166 



Profs. Liveing and Dewar. 



[June 19, 



The employment of various fluids for immersion lenses is carefully 

 considered ; and the singular property of castor oil discovered by the 

 writer is referred to. 



As the Society honoured the writer by inserting in their " Trans- 

 actions " a paper on "A Searcher for Aplanatic Images," he now 

 introduces a new form which offers some advantages : by its extended 

 traverse, by its simplicity and economy of light with increase of magni- 

 fying power. 



Finally, some examples are given of producing transcendent defini- 

 tion in cases found hopeless by a numerous body of observers ; as the 

 papers written in " The Monthly Microscopical Journal " during the 

 last ten years abundantly demonstrate. The means also of its attain- 

 ment are minutely described. 



VII. "Note on 'Spectroscopic Papers.'" By G. D. LlVElNG, 

 M.A., Professor of Chemistry, and J. Dewar, M.A., F.R.S., 

 Jacksonian Professor, University of Cambridge. Received 

 May 29, 1879. 



In a recent communication to the Royal Society, Mr. Lockyer 

 has criticised our statement of Young's wave-length identifications 

 of certain chromospheric lines. As to the wave-length, we have 

 throughout our table omitted all figures after the decimal point 

 merely for the sake of not cumbering the table. The numbers, 

 Young tells us, are not his own, but taken from Angstrom's cata- 

 logue. Moreover, as to Young's identifications with metallic lines, 

 hie states expressly that they were taken from the maps of Kirchhoff, 

 Angstrom, and Thalen, and Watts's "Index of Spectra." But our 

 object was not to criticise Young's work, but only to use it for the 

 purpose of comparing the behaviour of certain metals on the earth 

 and in the sun, and the conditions under which certain lines appear, 

 or do not appear, or are reversed. 



We should perhaps have made our meaning clearer if we had given 

 another column with the wave-lengths of the metallic lines referred to 

 side by side with Young's numbers for the chromospheric lines. We 

 mentioned, in relation to aluminium, the two lines with wave-lengths 

 6245*4 and 6237*3 seen by Young, not because we thought their 

 identity with the aluminium lines proved, but because they are the 

 only two lines in Young's table which are at all close to aluminium 

 lines, and if they be not due to that metal, then we have the remark- 

 able fact that aluminium in the sun gives no lines either dark or bright 

 except the two which have been reversed on the earth. A somewhat 

 similar remark applies to the potassium lines, only in that case 

 Young's line has a wave-length very nearly the mean of the two 



