III.] THE PRESENT POSITION. 33 



lines behave like those of a metal when a compound of a metal is 

 broken up by the action of heat. 



Each line of each element, at whatever temperature it is produced, 

 can at once be compared in relation to position in the spectrum with 

 the lines visible in celestial bodies with a view of determining whether 

 the element exists in them. 



At the time at which the earlier inquiries of this kind were made 

 it was only possible for the most part to deal with eye observations of 

 the heavenly bodies. The results were, therefore, limited to the visible 

 spectrum. 



During the last few years photographs of the spectra of the brighter 

 stars and of the sun's chromosphere during eclipses have been obtained ; 

 it became of importance, therefore, to extend the observations of terres- 

 trial spectra into the photographic regions for the purpose of making 

 the comparisons which were necessary for continuing the inquiry. 



The recent work has been done with this object in view. 



The way in which the enhanced lines have been used is as follows. 

 Those belonging to some of the chief metallic elements have been 

 brought together, and thus form what I have termed a " test-spectrum." 

 This has been treated as if it were the spectrum of an unknown element, 

 and it has been compared with the various spectra presented by the sun 

 and stars. 



How marvellous, how even magnificent, the results of this inquiry 

 have been, I shall show later in detail ; but I may here say by way of 

 anticipation that the test-spectrum turns out to be practically the 

 spectrum of the chromosphere, that is, the spectrum of the hottest 

 part of the sun that we can get at ; and that a star has been found in 

 which it exists almost alone, nearly all the lines of which had previously 

 been regarded as " unknown." 



This last result is of the highest order of importance, because it 

 should carry conviction home to many who were not satisfied with 

 the change of spectrum as seen in a laboratory, where always the 

 enhanced lines seen in the spectrum of the centre of the spark 

 have alongside them the lines in the spectrum of the outer envelope, 

 which of course is cooling, and in which the finer molecules should 

 reunite. For twenty years I have longed for an incandescent bottle in 

 which to store what the centre of the spark produces. The stars have 

 now provided it, as I shall show. 



Although I have promised to pass over the history of the work 

 generally, I must still point out that the enhanced lines in the test- 

 spectrum actually include all those first studied years ago when every- 

 thing was dim, and we were seeing through a glass darkly ; not as we 

 are now, face to face. To show the rigid connection of the new with 



D 



