Adkney — Photographs of Spark Spectra from the Rotvland Spectrometer. 337 



si^ectra are in preparation, but it has been thought inadvisable to delay the pub- 

 lication of reproductions of the spectra until the measurements are completed, 

 both on account of the differences in number and character of the lines above 

 referred to, and also on account of the very clear way in which the characters of 

 the s^jectra and of their component lines are shown therein. 



Scales of wave-lengths, based upon Kayser and Runge's measurements of the 

 iron lines, have been ruled on the original photographs, by means of which the 

 lines in the spectra may easily be identified, or otherwise, with measurements 

 which have already been published in various tables of wave-lengths. 



Each scale division is equal to five units on Rowland's scale ; the division of all 

 the scales are very nearly of equal magnitude in linear measurement. They have 

 been ruled in two portions corresj)onding to the two sections in which the spectra 

 had been photographed. The division on the less refrangible sections are each 

 approximatel)^ equal to -0944 inch, and those on the more refrangible sections to 

 •0943 inch. 



A vernier has been ruled for each section, by means of which the wave-lengths 

 of the lines may be approximately read off to 0"25 of a unit. 



The errors of the scales of each spectrum are approximately given in the 

 following table : — 



Less Kefeangible Section. 



More Refrangible Section. 



Pd, Cr (Pt & K), Au, . 

 Ye, Eh, Pt, Mn (Pt & K), 



03 



Co, . 

 Ir, . 

 Ni&Ru, . 



