406 SEE— THE NEW THEORY OF EARTHQUAKES [November 15, 



face sensibly affect the magnetic needle in the neighboring region. 

 This conspicuous effect would not be likely to arise if the magne- 

 tism depended on the whole earth, rather than on the crust, and 

 hence it seems to indicate that the seat of the earth's magnetism is 

 essentially shallow. Not only may we attribute the permanent mag- 

 netism to the crust, but we may also affirm that the upheavals of 

 the crust which have produced mountains have given rise to varia- 

 tions of the local field. 



Just how this arises may not be affirmed with entire certainty; 

 but the fact that disturbances have been noted during earthquakes 

 would seem to indicate bodily movement of magnetic matter, or 

 ordinary matter temporarily rendered magnetic. 



The outburst at Mt. Pelee, May 8, 1902, which instantly dis- 

 turbed the magnetic needle over a wide area, was probably due to 

 the ejection of a great mass of burning vapor high into the air, 

 which thus gave rise to such electric energy that the earth's mag- 

 netic field was suddenly disturbed. 



The eruption at Krakatoa produced a very similar effect, the 

 sudden development of an atmospheric charge vastly exceeding that 

 due to the greatest hurricane. (Report of the Krakatoa Com- 

 mittee, Royal Society, 1887.) A hurricane develops gradually and 

 the effect is scattered over a wide area; a volcanic outburst is 

 sudden and so concentrated that a considerable disturbance of the 

 earth's magnetic field may easily result. It is somewhat analogous 

 to the aurora borealis, but the location and cause is different and 

 the effect may be less rapid. In the aurora there is a discharge 

 between the upper and lower regions of the atmosphere, and this 

 redistribution of the magnetic tension in the earth's atmospheric 

 system causes a fluctuation of the magnetic needle, or a so-called 

 magnetic storm. 



Now in the case of a violent volcanic outbreak there is a similar 

 disturbance, owing to the sudden injection of a highly electrified 

 charge into the lower parts of the atmosphere, and the exchange 

 with the upper region continues for some time. Also when great 

 earthquakes occur there is violent shaking of a considerable region 

 of the earth's crust, and consequently some temporary, and per- 

 haps permanent, derangement of the elements of magnetism, owing 



