NATURAL PHILOSOPHY. 141 



has not merely brought into view, but full}' established, the existence of a 

 very extraordinary periodicity in the extent of fluctuation of all the magnetic 

 elements, which connects them directly with the physical constitution of the 

 Sun, and with the periodical greater or less prevalence of spots on its surface, 

 the maxima of the amount of fluctuation corresponding with the maxima 

 of the spots, and these again with those of the exhibitions of the Aurora 

 Borealis, which thus appears also to be subject to the same law of periodicity. 

 The discovery made by General Sabinc of a decennial period in all those 

 magnetic influences at the surface of the globe, which, by their dependence 

 on the hours of solar time, led him to recognize the Sun as their primary 

 cause operating, however, in some other manner than by its heat was 

 explained by reference to the observations of Arago on the diurnal variation 

 of the declination, which were purposely selected by the lecturer, as giving 

 independent evidence on the subject, having been made before the establish- 

 ment of the British Magnetic Observatories, and because that philosopher 

 was evidently unaware of the existence of the periodicity they demonstrate, 

 in common with the later and different observations in which the decennial 

 period was first recognized by Sabine. A general view was then taken of the 

 phenomena of the Solar Spots, and of the analogy between them and the 

 revolving storms of our own atmosphere first inferred by Sir John Hcrschcl, 

 and since remarkably confirmed, it was stated, by the observations of the 

 Rev. R. Dawes on the rotation of the spots about their own centres, and 

 those of Mr. Carrington on the .currents in which they appear to drift across 

 the Sun; and the discovery of a decennial period in their amount and fre- 

 quency by Schwabc of Dessau, in the observations which he has carried on 

 for the third part of a century, was described by reference to tables compar- 

 ing the periods of the maxima and the minima of the spots with those of the 

 magnetic fluctuations as made known by Sabine, which were thus shown to 

 be, when complete, corresponding periods of -ten years. The enormous ac- 

 tivity in certain regions of the S'uu indicated by the magnitude of the spots, 

 and the rapidity of their motions and changes, it was suggested, was ade- 

 quate to any conceivable exertion offeree upon the Earth. In proceeding to 

 the third subject of this law of periodicity, the Polar Lights, after a brief 

 description of their characteristic phenomena, Mr. Braylcy stated that, in 

 his opinion, the only suggestion of their cause, hitherto enunciated, in the 

 nature of a vera causa, had been made by Professor Faraday, and had been 

 amply verified by facts subsequently observed, a statement now made for 

 the first time. In the Bakerian Lecture, read before the Royal Society in 

 1832, relating his discovery of terrestrial magneto-electric induction, Mr. 

 Faraday shoAved that effects similar to those he had obtained by instrumen- 

 tal means, but infinitely greater in force, might be produced by the action of 

 the globe, as a magnet, upon its own mass, in consequence of its diurnal 

 rotation; and, in the sequel, he asked whether the Aurora Borealis and Aus- 

 tralis might not be the discharge of electricity, thus urged towards the poles, 

 and endeavoring to return, above the earth, to the equatorial region; citing, 

 as in accordance with an affirmative reply, the effect of an aurora upon the 

 magnetic needle recorded by Mr. R. "NV. Fox. lie did not pursue the subject; 

 but the hypothesis has been abundantly verified, with respect to the produc- 

 tion of terrestrial currents of electricity, in the manner inferred, by the 

 earth's rotation, and the other natural motions of conductors cutting the 

 magnetic curves, by facts which the electric telegraph, land and submarine, 

 has disclosed, and some of which were recited; while all the phenomena of 



