MATHEMATICS AND NATURAL PHILOSOPHY. 233 



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 fluctua- 

 tion 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 Sabine 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 pri- 

 mary 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 indepen- 

 dent evidence on the subject, having been made before the establishment 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 diSerent 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 Herschel, 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 

 frequency by Schwabe of Dessau, in the observations which he has carried on for 

 the third part of a century, was described by reference to tables comparing 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 com- 

 plete, corresponding periods of ten years. The enormous activity in certain 

 regions of the Sun, indicated by the magnitude of the spots, and the rapidity of 

 their motions and changes, it was suggested, was adequate to any conceivable 

 exertion of force 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. Brayley stated that, in his opinion, the only suggestion of their 

 cause hitherto enunciated, in the nature of a vera causa, had been made by Profes- 

 sor 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 induc- 

 tion, Mr. Faraday showed that effects similar to those he had obtained by instru- 

 mental 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 Australis might not 

 bo the discharge of electricity thus urged towards the poles, and endeavouring to 

 return, above the earth, to the equatorial regions ; citing, as in accordance with 

 an affirmative reply, th effect of an aurora upon the magnetic needle recorded by 

 Mr. R. W. Fox. He did not pursue the subject ; but the hypothesis has been 

 abundantly verified, with respect to the production of terrestrial currents of elec- 

 tricity, 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 



