COLOUR STUDIES WITH THE MICROSCOPE. 
131 
it is crude. No turning the polariser or analyser gets rid of 
this crudity, though some improvements may be made. Now 
introduce selenite on the stage : say Mr. Ackland’s construction, 
using the bottom plate only, so as to get, with the right positions 
of polariser and analyser, a pale yellowish green tint. Two 
beams of the cross in the slide before the writer now appear 
pink, shaded; two others pale blue, and four others green, 
shaded and varied in tint. This is a great improvement upon 
the former trials, but the pattern is not a good one, and the 
colours look too separate to blend. A little pleasant variety is 
obtained by placing Ackland’s -§- selenite over the foundation 
one of his apparatus. With this combination some flowery 
patterns adjacent to the big circles and crosses come out with 
more variety and harmony. We find now contrasts of green 
or yellow, and red purple, no colour standing too sharply 
or in too large masses. A salicine slide prepared with colloid 
silica, and crystallized in elegant little rosettes, being placed in 
the field shows blue, yellow, orange and red, all looking crude. 
Eevolving the analyser works no satisfactory improvement, but 
several positions of the polariser introduce harmony, and in 
some we notice elegant citron greens relieved by purples, pale 
tints, light yellow, and reddish brown, well disposed. This by 
another position of the polariser is all made ugly, through the 
introduction of inharmonious orange red. Beauty is again 
obtained by a slight left rotation of the bottom selenite on the 
stage, and we have sage and other greens with purples, violet, 
and something like primrose, well, arranged. 
Another richly foliated salicine slide affords amongst other 
tints fine bluish greys, well harmonized by their surroundings. 
Cupric sulphate with silica, or by other means made to give 
spiral forms, rosettes, and patterns something like loosely 
twisted hanks of wool, affords very fine effects, abounding in 
tertiary tints. Cupric and magnesic sulphate crystallized 
together in somewhat similar patterns are also very useful. One 
before the writer gives, in one position of the polarising appa- 
ratus, an ugly contrast of blue, orange and golden brown badly 
assorted, but which can be instantly changed to sage green and 
other tints of great beauty by slight motion of the polariser to 
the left. 
With the selenites arranged to give a pale neutral tint ground 
not differing much from white, a slide of hippuric acid in floral 
rosettes, affords bluish greys, dark and light ; pale greeny greys, 
and fawns, all subdued tints, exquisitely combined. 
Cadmic chloride in detached patterns, like small nosegays of 
various flowers and leaves, presents an admirable pattern when 
the apparatus gives a neutral tint ground. By varying the 
selenites and their position, several fine changes are obtainable. 
