A Theory of the 
[November, 
646 
dyad therefore melts at a higher temperature than a monad, 
and a triad at a higher temperature than a dyad. The same 
increment of heat causes less expansion where each atom 
has a number of poles than when the poles are few : the 
vibratory movements constituting heat and electricity can be 
more readily communicated from atom to atom when they 
are near together, but unconstrained by manifold attractions 
to move within narrow limits. 
Chemical force is, in a sense, a polar and dual force. 
Positive poles attract negative poles, but they do not repel 
positive poles ; on the contrary, they exert an attractive 
influence of indefinite character upon all positive poles within 
the range of their power. Chemical poles aCt inductively, 
not only upon each other when in the same atom, but upon 
poles in other atoms. If the intensities of the poles are 
unequal, but of like kind, the stronger pole induces in the 
weaker pole an intensity equal to its own, but of opposite 
kind, and the difference between the induced intensity and 
the original intensity of the weaker pole is the measure of 
the affinity between the two poles. Since no two elements 
have exactly the same affinity it is always possible for them 
to combine (under proper conditions of temperature, &c.), 
but the more nearly equal and alike are their affinities the 
less is the attraction between them. 
There is under certain circumstances definite union be- 
tween atoms of the same element. This arises when the 
general diffusive attraction of poles, or cohesion, is overcome 
by heat. In the solid, cohesion of atoms produces rigidity, 
hardness, elasticity, and the ordinary phenomena of solidity. 
In the solid, each pole is bound by attraction to a number 
of other poles, and its motion is confined within a narrow 
range. As the temperature increases its tendency is to 
overcome the cohesion of the poles, but one pole has always, 
by force of position, a greater cohesion for one other pole 
than for the rest. As the atoms break away from one another 
the hardness, rigidity, and elasticity of the solid decrease. 
At a certain stage each atom on an average coheres to two 
others, to one more strongly than to the other. The solid 
has then reached the pasty condition immediately preceding 
liquefaction. As the temperature increases the third atoms 
begin to break away, being themselves held more powerfully 
by other atoms ; the solid is now melting. Finally, when 
all the cohering atoms have formed into pairs, each atom of 
which is free to roll round the other, complete liquidity is 
attained. The atoms, however, are still sufficiently near 
together for each pole, as its atom rotates round its fellow, 
