90 



Sir Norman Lockyer and Dr. W. J. S. Lockyer. [June 3, 



A Probable Cause of the Yearly Variation of Magnetic Storms 

 and Aurora." By Sir NORMAN LOCKYER, K.C.B., LL.D., 

 F.R.S., and WILLIAM J. S. LOCKYER, M.A. (Camb.), Ph.D. 

 (Gott), F.B.A.S., Chief Assistant Solar Physics Observatory. 

 Received June 3, Read June 16, 1904. 



The ordinary meteorological elements, such as atmospheric pressure, 

 temperature, etc., have a yearly change satisfactorily explained as due 

 to changes of the position of the earth's axis in relation to the sun, or, 

 in other words, the variation of the sun's declination. There are, 

 however, other phenomena, such as magnetic disturbances and aurora, 

 which have been explained differently. 



Thus, in regard to this seasonal variation Mr. Ellis* has written, 

 " The related physical circumstance is that at the equinoxes, when 

 disturbance is more frequent, the whole surface of the earth comes 

 under the influence of the sun, whilst at the solstices, when magnetic 

 disturbance is less frequent, a portion of the surface remains for a 

 considerable period in shadow." 



The object of the present communication is to put forward another 

 possible cause. 



It has been previously pointed outf that a very close relationship 

 exists between the epochs of occurrence of prominences in the polar 

 regions of the sun and Ellis's " great " magnetic disturbances. This 

 synchronism showed that either the polar prominences themselves, or 

 the disturbances thus indicated in these polar regions, were the origin 

 of these "great" magnetic storms, or that they were caused by a 

 more general stirring-up of a greater extent in latitude of the solar 

 atmosphere. 



A further investigation J indicated, however, that in all probability 

 it was either the actual polar prominences themselves, or the activity 

 in the solar polar regions, that initiated these magnetic disturbances, 

 for it was there pointed out that the presence of polar prominence 

 activity-tracks synchronised with the appearances of large "polar" 

 coronal streamers. Here we have an indication of a local cause and 

 effect. 



(t will be gathered, then, that, even as regards terrestrial magnetic 

 phenomena, considerable importance must be attached to action taking 

 place in the regions about the solar poles. 



Since the axis on which the sun rotates is inclined to the plane of 

 the ecliptic, there will be times throughout the course of a year when 



ir polar regions will be exposed most and least to the earth. 

 4 Monthly Notices,' vol. 61, p. 540. 



Roy.Soc. Proc.,'Tol. 71, p. 244; also 'Monthly Notices, B.A.S.,' vol. 63, 

 Appendix I, p. 6. 



J ' Monthly Notice*, R.A.S.,' vol. 63, p. 481. 



