1879.] On the unknown Chromo spheric Substci7ice of Young. 475 



the line wave-length 5535 readily reversed, while that with wave- 

 length 5518 is less easily reversed ; the line wave-length 4933 is 

 comparatively easily reversed, whereas that with wave-length 4899 

 has not been reversed by us. On the other hand, the line wave-length 

 4553 has been reversed, but not the line wave-length 4524. In the 

 case of strontium, the lines wave-length 4831 and 4812 have been 

 reversed, but not the line wave-length 4784, and the two lines wave- 

 length 4741 and 4721 remain both unreversed. In the group of five 

 lines of calcium, wave-length 4318 to 4282, it is only the middle 

 line wave-length 4302 which has been reversed. Of the potassium 

 groups of lines wave-length 5831 and 5782, 5802, 5782 are reversed, 

 the line wave-length 5811 has not been reversed, and of the others the 

 line wave-length 5802 is the first to appear reversed. It is worthy of 

 remark that the first of these lines is faint and the last is the brightest 

 of the group. The group wave-length 5355, 5336, 5319 have been 

 all reversed, but the last of the three (5319) was the most difficult 

 to reverse : it is also the feeblest of the group. In the more refran- 

 gible group, wave-length 5112, 5095, 5081, the least refrangible is 

 the only one reversed. 



Making a general summation of our results respecting the alkaline 

 earth metals, potassium, and sodium, and having regard only to 

 the most characteristic rays, which for barium we reckon as 21, for 

 strontium 34, for calcium 37, for potassium 31, and for sodium 12, 

 the reversals in our experiments number respectively 6, 10, 11, 13, 

 and 4. That is in the case of the alkaline earth metals about one-third, 

 and these chiefly in the more refrangible third of the visible spectrum, 

 the characteristic rays remaining unreversed in the more refrangible 

 part of the spectrum being respectively 2, 5, and 4. In the case of 

 potassium we reversed two in the upper third, all the rest in the least 

 refrangible third. These experiments relate to mixtures of salts of 

 these metals combined with the action of reducing agents. In a 

 future communication we will contrast these results with those of the 

 isolated metals, calcium, strontium, and barium. 



IV. " Note on the unknown Chromospheric Substance of Young." 

 By G. D. Ltveing, M.A., Professor of Chemistry, and J. 

 DiTWAR, M.A., F.R.S., Jacksonian Professor, University of 

 Cambridge. Received March 27, 1879. 



In the preliminary catalogue of the bright lines in the spectrum of 

 the chromosphere published by Young in 1861, he calls special attention 

 to the lines numbered 1 and 82 in the catalogue, remarking that 

 "they are very persistently present, though faint, and can be dis- 

 tinctly seen in the spectroscope to belong to the chromosphere, as such, 

 not being due, like most of the other lines, to the exceptional elevation 



