18790 
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PROCEEDINGS OF SOCIETIES. 
Royal Society, June 19. — “ Note on ‘ Spectroscopic Papers,’” 
by G. D. Liveing, M.A., Professor of Chemistry, and J. Dewar, 
M.A., F.R.S., Jacksonian Professor, University of Cambridge. 
In a recent communication to the Royal Society, Mr. Lockyer 
has criticised the author’s statement of Young’s wave-lengths 
identifications of certain chromospheric lines. As to the wave - 
lengths, the authors throughout their table omitted all figures 
after the decimal point merely for the sake of not cumbering the 
table. The numbers, Young mentions, are not his own, but 
taken from Angstrom’s catologue. Moreover, as to Young’s 
identifications with metallic lines, he states expressly that they 
were taken from the maps of Kirchhoff, Angstrom, and Thalen, 
and Watts’s “ Index of Spedtra.” Their objedt 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. They mentioned, in relation to 
aluminium, the two lines with wave-lengths 6245*4 an d 6237*3 
seen by Young, not because they 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 there is the remark- 
able fadt 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 potassium lines which are often seen as one, not 
merely from want of dispersive power (which with prisms is 
usually sufficient at the violet end), but because the lines are 
expanded until they meet. The authors at first saw them re- 
versed as one broad line which divided in two as the potassium 
evaporated. The authors never set themselves to determine 
exadt wave-lengths ; but they sought to determine the conditions 
of reversal, and they used wave-lengths for the convenience of 
indicating the lines of which they wrote. In general they 
determined the identity of a dark line with the corresponding 
bright line by observing that both had the same place on the 
cross-wires, or pointer, or both gave the same reading of the 
scale of the spedtroscope. They then gave the wave-length of 
the bright line as determined by some good authority, usually 
either Thalen or Boisbaudran. When they could not identify 
the dark lines in that way, they took the readings of known 
lines with their spedtroscope, using, for lack of sunshine, most 
