65 



This period, observed in all the magnetic elements, precisely- 

 corresponded with that discovered by Schwabe for the number 

 of solar-spots. 



This isochronous periodicity has been further proved by 

 M. Gautier, of Geneva, and M. Wolfs, of Zurich, each un- 

 acquainted with the other's researches, and ignorant of the 

 observations of Sabine, Hanstein, &c. 



Since these discoveries have been made, other relations of 

 a different kind have been found to exist between the solar- 

 spots and the position of other planets in the system ; not 

 only the number or mpgnitude of the spots, but their position 

 also is in part dependent on the places of the planets in space. 

 The belief that the earth is a great magnet is of very ancient 

 date, and the same power may be conceded to the other 

 planets as being governed by the same laws. This was the 

 opinion of Euler, Tobias Mayer, and Hanstein ; next came 

 Gaus, whose system of terrestrial magnetism was what Newton's 

 theory was to the solar system, as the law of magnetic force 

 varies in inverse ratio of the square of the distance — just as is 

 the case with universal attraction. The result of M. Gaus' 

 investigations was a close agreement between theory and 

 experiment. 



There is, however, another phenomenon recognised in the 

 Aurora, which is found to be produced by electro- magnetism, 

 and is connected with the spots on the sun, their maxima 

 and minima corresponding in every case. 



It will be remembered by many members of the Society that 

 on the 14th March, 1860, I had the honour to read, in connec- 

 tion with Colonel Broughton, E.E., a paper on " Atmospheric 

 Electricity." At that time solar-spots were at a maximum, and 

 there were some very beautiful displays of Aurora Austral is. 

 In the paper referred to I ventured on the following theory, 

 viz., that the rapid rotation of the earth on its axis engendered 

 a large amount of terrestrial magnetism at the poles, which 

 becoming connected with atmospheric electricity, produced the 

 beautiful corruscations which were then seen. My observations 

 were sent home by Dr. Milligan, and forwarded to Professor 

 Loomis, whose investigation of these and other records of the 

 same nature enabled him to trace a period of about ten years 

 for the maximum of sun-spots, of terrestrial magnetism, and 

 of auroral displays. 



Soon after that paper reached London I received a compli- 

 mentary letter from a scientific meteorologist, who agreed 

 with everything it contained except the theory of theproduction 

 of the Aurora. Since that time, however, and onlv latelv 

 (December, 1869), Mr. Balfour Stewart, Director of Kew 

 Observatory, read a paper before the Koyal Afcitronoraleal 



