66 



E. WALTER MAUNDER, F.R.A.S., ON 



and the amount of this oscillation is, roughly speaking, twice as 

 great during years of great solar activity as it is in years of solar 

 quiescence. As the curves representing the areas of sunspots 

 or of faculse mount up, so do the curves representing the daily 

 range of the earth's magnetism mount also ; as the curves of 

 the solar activity decline, so do the curves of the daily magnetic 

 range. 



But this is only a general relationship. There is a particular 

 one, and it fell to my lot to trace it out. My own interest was 

 with sunspots, not with terrestrial magnetism. But in 1882, 

 April, a group of spots appeared on the sun much larger than any 

 that I had seen in nine years' experience, and during its progress 

 across the sun's disc, a remarkable disturbance of the magnetic 

 needles took place, not at Greenwich alone, but at magnetic 

 observatories all over the world. While this great sunspot group 

 was crossing the disc, a second group sprang up, and another 

 great disturbance of the magnetic needles occurred. Then, in 

 the November of the same year, a spot was seen on the sun 

 greater than either of these two, and again a very violent magnetic 

 storm broke out, accompanied by a wonderful display of the 

 aurora borealis. From that time forth, I had no doubt in my 

 own mind that there was a direct connection between these great 

 displays of solar activity and the great displays of activity in the 

 earth's magnetism. 



Other similar coincidences were observed ; there was, for 

 instance, a great magnetic storm in 1892, February 13, when the 

 great group already referred to was a little past the central 

 meridian of the sun's disc. But though sunspot observers were^ 

 in general, convinced that there was a real connection between 

 the two activities, many of the great authorities on terrestrial 

 magnetism took an entirely difierent view, and Lord Kelvin, 

 in his annual address to the Royal Society in that very year, 

 1892, laid it down that the great magnetic storm could not 

 possibly be ascribed to any solar action. Dr. Rudolf Wolf, of 

 Zurich, the most indefatigable observer of sunspots then living, 

 replied to the effect that if physicists said that the connection was 

 impossible, he would not dispute it ; nevertheless, he could 

 affirm that it existed. 



But the connection was not easy to establish. It often happened 

 that a great sunspot would pass across the sun's disc and the 

 magnetic needle would make no sign ; it sometimes happened 

 that the magnetic needles would be disturbed and the sun present 



