( 278 ) 



occupied hv P in its helical course on the s|»liere. and we need only 

 admit that at snii-sjint iiKi.iimnm I he siptn-n/i' I'tii/s of (In' fahil licdiii 

 of li'lJit ri'dclilinj IIk' I'ldilli, (111(1 j'niiii irliidi /W /'s tJu' cciili'dl lliic^ 

 llKH'i' ofti'll jKlss fur (I citusuU'fithh' distdiici' vJosi'lif dh'tuj sii r faci'.'i 

 of (Uscoiittniiihi, tliiin In, tlnics of muiiiinini. If we admit this view, 

 then our ex|»lanati(»n of the spectral peculiarities reads thus: 



A iiiouochroiiialic Itcani of liuiii, passinu' on its way closely along 

 a surface of discontinuity, \vill underuo a marked clianue of di\ei-- 

 gency, when, for tlntse particular waves, the medium has a great 

 (positive or negative) refiaction constant. We may j-ather expect an 

 increase than a decrease of (he divergency, because the medium 

 becomes more rarefied with the increasing distance IVoni the Sun's 

 centre. As a rule such a iteam will reach the Earth with a lesser 

 intensity than the l)eams of i-ays which ujidergo less refraction. The 

 consequence is that, through the scattei-ing of neighbouring rays, all 

 FHAiNnoi'KH lines which cause anomalous dis|)('r>io)i will lia\e a 

 somewhat darkened background. Willi some lines this backgroinid 

 is broad (If, K, the lines of hydrogen, iron, in a woi-d, all the 

 well known wideiUMl lines of the solar spectrum): with others it is 

 nai'row : it (lepeixN on the proportion of these elements containe(l 

 in the solar atmosphere and on the sliajx' of the disjiei-sion cur\c ; 

 but at all events, the mean intensity o\er the entii'e sjiccti'um must 

 have become less, by the light ])assing along the surfaces of discon- 

 linuily. In \ears of sun-spol maxima this hap[)ens more often 

 than at minima, an<l this gives us the explanation of the results 

 olttained l>y Nokd.mann. ' ) 



It now remains for us to jtrove that the same cause, which in 

 the period of spot maximum makes weak lines in the spot spectrum 

 to appear strengthened, makes also strong lines to appear \\eakened. 



We again refer to oui- e.x|)Ianation of the abnormal spectrum of 

 Half,. At that time we supposed the structure of the corona to be 

 "tubular". Later considerations have induced us lo define the structure 

 of the exterior p.irts of the Sun as i-ather "lamellar", a correction 



1) The kinds of rays whicli by dispersion have disappeared fcüai the sunliglil 

 visible to us, travel to other parts of the universe, lar from the orbits of tlie 

 planets, wliere lliey would be seen as faculae, chroniospliere light and corona 

 light. It" it were possible, by means of the spectroscope there lo study the mean 

 radiation, we should find in the continuous spectrum some bright lines, lying on 

 both sides of the real absorption lines and in close proximity to them. Some stars 

 present this phenomenon. It may, ttierefore, be explained by the assumption that 

 tliey are bodies resembling llie Sun, l)ul lliat our line of siglit forms a ralher 

 large angle with their fqiialor. 



