395 



relations between melting point, expansion etc. But no definite 

 statement of the periodicity of coefficient of linear expansion of 

 elements witli their atomic weiglits is available. 



Grüneisen [Ann. Phys. J 910 (IV), 33, 33—64] has found that the 

 observed expansion of metals by heat is, in general, in close agree- 

 ment with that required by Thieskn's (Ber. Deut. Phys. Ges. 1908, 

 6, 947) exponential formula 4— /,=.// (7','+'^— Tji+e) and this agree- 

 ment is particularly good at low temperatures. The experimental 

 given e is a periodic function of the atomic weight of the metal and 

 that its maximum values are reached when the atomic volumes are 

 at their respective minima. It has now been found out that the 

 coetBcient of linear expansion of elements is also a periodic property. 



-^ Atomic weights of elements 



Fig. 5. 



By plotting the values given in L.vnuolt und Börnstein's Tabellen 

 well defined periodic curves are obtained. The alkali metals lie on 

 the topmost points, whilst S, Se and Te lie on a straight line on 

 the ascending portions of the curve. 



Cu, Ag and Gold, as v\ell as As, Sb and Bi occur in similar 

 positions in the minima. 



Molecular Magnetic Rotation. 



If we imagine a layer of unit lengt li of any substance placed in 

 a magnetic field of unit intensity and traversed by a beam of homo- 



