424 , Mr. W. Sutherland on the 
like a number of spinning tops in the field of gravity. 
During the vibrations it will sometimes happen that the 7 
and the » of two adjacent doublets come so near one another 
that their attractions break up the doublets to form a new 
one, and liberate h and % at about two molecular diameters 
apart. These in rushing together may be regarded as free, 
and may upset the stability of other doublets. Thus we 
must allow to each electron the average free time and free 
path postulated by Riecke. ‘This dissociation is characteristic 
of the doublets in metals and causes metallic conduction. 
The reason for the profound distinction between metals and 
insulators is that in the monatomic molecule of the metal 
both J and ) are in the same atom, whereas in compounds 
fandb are generally in different atoms. lor instance, in 
NaCl we have % attached to Na and b to Cl, as proved in the 
electrolysis of fused NaCl. Thus the fin Na, if it approaches 
the ) of the Cl in another molecule, will not break away, 
because of the decided affinity of the % for Na and of the 
b for Cl. Unless the molecule of NaCl breaks up and allows 
electrolytic conduction to take place, NaCl acts as an insu- 
lator. The monatomic atom of a metal with its doublet is 
what I have proposed to call a stion. Metallic conduction 
is due then to the dissociation of stions, electrolytic conduc- 
tion to the dissociation of molecules. In the case of the 
Helium family the stions may not dissociate, in which case 
these elements in the solid state would not conduct like 
metals. The electrons in the atoms of these elements may 
be inside instead of on the surface, as appears to be the case 
with the metals. In insulators, then, each atom confines its 
own electron or electrons to its own immediate neighbourhood 
and allows no free time. 
In metallic conduction, then, we have to do with the 
breaking of molecular electrical gyrostats and the flying 
together of the broken pieces. or simplicity, we can re- 
place the actual discontinuous process of nature by an imagi- 
nary equivalent in which each gyrostat preserves a continuous 
existence, while also a certain number of free electrons travel 
between the gyrostats, propagating momentum to the same 
amount as the shocks occurring in the natural process. In 
a metal of varying temperature the transmission of energy is 
-greater from hot to cold than in any other direction because 
the free electron carries with it the kinetic energy of the 
temperature ruling where it gained its freedom, and so we 
-have the conduction of heat. In metals, of course, there will 
_be also the usual molecular conduction of heat as in insulators. 
-On the present occasion we shall treat the conduction of heat 

