PVROELECTRICITY AND PIEZOELECTRICITY 163 

 and 



0\dOJx 0- 



Then fd0\ x dK _#_ 



dO po-f 



If we integrate from x = to x = x the total change in 6 is 

 small, so that we may put constant on the right hand and the 

 change is 



* . dK . 

 ~ dO o- 



= _ _ 



HTT K dO pa- 



where E is the intensity. 



This is much smaller than the value just found for a pyro- 

 electric crystal, unless E is very much greater than 100. 



It is easily found that the isentropic capacity 



dm\ A.^ 



= cl + 



and ,- is found to be 

 be 



which 'is quite negligibly small.* 



* Pockels has generalised the theory of Lippraann. The reader is referred to 

 Winkelmann's Ifandbuch, vol. iv. , where a full account of pyro- and piezoelectricity 

 will be found, with references to the original memoirs. 



KE 2 ,M dK\*_0_ 

 47r \ K dO/ pa- 



