268 SCIENCE PROGRESS. 



Although the general distribution and intensities of the 

 lines in the gases from broggerite and cleveite sufficiently 

 corresponded with some of the chief " unknown lines " in 

 the solar chromosphere and some of the stars to render 

 identity probable, it was necessary to see how far the con- 

 clusion was sustained by detailed investigations of the 

 wave-lengths of the various lines. 



EMPLOYMENT OF HIGH DISPERSION. 



This was practically a separate branch of the work, as 

 the observations had to be made in the observatory. Next 

 I give here the observations relating- to D 3 , 4471. 



The Orange Line, A 5875*9. — Immediately on receiving 

 from Professor Ramsay, on 28th March, a small bulb of the 

 gas obtained from cleveite, a provisional determination of 

 wave-length was made by Mr. Fowler and myself, in the 

 absence of the sun, by micrometric comparisons with the D 

 lines of sodium, the resulting wave-length being 5876*07 

 on Rowland's scale. It was at once apparent, therefore, 

 that the gas line was not far removed from the chromo- 

 spheric D 3 , the wave-length of which is given by Rowland 



as 5875'98. 



The bulb being too much blackened by sparking to give 

 sufficient luminosity for further measurements, I set about 

 preparing some of the gas for myself by heating broggerite 

 in vacuo, in the manner I have already described. A new 

 measurement was thus secured on 30th March, with a 

 spectroscope having a dense Jena glass prism of 6o° ; this 

 gave the wave-length 5876*0. 



On 5th April, I attempted to make a direct comparison 

 with the chromospheric line, but though the lines were 

 shown to be excessively near to each other, the observa- 

 tions were not regarded as final. 



Professor Ramsay having been kind enough to furnish 

 me, on 1st May, with a vacuum tube which showed the 

 orange line very brilliantly, a further comparison with the 

 chromosphere was made on 4th May. The observations 

 were made by Mr. Fowler, in the third order spectrum of 

 a grating having 14,438 lines to the inch, and the observing 



