TERRESTRIAL MAGNETISM HAZARD 251 



mathematically and concluded that any effect due to rotation would 

 be too small to be detected. In 1900 Sutherland sugf^ested as a pos- 

 sible cause of the earth's magnetism the rotation of an electrostatic 

 field within the earth (a positively charged core and a negatively 

 charged crust, or vice versa), as Rowland's experiments had proved 

 that a moving charge of electricity produces a magnetic field analo- 

 gous to that of a current, but this theory proved untenable when sub- 

 mitted to analysis. 



The development of the electronic theory of matter with the atoms 

 consisting of a positively charged nucleus surrounded by negatively 

 charged electrons led Sutherland to suggest that if for some unknown 

 reason connected with gravitation the negative charge of the atom 

 was further from the center of the earth than the positive charge by 

 only 0.4X10"^ cm., it would account for a magnetic field comparable 

 with that of the earth. Here again, when the theory was sub- 

 mitted to analysis and the electronic theory was more fullj^ de- 

 veloped, it was seen that Sutherland's hypothesis was untenable 

 either qualitatively or quantitatively. 



Failing to find a satisfactory explanation of the earth's magnetism 

 on the basis of the known properties of matter and the accepted 

 laws of electrodynamics, J. J. Thomson, Sutherland, Bauer, and 

 Swann have suggested that we may have to look for some slight but 

 fundamental modification of those accepted laws, possibly as re- 

 gards the mutual attraction and repulsion of moving positive and 

 negative electrons, similar to a suggestion by H. A. Lorenz regard- 

 ing the cause of gravitation. Indeed there seems to be growing a 

 belief that gravitation and terrestrial magnetism are very closely 

 allied and probably to be traced to a common origin. 



Realizing the difTiculties in the way of a direct attack on the 

 problem, especially before more complete observational data were 

 available, many magneticians have turned their attention to a studv 

 of the variations of the earth's magnetism and their correlation with 

 associated phenomena, such as atmospheric electricity, earth cur- 

 rents, auroras, sun spots, solar radiation, meteorological phenomena, 

 hoping in this way to throw light on the main problem. In parti- 

 cular, magnetic storms, those irregular disturbances of large amp- 

 litude and comparatively short duration, have been the subject of 

 nuich study. 



From the time of the earliest comparisons of photographic records 

 from w^idely separated observatories, it was recognized that the more 

 severe magnetic disturbances occur at practically the same time all 

 over the earth, and further comparative study of abrupt beginnings 

 and sharp turning points indicated strict simultaneity, the depart- 

 ures therefrom being ascribed to errors inherent in the time measure- 

 ments, so that more accurate determination of the time of occurrence 

 of such salient features was suggested as a method of determining 



