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POPULAR SCIENCE REVIEW. 
A nearly black ground, a gros bleu one, and a pale blue, being 
among the best. 
By comparing the effects produced when substances are crys- 
tallized so as to afford considerable masses of the same tints, 
with others in which no single tint occupies a large part of the 
field, but a considerable variety of tints affect the eye at once 
whichever part is looked at, will show how much a due propor- 
tionment of quantities has to do with artistic results. It will 
also be noticed that when a good effect is obtained, it will not 
always bear transposition to the corresponding complementary 
tints without the beauty being lost, and not unfrequently ugli- 
ness replacing it. This is analogous to music, which is very 
often spoilt by transposition to another key. 
It is probable that most of the experiments described could be 
shown in a lecture-room by the new American lanterns and suf- 
ficiently large polarising apparatus, but private study with the 
microscope could not be dispensed with. 
Among minerals which may give good colour lessons and 
suggest patterns, may be mentioned serpentine, agates, lapis 
lazuli, manganese crystals in talc, opalized woods, sulphur 
crystallized from its solution in bisulphate of carbon, &c. &c. 
