( 295 ) 



In tlio values of h flic periodicitv A plavs a far ,i>i-calci- part tlian 

 ill those of (I. That stands to reason; lur tiie lei'iu InS less eoiicefiis 

 th(> anioujil of the ueiiei-al atmospheric cireuhxtion, tliaii it does the 

 |)e(*uiiai'iti(»s of the siirfaec^s of diseoiitiiiiiil v in resi»ecl h» ihe Knrlh. 



In Ihe \alnes of the vertical intensity, A, as eonipai'ed to ^/, lias a far 

 lesser siuiiilieanee than in those (»f !he olher three elements. (!iiHKK 

 mak(^s the mean \alne of A oxer a whole year 100 and then iirrixes 

 at the following' \aliies of h for Ihe seasons. 



Declination Inclination lloriz. ijit. 

 Winter 79 81 85 



Spring and an In nm 117 J13 lJ(i 



Snm]ner 104 10() 99 



Thns it a[>pears that the anijjlilnde of the dinrnal ineipialily, taken 

 absolutely, depends in a far inreater measure on snn-sj)ot frequency 

 at the times of the e(juino.\es than al other limes. The I'eason of Ihis 

 we find in the fact that the greater variety of shar|)ly delined planes 

 of discontinuity which at spot maxima intersect the Earth, causes 

 greater diversity in ils illumination when the in'ojection of the diurnal 

 motion on the normals to the jtlanes is lai'ge, than when il is small. 

 (Compare Fig. 2 p. 289). 



Now, if we consider the inlluence of Ihe spot frecpiency notahs(t- 



lutely, l)ut in comparison with Ihe inlluence of the annual xariation 



taken for arei-ajji' spot frequency, a relative value which C^hkee 



4,1 7/> 



expresses by the quotient , then we obtain : 



a 



Declination 

 Winter 0.42 



Spring and antumn 0.27 

 Summer 0.20 



which shows that the influence of the s|)ot frequency on the ampli- 

 tude of the daily inecpiality is coiiiixiratu-ehj strongest in winter. This 

 must be attributed to the fact that during a winter day the changes of 

 position of a point on the globe with i'es|)ect to the Sun and to the 

 surfaces of discontinuilx are |»ro|)orlionally small, and conseipiently 

 Ihe variations in illumination are then principally caused by irregular- 

 ities, occurring in the system of tlu^ planes of disconlimnly ilself 



The investigations of ('iirkk were confined lo Ihe observations at 

 Kkw. \ synopsis of the annual xariations in the daily inequality of 



20* 



