54- 



NA TURE 



\AprilZ, I? 56 



'4 When we go fmtiier afield into the outer corona we leave 

 behind us most of the bydvogen lines, but one, the green line F, 

 remains for a considerable height side by side with the 1474 line, 

 indicating, as far as we can see where everything is so doubtful, 

 that so far as the gaseous constituents of the outer corona are 

 concerned they consist most probably of hydrogen in a cool 

 form, and this unknown stuff which gives us the line 1474. 

 With regard to the other materials of the outer corona we 



17.— Diagn 



ults of the Italian observations foi 



that the spectrum of the limelight is continuous, but that it was 

 probably excessively complex in its origin. 



General Connection of the Foregoing Phenomena 

 We next come to an excessively important point — the connec- 

 tion of the various phenomena which we have now pa sed under 

 review with each other. 



The Italian observers have not only very carefully observed 

 the prominences from day to day, but they 

 have observed spots and the other pheno- 

 mena which require continuous investiga- 

 ition. The accompanying diagram puts 

 llogether in a very convenient form much 

 {information which we want at the present 

 moment. The information extends over 

 three years, so that we have not merely to 

 ilepend on the result of one year's observa- 

 tion. The curious-looking hieroglyphics, 

 wliich are called curves, have a very simple 

 explanation. In the middle of each of these 

 series E stands for the equator, and right 

 :ind left of that we have vertical lines giving 

 every 10° of latitude from the equator to the 

 |)o'es south or north for each year. The 

 lieight of the curves from the base-line re- 

 ]iresents the number either of spots, faculse, 

 metallic or quiet protuberances seen each 

 year. The spots in the year iSSi had their 

 maximum in latitude 20° N. and 12° S. 

 'fliere were no spots either nortli or south 

 t)f latitude 40°, and there were very few 

 lie -ears i88i-8i spots indeed near the equator of the sun. 



10 je a I I- 3. j^ \%^i the conditions are a little changed. 



There are some spots near the equator, and 

 the maxiuaum of spots now is 18° N., and there are more 

 spots this year than there were last, because the curve is 

 higher. Going on to 1S83 the maximum of spots has changed 

 from the north of the equator to the south, and in latitude 15° S. 

 reduced maximum, whereas in the northern hemi- 



know that it contains particles which reflect the ordinary sun- 



liglit to us, because in 1871 Dr. Janssen and in 1878 Prof 



Barker and others saw the dark Fraunhofer lines in the spectrum 



of the corona. \\'e must imagine, therefore, that some part of 



the s]>ectrum of tlte corona' depends for its existence on solid we have 



particles which not only give us such a spectnim as the limelight sphere we get very nearly the same quantity in latitude-; 10° and 



does, but which further have the faculty of reflecting to us the 20". The other curves may now be compared with these, and the 



light of the underlying photosphere. point of enormous importance is this, that the maxima factdse 



and the metallic prominences agree 

 absolutely in position with those of 

 the spots. 



When and where the spots are 

 at the maximum the faculre and the 

 metallic prominences are at the 

 maximum. If the maximum changes 

 from north to south, as it does, in 

 the spots, it changes from north to 

 south in the metallic prominences, 

 and from north to south in the 

 facukis ; so that were we dependent 

 on these diagrams alone, represent- 

 ing three years' work, we should be 

 ilriven to the conclusion that there 

 is absolutely tlie most tremendous 

 and important connection between 

 spots, the metallic prominences, and 

 the faculre ; and not only that, we 

 reach finally the fact of the wonder- 

 ful localisation of these phenoinena 

 upon the sun. The spots are never 

 seen north or south of 40°. They 

 are invariably seen in smaller quan- 

 tity at the equator ; similarly the 

 facula: do not go very much further 

 than 40' north or south, and their 

 minimum is also at the equator. 

 The metallic prominences also 

 never go very much beyond the 

 also have a minimum at the 



Fig. 18.— Spo 



e indicates the amount of spotted i 

 1 latitudes of the spots. 



It was also put beyond all question in the eclipse of 1882 in 

 Egypt that this corona has another sp"ctrum of its own. I was 

 fortunate enough to see that eclipse under very good conditions, 

 and the spectrum which had been supposed up to that time to 

 be a continuous spectrum only was an integration of a consider- 

 able number of spectra. T here were bright bands and dark 

 bands from one end of the spectrum to the other, showing that, 

 with these additions, it was no longer continuous in the same way 



and they 



spot region, 

 equator. 



But when we pass to the protuberances of the quiet sort that is 

 not so. They extend from one pole of the sun to the other, so 

 that whatever it may lead us to, we are bound to consider that 

 there is the most intimate connection between spots, metallic 

 prominences, and facuke, and that there is a great difference 

 between the metallic prominences and the quiet ones. 



That 



