332" YOUNG'S WORK. [CHAP. 



called by us lines of that chemical element, are absent from 

 this part of the solar record. I show elsewhere that many 

 of the bright lines seen in prominences are very probably 

 lines due to descending cooler vapours, but even if we make 

 allowance for this the divergences observed by Professor Young 

 must still be regarded as extraordinary. 



To show this in connection with Professor Young's Sherman 

 observations of prominences ; in 1879 I prepared maps of the 

 spectra of calcium, barium, iron, and manganese. In these 

 the lengths of the lines in the spectra of the metallic elements 

 represent the intensities given by Thalen, whose lines and 

 wave-lengths I have followed in all cases, while those of the 

 lines visible in prominences, represent the number of times 

 each line has been seen in the spectrum of the chromosphere 

 by Professor Young. An inspection of these maps is sufficient 

 to show that there is no connection whatever beyond that of 

 wave-length between the spectra ; it will be gathered from 

 them how the long lines seen in our laboratories are sup- 

 pressed and the feeble lines exalted in the spectrum of the 

 chromosphere. 



Of these spectrum maps I give only that of iron, although 

 if space had permitted I should have been glad to add those 

 of calcium and barium, because in some cases the changes 

 of intensity in those spectra are even more striking than in 

 iron. 



2. Some Details of the Changes of Intensity in the Iron 

 Spectrum. 



In studying the iron spectrum we may not only consider the 

 visible portion, but we can also include in our inquiry that 

 recorded on my photographic plates, between H and G. 



It may be described as a very complicated spectrum, so far 

 as the number of lines is concerned, in comparison with such 



