IN PRACTICAL ASTRONOMY, SPECTROSCOPICALLY EXAMINED. 843 
herein-before opened-up. The other, the bluish Oxalate of Chromium and Potass, is also di-chroic, but 
has this further feature of interest, that it shows a fixed black line, as well as locomotive bright colour 
bands. (See also p. 782.) 
PLATE III., No. 43 oF ta1s Vou. XXVIII. 
This Plate, of 25 very distinct and recoverable colours, with seven variations in degree of each, 
with which Messrs W. & A. K. Johnston, the Society’s able engravers, have kindly taken a deal of 
trouble and much anxious interest, will, with their splendid chromatic printing, probably explain itself 
on inspection better than any mere words in this place can attempt to do: the principles on pp. 789 to 
791 having been previously studied. P. Ss. 
