260 
MAJOR A. E. OXLEY ON THE INFLUENCE OF I^IOLECULAR 
As hi for diamagnetic media is of the order — 7 x 10“’', the second term in (2) is 
insignificant in comparison with ^ ■ hi. 
If c be the compressibility of the liquid, the change of volume in cubic centimetres 
per cubic centimetre will be given by 
h:=^.C.hi.W .(3) 
This relation has been experimentally verified by Quincke."^ The compressibility c is 
of the order 10“^“, particular values for different substances being :—■ 
Substance. c x 10^'’. 
Benzene. 0'8 
Chlorobenzene. 0’7 
Toluene. 0'8 
Xylene. 07 
Water. 0’5 
Carbon tetrachloride .... 0‘9 
Acetic acid. O'4 
Carbon bisulphide.O'9 
Substance. cxl0^~. 
Mercury. 3'7 
Potassium.31'5 
Sodium.15'4 
Lead. 2'2 
Tin. 1-7 
Bismuth. 2'8 
Iron. 0'4 
Since the largest magnetic field at our disposal is 50,000 gauss, the largest value of 
Jv is 
-4x 10-i''x7x 10-^x2'5x 10-' =-8x 10“® =-10“^ 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 
1. hi . + i . a',. P 
per unit volume, where a'^ is the constant of the local molecular field and I is the 
aggregate of the local intensity of magnetization per unit volume. The term 
■g-. a'g. V is associated with each cubic centimetre of the crystalline structure whether 
* See G. T. Walker, “ Aberration and the Electromagnetic Field,” ‘ Camb. Univ. Press,’ pp. 72-83. 
