72 THE RECENT SUN-SPOTS. 



direction indicated by the magnetic needle undergoes no changes. 

 The fact is that it is in incessant movement. It is true that these 

 movements are generally so small that they do not in the least 

 interfere with the practical utility of the compass. In fact, such 

 changes as those to which I am now referring would not be at all 

 perceptible on an ordinary ship's compass i they would require the 

 refinement of apparatus and observation which I have already 

 indicated. But there is no doubt that incessant fluctuations of 

 the needle are in progress by day and by night, and sometimes 

 it will happen that what is known as a magnetic storm will take 

 place. On such an occasion the needle is thrown into a state of 

 oscillation, which may be described as violent in comparison with 

 the movements which it has on more normal occasions. It has 

 been shown by a careful study of upwards of a hundred magnetic 

 storms, that there is an almost invariable connection between them 

 and some disturbance of the sun's surface. 



It is not at present easy to say what the precise character of 

 that connection may be, but it is absolutely certain that whenever 

 the sun is in a highly disturbed state, as shown by the sun spots 

 and other solar features, that then there is a distinct disturbance in 

 the magnetic state of the eartli. Other similar phenomena can 

 also be cited. Auroras are most usual when the magnetism of 

 the earth is in unusual excitement, and auroras are seen in unusual 

 splendour, and frequently at a time when the sun is in a state of 

 agitation. 



Special instances have also been noticed in which there is an 

 absolute coincidence in time between the occurrence of some 

 striking phenomena in the sun and a marked outbreak of magnetic 

 phenomena on the earth. A very interesting instance of this is 

 recorded by the distinguished American astronomer, Prof Young, 

 who, on the 3rd of August, 1872, perceived a violent disturbance 

 of the sun's surface. He was told the same day by a gentleman 

 who. was engaged in magnetic observations, and who was quite in 

 ignorance of what Prof. Young had seen, that he had been obliged 

 to desist from his work in consequence of the violent fluctuations 

 of the needle. On the same day a magnetic storm was indicated 

 by the instruments in England, at a distance of many thousand 

 miles from where Prof Young was making his observation. 



