36 
THE ASTRONOMER ROYAL, WAVE-LENGTHS 
duces a line corresponding in spectral position to the line here measured. This Table 
is, in fact, Kirchhoff’s Table, with the insertion throughout of one column containing 
the computed values of the wave-lengths. In copying the first column, I have endea- 
voured to copy the’ braces and brackets of Kirchhoff’s Table, -without in every case 
understanding their application. 
The Table which next follows is Kirchhoff’s special Table for the lines produced by 
the metals Cerium, Didymium, Lanthanum, Palladium, Platinum, Puthenium, Iridium, 
with the corresponding wave-lengths. Two of its compartments contain the lines in a 
combination of Lanthanum and Didymium, and in a combination of Ruthenium and 
Iridium. It is accompanied by a similar Table of lines produced by the atmosphere. 
The next Table (formed by myself) contains the wave-lengths for each of the metals 
whose lines have been measured by Kirchhoff, and are contained either in the General 
Table of lines of the solar spectrum, or in the smaller special Table which I have just 
described. The numbers are simply extracted from those Tables. I may mention that 
my original intention was to confine my computations to these metal-lines, in the hope 
that they might give some assistance to the formation of a mechanical theory. 
The two last Tables contain the comparison of direct measures of the wave-length 
made by Angstrom and Ditscheiner with the computed measures given in the General 
Table, as far as the identity of the lines appears to be established. Angstrom’s measures 
were given in terms of the Paris inch : I have preserved these ; and have also given 
their equivalents in terms of the millimetre. 
I have only to add that, in my original communication to the Royal Society, dated 
1867, March 2, the modifications of the first computed numbers, now introduced after 
consideration of Ditscheiner’s later measures, had not been applied. I have now 
incorporated them in the finished Tables, with the permission of the President and 
Council of the Society. 
G. B. Airy. 
Boyal Observatory , Greenwich , 
1867, October 35. 
