( 271 ) 



o 



Hourly distribrution of the maximum (in 7o) 

 Hour '2 4 6 



noon 

 10 I'i U -1Ü 18 20 22 



Intensity 



'11.5 6.7 5.51.84.712.812.65.3 6.1 6.110.916.2 



2 I 10.9 9.1 5.91.21.4 7.3 7.63.9 7.610.813.515.2 



» 3 and 4 



All 



Intensity 



» 3 and 4 



11.2 4.0 2.41.60.8 4.0 7.26.812.013.617.219.2 



14.1 7.4 4.9 1^2.4 8.6 9_2 4^ 7.8 9.7 13.3 16.3 



12.3 1G_7 10.9 5.8 4_3 13^ 5.8 2.9 2_^ 5.110.1 9.4 



11.3 T? 3.6 5.6 3_3 8.5 11_^ 8.5 6.1 5.2 14.1 14.9 



12.2 9.3 5.8 3.2 3.5 7.7 9.0 6.4 8.0 7.7 10.3 17^ 



All 



11.9 10.2 6.04.63.6 9.2 9.26.5 6.3 6.311.614.8 



These hourly numbers show for each intensity, and for both kinds 

 of storms the same, strongly marked distribution over the hours of 

 the day. 



Thus the development of agitation during a storm is dependent 

 on the position of the sun relatively to the station in a manner 

 which is the same for S- and G-storms. 



The period has a principal maximum at lO"! p. m. and a secondary 

 one at noon; and being compared to the diurnal periodicity of the 

 commencement of G-storms, it is evident, that: On the hours when 

 the chance for a maxiinum-agitation begins to increase, ive may expect 

 most storms to. take a start. 



Hence we may come to the following supposition. 



The susceptibility of the earth's magnetic field to magnetic agitation 

 is liable to a diurnal and semidiurnal ijeriodicity. Whatever may be 

 the origin of the increase of agitation, sudden or gradual, this period' 

 icity remains the same. 



This was the same thing, that was revealed to me by the inspec- 

 tion of the hundreds of curves in preparing the list. 



The agitation rises at about S'^ a. m. after some hours of great 

 calm and reaches a maximum at about noon. A second period of 

 calm, less quiet however than in I he early moniing, is reached- in 

 the afternoon, and a second rise follows till a maximum is attained, 

 shortly before midnight. 



