CHAPTER XXIII. 



MOllE TESTS. THE SPECTRA OF SUN-SPOTS.' 



IN the last chapter when endeavouring to show how the new 

 hypothesis fits the facts better than the old one there were 

 some points on which I promised to give further information 

 depending upon later work. This I now proceed to do with 

 regard to those which refer to spot-spectra, or to the comparison 

 of such spectra with those of the prominences. 



The first attempt I made 1 to get light out of this inquiry 

 was one which dealt with a long catalogue of lines observed by 

 Professor Young in his memorable expedition to Mount Sherman, 

 where, at the height of between 8,000 and 9,000 feet, with per- 

 fect weather and admirable instrumental appliances, about a 

 month was employed in getting such a catalogue of lines as 

 had never been got before. But it was found that, although 

 the result of this inquiry was to strengthen the evidence in 

 favour of the inversions referred to at p. 175, still, after all, 

 one wanted more facts. In this changeable climate I soon 

 found that it would not do to proceed as I began to attempt 

 to observe all the lines acted upon in a solar spot. The excessive 

 complication, and the great variation of a spot-spectrum from 

 the ordinary solar spectrum, cannot be better shown than by 

 the accompanying copy of a spectrum of one of the sun-spots 

 observed at Greenwich. 



1 Proc. R. S. No. 197, 1879, page 251 and seq. 



