ACTION OF CALOSPAR ON LIGHT. 



55 



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 

 A.] See how that turns the light round and 



Fin. 20. 



round, and produces these rings and that black 

 cross (jig. 20). Look at those colours, are they 



E 4 



