Pottox—Spectrographic Analysis of Commercial Thallium. 341 
to which the micrometer was adjusted being marked by an 
asterisk. 
Column two, headed ‘“‘ Mark and Intensity,” gives the marks 
over or under the lines if any, dots, dashes, and triangles, being 
the most convenient marks to use, and the intensity of the lines 
indicated by the letters S., M., and f., for strong, medium, and 
faint, corresponding roughly with intensities 10, 6, and 2; very 
strong lines may be marked 8.8., and very faint ones, no more 
than visible, ff. 
Column three, headed ‘‘ Curve Reading,” gives the readings 
on the curve corresponding to the actual measurements on the 
micrometer for the fiducial gold lines, and the amounts to be added 
to or subtracted from the various micromatic measurements to 
adjust them to the curve. 
Column four, headed ‘‘ Wave-Length, Rowland Scale,”’ gives 
the wave-length given by the curve corresponding to the corrected 
measurement. 
Column five, headed “ Element and Accepted Wave-Length,” 
gives the symbol of the element to which the line is due, its 
accepted wave-length, intensity and persistency, and any other 
notes that may be necessary. 
From the list of identifications, it is obvious that the impurities 
are lead, tin, copper, and aluminium; and it will be noted that 
the lines showing correspond with the residuary lines of these 
elements as determined by Professor Hartley.1 The relative 
persistency of the lines is represented by the letters 9, x, ¥, 
and w respectively, and the intensities, ordinarily accepted, are 
shown enclosed in brackets. 
One or two lines were not identified with certainty, and 
are left blank. 
1 Phil. Trans., 1884; Part I., pp. 49-62; Part II., pp., 325-342. 
[MeaASUREMENTS OF SPECTRA. 
