I9I0.] TERRESTRIAL MAGNETIC DISTURBANCES. 131 



less interesting, and possibly equally important to that mentioned — 

 the investigation of the causes of those mysterious influences which 

 daily, hourly, year in and year out, impress themselves upon the 

 earth's magnetism. It is confidently believed by many that we must 

 look primarily to the fluctuations of the delicately poised and sensi- 

 tive magnetic needle for the key which will unlock the door to knowl- 

 edge of the mysterious forces, coming from the regions beyond and 

 conditioning the phenomena on which our welfare and development 

 may, in no small measure, depend. 



But aside from any such possible practical results, the belief is 

 not without foundation that just as the great doctrine of evolution 

 resulted from the persistent and searching inquiry into the causes 

 producing the variations and mutations in biological phenomena, 

 our knozvledge of the earth's magnetism is primorily to he advanced 

 throngh the study of zvhat causes the earth's magnetism to vary. It 

 also appears that when we shall have made an exhaustive study of 

 the periodic magnetic variations, such as the solar-diurnal, the lunar- 

 diurnal, the annual, etc., we shall find that none of these is strictly 

 cyclic, but that each runs its course, through periods incommensur- 

 able with one another, the resulting residual effects at any moment 

 of time being of sufficient magnitude to be reckoned with. Thus it 

 may be possible to account for the secular variation of the earth's 

 magnetism without resorting to any other cause than those daily in 

 operation. 



I shall now give a sketch of the chief results obtained along a 

 line of inquiry being conducted cooperatively between two depart- 

 ments of the Carnegie Institution of Washington — the Solar Obser- 

 vatory at Mt. Wilson, California, under the direction of Professor 

 George E. Hale and the Department of Research in Terrestrial 

 Magnetism — viz., as to the connection betzveen solar actiznty and the 

 earth's so-called magnetic storms. 



At an instant, without any previous warning, magnetic needles 

 are caused to swing out of their usual position or direction, earth 

 electric currents are generated of sufficient strength to interfere with 

 telegraph and cable lines, brilliant and wide-spread auroras are 

 evoked, and even electric car line traffic is momentarily suspended — 

 by what? That is the problem. Possibly at the same time there 



