260 MAJOR A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 



As ki for diamagnetic media is of the order 7xlO~ 7 , the second term in (2) is 

 insignificant in comparison with \ . k t . H 2 . 



If c be the compressibility of the liquid, the change of volume in cubic centimetres 

 per cubic centimetre will be given by 



(3) 



This relation has been experimentally verified by QUINCKE.* The compressibility c is 

 of the order 10~ 10 , particular values for different substances being : 



Substance. c x 10 10 . 



Benzene ........ 0'8 



Chlorobenzene ...... 07 



Toluene ........ 0'8 



Xylene ........ 0'7 



Water ........ . 0'5 



Carbon tetrachloride . . . . 0'9 



Acetic acid ....... 0'4 



Carbon bisulphide ..... 0'9 



Substance. c x 10 13 . 



Mercury ........ 37 



Potassium ........ 31 '5 



Sodium ........ 15'4 



Lead ......... 2'2 



Tin .......... 17 



Bismuth ........ 2 '8 



Iron ......... 0'4 



Since the largest magnetic field at our disposal is 50,000 gauss, the largest value of 



Sv is 



-|xlO- 10 x7xlO- 7 x2-5xl0 9 =-8xlO- 8 =-10- 7 c.c./c.c. 



Now we have shown (Part III., p. 90) that the potential energy term corresponding 

 to (2) for a crystalline medium is 



2 -1 



-- 



1 n' T 2 



2- a c- i 



per unit volume, where a' c is the constant of the local molecular field and I is the 

 aggregate of the local intensity of magnetization per unit volume. The term 

 3- . a! c . I 2 is associated with each cubic centimetre of the crystalline structure whether 



* See G. T. WALKEK, " Aberration and the Electromagnetic Field," ' Camb. Univ. Press,' pp. 72-83. 



