THE SUN. 79 



the magnetism of the earth ; which we all know to be 

 the cause of the compass needle pointing to the north. 

 This is only a rough way of speaking. It does not 

 point to the north, but very considerably to the west of 

 north, and that, not always alike. Three centuries ago 

 it pointed nearly as much east as now west of north. 

 From year to year the change is very perceptible ; and, 

 what is more, at every hour of the day there is a small 

 but perfectly distinct movement to and fro, eastward and 

 westward, of its average direction. But besides this, the 

 compass needle is subject to irregular, sudden, and ca- 

 pricious variations jerking, as it were, aside, and oscil- 

 lating backwards and forwards without any visible cause 

 of disturbance. And, what is still more strange ; these 

 disturbances and jerks sometimes go on for many hours 

 and even days, and often at the same instants of time, 

 over very large regions of the globe ; and in some 

 remarkable instances, over the whole earth the same 

 jerks and jumps occurring at the same moments of time 

 (allowance made for the difference of longitude). These 

 occurrences are called magnetic storms, and they invari- 

 ably accompany great displays of the Aurora ; and are 

 very much more frequent when the sun is most spotted, 

 and rarely or never witnessed in the years of few spots. 



(37.) The last four years* have been remarkable for 

 spots, and there occurred on the ist September 1859, an 

 appearance on the sun which may be considered an 

 epoch, if not in the sun's history, at least in our know- 



* This lecture was delivered about the end of 1861. 



