178 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 2 



ability" of geomagnetism at any one X)lace — changes, on the one hand, 

 slow when compared with the life span of the individual, as in its 

 long-time or secular change, and, on the other hand, rapid, as in its 

 short-time or more ephemeral changes ; it is largely in the latter that 

 we find interrelations with cosmical phenomena in space about us. 



The compass appears simple though mysterious in its directive 

 ability which demonstrates that magnetic forces are present every- 

 where about us. This is evidenced also by the inductive magnetic 

 action of the earth's field upon a material highly susceptible to such 

 action, for example, an alloy such as permalloy with unusually great 

 capacity for transient induced magnetization in weak magnetic 

 fields like that of our planet. When a thin* long rod of permalloy 



I IGUBE 1. — Sunspot numbers and cycles of plus and minus polarities, 1900-1940. 



(After S. Ij. Nicholson.) 



is directed toward the north magnetic pole of the earth, the mag- 

 netization induced in the bar by the geomagnetic field is quite suffi- 

 cient to lift small pieces of permalloy. But as the rod is turned with 

 its length at right angles to the field and thus in the direction least 

 favorable to induction, it loses the magnetism induced by the earth 

 and will no longer support such metal strips, which fall. But that 

 which is apparently simple is often the most baffling as in this case, 

 perhaps not in the physical principles concerned, yet certainly in the 

 origin and observed periodic and aperiodic fluctuations of the, forces 

 involved. 



The first perception of the natural phenomena of geomagnetism 

 through the directive property of a lodes tone or magnet freely sus- 

 pended in the earth's field is veiled by the myths and legends of 

 south-pointing chariots in China some 4,500 years ago and of its ap- 

 plications by the Egyptians, the Phoenicians, the Greeks, and the 

 Tiatins. However, there is definite and well-authenticated evidence 



