow? or have we evidence in this display of the circulation of the magnetic fluid around our globe, manifesting itself by its action on the ferruginous and other metallic matter, which Fusinieri has proved to exist in the upper regions of our atmosphere.[184] That magnetic radiations do exist, has been proved by Faraday, and that they form lines of force perpendicular to the earth’s surface, has been experimentally shown. Parallelograms of wire moved upon a central axis, and connected with a galvanometer, give at every revolution indication of an electric disturbance in all respects analogous to the production of a current by moving wires in front of a steel magnet. The alteration in the properties of heat, when it passes from the radiant state into combination with matter, exhibits to us something like what we may suppose occurs in the conversion of magnetism into electricity or the contrary. We have a subtile agent, which evidently is for ever busy in producing the necessary conditions of change in this our earth: an element to which is due the development of many of the most active powers of nature; performing its part by blending with those principles which we have already examined; associating itself with every form of matter; and giving, as we shall presently see, in all probability, the first impulses to combination, and regulating the forms of aggregating particles.