90 
PROFESSOR W. N. HARTLEY AND MR. W. E. ADENEY 
It was originally intended that these spectra should be drawn on the same scale as 
Cornu’s map of the solar spectrum; this would have necessitated scales and drawings 
eight feet in length for each of the sixteen spectra. The work was actually com¬ 
menced, but the mapping of every line proved too laborious; accordingly enlarged 
photographs of the prism spectra, about thirty-six inches in length, have been utilized 
by writing the wave-length over each line. These photographs are intended to serve 
for particular reference. In addition, each line has been carefully described, and its 
position on the photographed spectra has been very carefully determined and recorded 
in the scale numbers. For the purposes of chemical analysis, small maps and actual 
photographs, showing the characters of the lines, are of most value, and accordingly 
the principal lines have been drawn on the scale of wave-lengths on sheets of a size 
convenient for reference and comparison with a series of prism photographs ten inches 
in length. The scale numbers refer to spectra of about one-half these dimensions. 
Should it be found necessary at any time to rectify any of the wave-lengths given in 
this paper, this may be easily accomplished by the use of an interpolation curve, 
derived from the scale numbers and true wave-lengths. 
In all cases where the wave-lengths on the maps differ from the numbers in the 
tables the latter must be considered as the more correct, the drawings being on too 
small a. scale to admit of great accuracy, and moreover some of the numbers were 
slightly altered after the maps had been drawn. 
Descriptions of Spectra and Tables of Wave-Lengths. 
Full particulars concerning the method of producing the prism spectra, together 
with an account of the electrodes employed, have been already published in the 
Scientific Transactions of the Royal Dublin Society, and the characters of the various 
lines observed is there defined. 
A peculiar feature of certain lines in the spectra of cadmium and indium has been 
observed, we believe, for the first time by us. The lines are continuous lines, but 
they do not extend from the point of one electrode to the other, but occupy only an 
intermediate position, commencing and terminating at some distance from the metallic 
points. A similar character is observable in certain air lines, when strong metallic 
lines occur in close proximity on either side. In both air lines and metallic lines the 
central portions become stronger, and the ends fade away as the temperature is 
increased. Lines which show this in a marked degree are those of indium with 
wave-lengths 24295, 2389"8, 2332"2, and that of cadmium with wave-length 25445. 
In a less remarkable manner the following lines represent this character in cadmium : 
3080-2, 2868-0, 2832-3, 2774*5, 2763-1, 26585, 2635*3 ; in indium, 2956*1, 27093, 
26025, and 2520"9. Air lines altered by the proximity of metallic lines are the 
following : 3408-0, 33295, 30075, and 27335. 
