34 Prof. Everett on Normal Piling as 
spherical shells, the enclosed nucleus of grains being in 
normal piling. The surface of misfit, together with the 
enclosed nucleus, is called a negative inequality ; and the 
magnitude of the negative inequality is reckoned by the 
number of grains which are deficient. 
According to the theory, these surfaces of misfit travel 
through the grains after the manner of solitary waves. The 
mode of propagation is, that the impulses propagated through 
external grains towards the loose joint are stronger from one 
side than from the other, and there is a preponderating 
transfer of grains across the gap in obedience to the stronger 
impulse, causing the gap to travel in the opposite direction, 
as a geometrical consequence ; just as a bubble travels up- 
wards through water in virtue of the water moving down- 
wards. ; 
Each of these negative inequalities is an atom of ordinary 
matter: what we call the momentum of moving matter being 
merely the manifestation of the real momentum of grains 
moving in the opposite direction. The apparent mass of an 
atom is measured by the number of grains that are wanting 
in its surface of misfit. Calculations are given to show that 
a moving surface of misfit tends to continue moving with 
a uniform velocity of translation and with unchanged 
magnitude. 
Again, calculations are given to show that two of these 
surfaces of misfit have a tendency to approach each other. 
The argument is to the effect that their mutual approach 
increases the average compactness of arrangement, and is 
therefore promoted by the perpetual battering from outside 
which is equivalent to hydrostatic pressure. Furthermore, 
the calculation shows that the mutual force between the two 
atoms varies inversely as the square of their distance. 
Gravitation is thus explained as a partial relief of pressure in 
front, allowing a vis a tergo to prevail. 
This calculation of attraction inversely as square of distance 
is based on a first approximation, which is sufficient when 
the distance is a large multiple of the diameter of an atom. 
It neglects the square of the small ratio of the diameter to 
the distance. But when the two atoms are very close, this 
square must be taken into account. At a certain small 
distance it gives much stronger attraction, thus explaining 
cohesion and surface-tension ; and for still closer approach 
it gives repulsion. 
Again, electricity is explained by a particular kind of 
disarrangement called a complex inequality. It is conceivable 
