40 
DR. S. CHAPMAN ON THE SOLAR AND LUNAR 
seasonal harmonics (of. Table I). The differences are in most cases easily within the 
limits of accidental error. 
As regards the lunar diurnal magnetic variation, the corresponding value of S/ti is 
121, and, as Table K shows, the above values of a would hardly be affected by the 
change. The calculated values for the lunar variation are given in Table J, alongside 
the observed data. Considering the uncertainties in the determination of the small 
quantities concerned, the agreement between the two sets of values is good. The 
observed phase differences are, with one exception, of the right sign, and their mean 
( — 20 ’6) is in satisfactory accordance with the mean value of a ( — 19°'0). The lunar 
variation, therefore, supports the above hypothesis as fully as the reliability of the 
data allows one to expect. 
The theoretical values of f corresponding to the values of a in Table M were then 
compared with the observed amplitude-ratios (which we denote by f), and in 
accordance with (23), the values of (f'/f ) 1/2m+1 , or R/R tf , were calculated for each of 
the annual harmonics Q„" +1 . The four values found were 
(23a) 1'068, D030, D041, D041 (R/R c ). 
Adopting the value 1 '04, the following calculated values o if were deduced from 
the formula 
(24) = (l'04) s " + ‘/«.,,c. 
both for the annual and seasonal harmonics : — 
Table N.—Amplitude Ratios of the Surface Potentials of the External and Internal 
Diurnal Magnetic Variation Fields. 
Annual harmonics. 
Seasonal harmonics. 
— 
J calc* 
/'• 
— 
dcalc* 
Calculated. 
Observed. 
Calculated. 
Observed. 
Qd 
2-05 
2-49 
2-8 
Q1 1 
2-42 
2-72 
2-3 
Qa 2 
1-83 
2-41 
2-2 
Q2 2 
1-88 
2 • 29 
2-45 
Qd 
1-74 
2-47 
2-5 
Qs 3 
1-73 
2-27 
2-1 
Q5 4 
D70 
. 
2-61 
2-7 
Qr 4 
1-67 
2-37 
1-7 
Mean .... 
2-50 
2*55 
Mean .... 
2 • 41 
2-14 
Again the agreement with observation must be considered satisfactory, so that 
with the aid of only two disposable constants (p and R c /R) a good account has been 
