134 BAUER— SOLAR ACTIVITY AND [April 23, 



tory for the period May, 1906, to January, 1909, and the variations 

 in terrestrial magnetic activity during the same period, as based 

 upon the observations at the five magnetic observatories of the U. S. 

 Coast and Geodetic Survey. Probably the most important result 

 then derived was that, in general, the earth's magnetization suffers a 

 diminution during a period of intense solar activity. This pointed to 

 the fact that the general, or average effect, of a magnetic storm was 

 to superimpose on the earth's magnetization a system of magnetic 

 forces equivalent to a demagnetizing system whose magnetic axis 

 was reversed from that of the earth's magnetic field, so that the 

 magnetic north pole of the disturbance system would lie in the 

 southern hemisphere. While this relation between changes in solar 

 activity and those in the earth's magnetism held, in general, for the 

 period examined (May, 1906-January, 1909) there were some mani- 

 fest contradictions also, so that for these an increase in solar activity 

 corresponded to an increase in the earth's magnetization. These 

 same contradictions were found to hold generally if we replaced 

 Hale's measure of solar activity by the Wolfer curve of sun-spot 

 frequency. There was thus again revealed the difficulty of establish- 

 ing a relation which would link solar with magnetic phenomena in 

 such a definite way that one set might be predicted from the other. 

 Additional discoveries regarding terrestrial magnetic disturbances 

 may now be reported upon. A recent examination of the times of 

 beginning of magnetic disturbances, as recorded at observatories 

 over the entire globe, showed that, without doubt, magnetic storms 

 do not begin at absolutely the same instant of time, as heretofore 

 believed. Instead, they are found to progress over the earth in some 

 definite manner and at a measurable speed. For the abrupt dis- 

 turbances, which are usually comparatively minute in their effect on 

 the compass needle, a complete passage around the earth would 

 require from 3>^ to 4 minutes. For the bigger effects, or for the 

 larger magnetic storms, the differences of time between various 

 stations are such that if these larger effects also traveled around 

 the earth completely, it might take them a half hour or more. The 

 following main conclusions were drawn :- 



-Journal Terrestrial Magnetism and Atmospheric Electricity, Washington, 

 D. C, Vol. IS, No. I, March, 1910 (18 and 20). 



