222 



Dr. C. Chree. On the Relationships 



[Dec. 18 



least of the twenty-four hourly values in the mean diurnal inequality 

 for the month in question, based on the five quiet days selected for the 

 month by the Astronomer Eoyal, Calling this quantity R for any 

 particular magnetic element, I tentatively assumed 



R = a + 5S (1), 



with a and b constants. I grouped together the 11 Januarys, the 11 

 Februarys, and so on, of the 11-year period, and determined a and b 

 by least squares for each of the resulting 12 groups. There being- 

 only 11 years' data, the calculated values doubtless are appreciably 

 affected by quasi-accidental irregularities, but there is so striking a 

 resemblance between the more conspicuous features of the results 

 found for the declination, inclination and horizontal force as to 

 justify the conclusion that the phenomena are bond fide. Full parti- 

 culars will be given later. At present it will suffice to record the mean 

 values found for the a and b of the formula for three groups of months 

 ■ — viz. : — 



Winter, comprising November to February, 



Equinox ,, March, April, September, October, and 



Summer „ May to August. 



The results are as follows : — 



Table I. 



Horizontal force. Vertical force. 

 (Unit ly = 10 " 5 (Unit ly = 10~ 5 



Declination. 



Inclination. 



C.G.S.) 



C.G-.S.) 



Winter . . . 

 Equinox . . 

 Summer . . 

 Mean 



3' -23 



7 -32 



8 -91 

 6 -49 



b. 



0' -0323 

 -0478 

 -0428 

 -0410 



a. 

 0'*63 

 1 -26 

 1 -61 

 1-17 



b. 



0' -0105 

 -0147 

 -0137 

 -0130 



a. 

 10-5 

 23-5 

 306 

 21-5 



b. 

 0-161 

 -221 

 0-190 

 0-191 



7*0 

 17-2 

 22 -7 

 15 -6 



b. 

 0-032 

 026 

 0-035 

 0-031 



As is obvious from (1), a represents the amplitude of the range 

 corresponding to a total absence of sun-spots. During the eleven 

 years dealt with, Wolfer's mean monthly values for S varied from 0*3 

 to 129-2, the mean being 41*7. 



To bring out more clearly the similarity of the results for the 

 declination, inclination and horizontal force, I have represented the 

 mean value of b for the 12 months in each element by 100. The corre- 

 sponding values for the three seasons are, then, as follows : — 



Table II. 



Winter. Equinox. Summer. 



Declination 79 117 104 



Inclination 81 113 106 



Horizontal force 85 116 99 



