Solar Changes of Temperature and Variations in Rainfall. 415 



latitude as the spots. This is especially well shown by the diagrams 

 illustrating the distribution of spots, faculse, eruptions, and protube- 

 rances which are given by Tacchini for 1881 1887 in the ' Memorie 

 della Soc. degli Spettroscopisti Italiani,' 1882 1888. These curves 

 show in the most unmistakable manner that the spots, faculse, and 

 eruptive or metallic prominences have their maximum frequency in 

 the same solar latitudes while the nebulous or quiet prominences are 

 more uniformly distributed, and even have maxima in zones where 

 spots are rarely observed. This is corroborated by what Professor 

 Respighi many years ago stated : 



" In correspondence with the maximum of spots, not only does the 

 number of the large protuberances increase, but more than this their 

 distribution over the solar surface is radically modified." 



In his observations, Professor Young found that the H and K lines 

 of calcium were reversed in the chromosphere as constantly as h or C, 

 and the same lines " were also found to be regularly reversed upon the 

 body of the sun itself, in the penumbra and immediate neighbourhood 

 of every important spot."* This result was confirmed by the early 

 (1881) attempts of one of us to photograph the spectra of the chromo- 

 sphere and spots, and also by eclipse photographs. In the photographic 

 spectrum, the H and K lines are by far the brightest of the chromo- 

 spheric lines, and this fact has been utilised by Hale and Deslandres, 

 acting on a suggestion due to Janssen, for the purpose of photo- 

 graphing at one exposure the chromosphere and prominences, as well 

 as the disc of the sun itself, in the light of the K line. 



These photographs thus give us in K light the phenomena which one 

 of us first observed by the lines C and F of hydrogen, and thereby 

 I present a record of the prominences across the whole disc of the sun 

 as well as at the limb. 



In such photographs near sunspot maximum, the concentration of 

 the prominences in zones parallel to the equator is perfectly obvious at 

 a glance. Eruptive or metallic prominences are thus seen to cover a 

 much larger area than the spots, so that we have the maximum of solar 

 activity indicated, not only by the increased absorption phenomena 

 indicated by the greater number of the spots, but by the much greater 

 radiation phenomena of the metallic prominences ; and there seems 

 little doubt that in the future the measure of the change in the amount 

 of solar energy will be determined by the amount and locus of the 

 prominence area. 



Spots are, therefore, indications of excess of heat, and not of its 

 defect, as was suggested when the term " screen " was used for them. 

 We know now that the spots at maximum are really full of highly 

 heated vapours produced by the prominences, which are most numerous 

 when the solar atmosphere is most disturbed. 



* ' Catalogue of Bright Lines in the Spectrum of the Chromosphere/ 1872. 



