312 Scientific Intelligence. 



magnetic pole, and where the conditions of day and night are so 

 different, is of great interest, but requires careful consideration 

 before it can be regarded as representing real auroral changes. 



The accompanying curves [here omitted] illustrate the relation 

 throughout a year between the positions of the earth's poles with 

 reference to the sun ; the positions of the sun's poles as regards 

 the earth ; the frequency of magnetic storms at Greenwich and 

 Paris ; and lastly, the frequency of the aurora as observed at 

 Edinburgh and at stations in Scandinavia below latitude 65° N. 

 The first two curves are those that have already been mentioned, 

 but plotted differently. They have here been so arranged that 

 the maxima points represent the epochs when each of the poles 

 is most inclined to the sun or earth as the case may be. Both 

 the magnetic and auroral curves represent four of the set of 

 curves which Mr. Ellis* has recently published. 



It need scarcely be pointed out that the low minima of the 

 auroral curves during the summer months are due in great part 

 to the shortnesss of the nights, and therefore to the restriction 

 of the time available for aurora observations. 



The coincidence in time between the epochs of the maxima of 

 the frequency of magnetic disturbances and aurorse, and those 

 of the greatest inclination towards the earth of the north and 

 south solar polar regions is clearly indicated. 



It is interesting to inquire in what way this yearly inequality 

 of terrestrial magnetic phenomena is influenced when the sun's 

 polar regions are, for different groups of years, in an undisturbed 

 and disturbed condition. 



It would be expected that the oscillation of more disturbed 

 solar polar regions towards and away from the earth would tend 

 to increase the difference between the frequency of magnetic dis- 

 turbance at the equinoxes and solstices, while this difference for 

 those years when the less disturbed solar polar regions are in 

 action should be somewhat reduced. That this is actually the 

 case is brought out by the figures which Mr. Ellis has given in 

 the publication of which mention has already been made. 



Since the greatest magnetic storms are closely associated in 

 point of time with prominence disturbances in the polar regions 

 of the sun, to make the necessary comparison, therefore, the years 

 in which "great" magnetic storms occurred should be grouped 

 together and the yearly inequality determined, and another group 

 of years in which " great " magnetic storms were less frequent 

 formed and the yearly inequality also determined. Fortunately 

 a computation already made can be utilized for this comparison, 

 for Mr. Ellis has determined the number of days of greater fre- 

 quency (near sunspot maximum), and lesser frequency (near sun- 

 spot minimum), of magnetic disturbance, both groups practically 

 including the conditions required. Thus he has formed groups 

 of the years 1848-51, 1858-61, 1869-72, 1882-85, 1892-95, which 

 include, at any rate for the last three groups, the years where 



* Monthly Notices, R.A.S., vol. lxiv, p. 229. 



