In 1750, Wargentin noticed that a very remarkable display of _Aurora borealis_ was the cause of a peculiar disturbance of the magnetic needle; and Dr. Dalton[180] was the first to show that the luminous rays of the Aurora are always parallel to the dipping-needle, and that the Auroral arches cross the magnetic meridian at right angles. Hansteen and Arago have attended with particular care to these influences of the northern lights, and the results of their observations are:-- That as the crown of the Aurora quits the usual place, the dipping-needle moves several degrees forward:-- 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.