— 148 — 

 ANNEXE F. 



(Voir Seance du 28 Juillet 1882, page 75) 

 SDNSPOTS AND TERRESTRIAL MEGNETISM 



Ifc is well known that solar activity is subject to 

 enormous variations. At times, dark spots and bright 

 faculce appear on the sun's surface, and immense 

 protuberances around his limb, while, at other times, 

 these phenomena are rare, or altogether absent. The 

 spots, faculce, and protuberances incre?se from a 

 minimum in one year to a maximum in another, and 

 then decrease to a minimum ; and the mean interval 

 from minimum to minimum, or from maximum to 

 maximum, is 11 years. We are just now at or near an 

 epoch of maximum activity. The last maximum took 

 place in 1870, and the last minimum in 1878. 



Nearly 30 years ago, Sir Edward Sabine and Dr 

 Lamont pointed out that there was apparently a 

 close connextion between changes of solar activity and 

 terrestrial magnetism; a freely suspeded magnetic 

 bar, or needle, being subject to much greater and 

 more frequent deviations from its normal position 

 when solar activity was at its maximum than when it 

 was at its minimum. This was for a long time con- 

 tested, but it is now universally admitted that there is 

 such a connexion. It is found, also, that auroras are 

 much more frequent and extensive at and near the 



