( 282 ) 



many wliirls. notwitlistandinfi' the Sun's I'Otation, may remain visible 

 tbi- a lonu' liiiit', allliongii contiimally clianuinu' its form, for we 

 really look alonu- a suecession of oliici- axes of whirls. The experiment 

 described above, may serve lo illustrate the fact that whirls, situated 

 in snrtaees of discontinuity which are not j)rojeeted in very narrow 

 bands, will /lot be seen as (Hstiiict spots. This is e. <>•. the case with 

 whirls, formed al ni(»rc than 'M) helio,ü-ra|»hic latitude. Near the 

 eqnatoi' also spots arc i-arcly seen : but this follows, accordinji' to 

 Emdkn's theory, from the circumstance that in those reiiions there 

 is less cause for the formation of whirls. 



To resume, spots will be seen in those parts where the distri- 

 bution of matter is such as to cause an abnormal iiiciwasc in the 

 divergent'y of the beams of light on tlieii* way to the Karth. As a 

 matter of course, there must al>o i»e parts where the distribution of 

 density causes a ih^crrasi' in dixergency and these are the places 

 Avhere fuciihii' are seen. < )ii a >uialler scale we lind the same con- 

 trast ill the so-called "pores and ,ui-amdation>"" of the photosphere. 

 All tlii'se solar phenonema are subject to rapid changes, because the 

 complicated optical system through which the rays of light reach us, 

 coiitiuiially allele its position with respect to the Earth. 



Till' ncr/oil/Cifi/ nf till' s/n/-sp(ifs. We w ill now endea\uui' iu [)ro\e 

 that ill onh'r to explain the 11-year pcM-iod in the fre((nency, the 

 total s[>otted area and the mean heliographic latitude of the suii->pots, 

 we need not admit tiie hypothesis of a |»eriodical chaiiu'c in the Siin"s 

 "acti\'ity'". 



Let us for a moment sup))ose that all actual changes in the hirin 

 of the Sun suddenly came to a stand-still, but that its rotation con- 

 tinued : even flini an .r-year period would be observable in the 

 Sun's appeai-ance, the i)Osition of spots and taeniae etc., because each 

 time, after .r years have elapsed, the point /-* follows again nearly 

 the same path. 



However, the real conliguration of the Sun is j/ot [lerfectly con- 

 stant (although probably its change is \ery slow and gradual) 

 and so we may consider the 11-year period to be the result of the 

 joint action of a contuiuous (perhaps somewhat irregular but not 

 necessarily pei'iodical) clini/i/i' in the Sirns >nii'/<(ces of c/Lsco7itimiift/, 

 together w ith tlw j):'rio'/ic'iI rariation hi tin' jiosition of the Enrth 

 ir'tth. /-('sprrf to the ''arerrujc rotdt'nKj sini'\ 



We define the meaning of this latter expression Ity our sphere 7i, 

 whose synodical period of revolution coincides with the i)eriod of 

 circa 26 da\ s, which has been noted in tcrre.strial phenomena. 



