and Pyroelectric Properties of Matter. 9 



If we suppose t f — t to be infinitely small, these expressions be- 

 come respectively, in accordance with the previous notation : — 



(i.) J Jv-o, 



where e denotes the value of e for (x Q , y Q , z , f > Vi ?o> 5 

 (II.) K+^tf-t); 



(IV.) -H. 



Hence we have 



* * ~ i(* + + ? 



J<fel* t} -H 



+ i(*+0 + * ; 



or, since e — £ is what we have denoted by e, 





and the expression of the Second Thermodynamic Law becomes 



AL^_ 1 i 6 -o ^ 



Eliminating e from this by (4), we have 



t du 

 J ~dt 



H=-^; (6) 



and, eliminating H, 



dw , . 



e=w -<* < 7 > 



This is equivalent to 



e=eo + w—t-^i (8) 



or, if N denote the specific heat of the mass at any tempera- 

 ture t, when kept constantly in the mechanical state {x Qy y , z , 

 %o, Vo, So) ? 



€■ 



C* dw 



:JJ N ^ + ^-^, .... (9) 



