Page:Various Forces of Matter.djvu/67

 after leaf, and see how that enables the light to pass through to the screen, and how, as Dr. Tyndall turns it round in his hand, you have those different colours, pink, and purple, and green, coming and going most beautifully;—not that the mica is more transparent than the glass, but because of the different manner in which its particles are arranged by the force of cohesion.

Now we will see how calcareous spar acts upon this light,—that stone which split up into rhombs, and of which you are each of you going to take a little piece home. [The mica was removed, and a piece of calc-spar introduced at .] See how that turns the light round and

round, and produces these rings and that black cross (fig. 20). Look at those colours, are they