Piezo-electric Property of Quartz. 335 



direction of the strain, are shifted to parallel positions with 

 distances between the atoms in them unchanged. Hence the 

 atoms in these rows contribute nothing to the electrical effect. 



Fig. 2. 



©-Q B-Q. 



\ 



©)-e N ^-e^ B-e^ 



9-¥-©-e4(-©-e-)(-© 



V -/\ j \ l\ j \ l\ i 



v ©-© 7 ©>-© y v ©-© 7 



©-© 



/ 



©-©■ 



©-© x 



N ©-© 



But, in parallels to these rows, on each side of the centre of 

 each molecule, we find two pairs of atoms whose distances are 

 diminished. 



