250 MAGNETIC STORMS. 



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 excita- 

 tion 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 magne- 

 tism,, and we appear to have within our grasp the ex- 

 planation AVC 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 phos- 

 phorescence ; and by the slightest change of tempera- 

 ture we may produce that play of colours which is 

 sometimes so remarkably manifested in Aurora. Dr. 

 Dalton considered Aurora borealis as a magnetic pheno- 

 menon, 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.* 

 It is, therefore, yet a question for our consideration, 

 does the earth's magnetism produce the peculiar pheno- 



* Faraday : On the Diamagnetic character of Flame and Gases. 



