ELECTRIC ABSORPTION OF CRYSTALS 211 



in quartz and selenite also confirms the theory, provided that we can 

 show that in the given piece of quartz some molecules of right-handed 

 quartz were mixed with the left; for we know that the theoretical con- 

 ditions for the absence of electric absorption are rarely satisfied by 

 laminated substances like selenite or mica. If the theory is con- 

 firmed, the apparatus here described should give the only test we yet 

 have of the perfect homogeneity of insulating bodies; for any optical 

 test cannot penetrate, as this does, to the very structure of the 

 molecule. 



