DEPARTMENT OF TERRESTRIAL MAGNETISM.' 



Lofis A. Bauer, Director. 



GENERAL SUMMARY. 

 INTRODUCTORY REMARKS. 



The notable disturbances of the Earth's magnetism, brilliant polar- 

 light displays, and severe earth-currents of May 13 to 16, 1921, which 

 accompanied the remarkable sun-spot activity at the time, drew 

 renewed attention to the relationships between these four classes of 

 natural phenomena. The earth-currents generated within the Earth 

 during the period of disturbances were of such a nature and magnitude 

 as to cause on several days unusually serious interruption of tele- 

 graphic transmission, and disturbance of various other electric instal- 

 lations. In consequence, further information as to the precise causes 

 and modes of action of disturbances in the Earth's magnetic and 

 electric conditions is being zealously sought, both on theoretical and 

 on purely practical grounds. 



Telegraph companies have requested observers of sun-spots to keep 

 them informed of notable solar phenomena in the hope that they might 

 take whatever advance steps repeated experiences would show prac- 

 ticable for the prevention of serious interruptions from this source in 

 telegraphic transmission. So, likewise, these organizations and in- 

 terested persons are soliciting information regarding disturbances of 

 the electric currents continually flowing in the Earth's crust and re- 

 garding deflections of the compass needle and the Earth's magnetism 

 in general. Requests for such information are quite general. Thus, 

 for example, the Telegraphs Branch of the Commonwealth Postal 

 Department of Western Australia has requested of our observer-in- 

 charge at the Watheroo Magnetic Observatory that he keep it in- 

 formed of any abnormal magnetic conditions. 



The Earth's magnetic changes are being continually recorded at 

 about 50 stations, which, unfortunately, are not distributed over the 

 Earth with the desired uniformity; the great majority are in Europe 

 and only about 20 per cent are located in the Southern Hemisphere. 

 But matters are still worse as regards earth-currents, since they are 

 continuously recorded at less than 10 per cent of the total number of 

 magnetic observatories. On the North American continent, Hawaii 

 and Porto Rico, there are in operation 7 magnetic observatories, but at 

 none of these, owing to various reasons, are there installations for 

 earth-current observations. Accordingly, desired specific informa- 

 tion can not at present be supplied to our telegraph companies and 

 those interested in electric disturbances. 



'Address, Thirtj'-sixth Street and Broad Branch Road, Washington, D. C. 



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