The Poetry of Science; or, Studies of the Physical Phenomena of Nature

by Robert Hunt

That the part of the sky where all the beams of the Aurora unite, is that to which a magnetic needle directs itself, when suspended by its centre of gravity:—

That the concentric circles, which show themselves previously to the luminous beams, rest upon two points of the horizon equally distant from the magnetic meridian; and that the most elevated points of each arch are exactly in this meridian.[181]

It does not appear that every Aurora disturbs the magnetic needle; as Captains Foster and Back both describe very splendid displays of the phenomenon, which did not appear to produce any tremor or deviation upon their instruments.[182]

Some sudden and violent movements have been from time to time observed to take place in suspended magnets; and since the establishment of magnetic observatories in almost every part of the globe, a very remarkable coincidence in the time of these agitations has been detected. They are frequently connected with the appearance of Aurora borealis; but this is not constantly the case. These disturbances have been called magnetic storms; and over the Asiatic and European continent, the islands of the Atlantic and the western hemisphere, they have been proved to be simultaneous.

From observations made at Petersburg by Kupffer, and deductions drawn from the observations obtained by the Magnetic Association, it appears probable that these storms arise from a sudden displacement in the magnetic lines of the earth’s surface; but the cause to which this may be due is still to be sought for.

In the brief and hasty sketch which has been given of the phenomena of terrestrial magnetism, enough has been stated to show the vast importance of this very remarkable power in the great operations of nature. We are gradually reducing the immense mass of recorded observations, and arriving at certain laws which are found to prevail. Still, the origin of the force, whether it is strictly electrical, whether it is the circulation of a magnetic fluid, or whether it is merely a peculiar excitation of some property of matter, are questions which are open for investigation.

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.

As electricity has the power of altering the physical conditions of the more adherent states of matter, thus giving rise to variations of form and modes of combination, so gross matter appears to alter the character of this agency, and thus disposes it to the several modifications under which we have already detected its presence. We have mechanical electricity and chemical electricity, each performing its great work in nature; yet both manifesting conditions so dissimilar, that tedious research was necessary before they could be declared identical. Magnetic electricity is a third form; all its characteristics are unlike the others, and the office it appears to perform in the laboratory of creation is of a different order from that of the other states of electrical force. In the first two we have decomposing and recombining powers constantly manifested—in fact, their influences are always of a chemical character; but in the last it appears we have only a directive power. It was thought that evidence had been detected of a chemical influence in magnetism; it did appear that sometimes a retarding force was exerted, and often an accelerating one. This has been again denied, and we have arrayed in opposition to each other some of the first names among European experimentalists. The question is not yet to be regarded as settled; but, from long and tedious investigation, during which every old experiment has been repeated, and numerous new ones tried, we incline to the conclusion that chemical action is not directly affected by magnetic power. It is highly probable that magnetism may, by altering the structural arrangement of the surface, vary the rate of chemical action; but this requires confirmation.[185]