Progress and Problems of Solar Physics. 135 



The Corona was of the typical form due to a qui- 

 escent condition of the solar surface, — extended 

 equatorial extensions, — instead of the radiated structure 

 which belongs to the sunspot maximum period. This 

 feature of the relationship of coronal type to the devel- 

 opment of solar spots was first suggested in 1878 by 

 Hansky, and the form of each succeeding eclipse had so 

 fully confirmed his discovery that in 1896 he forecasted 

 the general appearance of the corona of 1900, which in 

 the main proved to be verified. The question of coronal 

 modifications due to chromospheric eruptions, first 

 noticed by Belopolsky in 1897, has received confirmation 

 in later eclipses, that of 1901 disclosing to Professor 

 Perrine, of the Lick observatory, a violent coronal dis- 

 turbance issuing from the vicinity of a small bright 

 prominence. 



The spectrum of the corona appears to possess a 

 triple origin: a continuous spectrum, both original and 

 refiected, and a gaseous of bright line emissions; these 

 vary at times, the discontinuous being feeble, especially 

 near the sunspot minimum epoch. About a dozen 

 coronal lines have been observed with the spectroscope. 

 The fundamental gTeen ray designated as the '^Coronium 

 line" was traced to a distance of 325,000 miles in the 

 corona during the eclipse of 1889 by Keeler, but it is still 

 of an unknown substance. The original continuous 

 spectrum appears to emanate from incandescent solid 

 or liquid particles from the interior corona, and seem to 

 be of a phosphorescent nature, with little or no thermal 

 radiations. The reflected continuous spectrum is slight, 

 but clearly present at times, and mainly in the remoter 

 portions of the corona, Perrine having found thirty-five 

 Fraunhofer lines in his study of the photographic results 

 of the eclipse of 1901. This reflected light is probably 

 due to dust or fog according to Young, or some matter 

 which reflects sunlight; polariscopic observations also 

 confirm the presence of reflected light. 



Interesting speculations as to the nature of the 

 corona still occupy the attention of solar physicists; 

 that it is a true solar appendage and not an optical 

 phenomenon, as formerly supposed, is now proved. 



