A NEW METHOD OE RESEARCH. 9 



This method, when tried by the writer at the Harvard Observatory 

 in 1890, proved unsuccessful. The lack of success was partly due to 

 the fact that a line of hydrogen was employed. This line, though 

 fairly suitable for the photography of prominences with the perfected 

 spectroheliograph of the present day, was too faint for successful use 





Fig. 2. The Solar Chromosphere and Prominences. 



amidst the difficulties which surrounded the first experiments. Ac- 

 cordingly, when the work was resumed a year later at the Kenwood 

 Observatory in Chicago, an attempt was first made, through a photo- 

 graphic investigation of the violet and ultra-violet regions of the promi- 

 nence spectrum, to discover other lines better fitted for future experi- 

 ments. In the extreme violet region, in the midst of two broad dark 

 bands which form the most striking feature of the solar spectrum, two 

 bright lines (H and K) were found which were attributed to the vapor 

 of calcium. They had previously been seen visually in the promi- 

 nences, but on account of the insensitiveness of the eye for light of this 

 color, their true importance had hardly been realized. A careful study 

 soon showed them to be present in every prominence observed, at eleva- 



