400 Joty—NSome Sedimentation Experiments and Theories, 
most general condition will be that particles separated by molecular distances will 
experience preponderating clumping forces tending to retain them in juxtaposi- 
tion, and to further retain in the group any particles urged into contact with it. 
The particles are, in fact, everywhere expelled from the electrostatic field on the 
energy principles referred to; the phenomena being the inverse of those which 
occur when a plate of sulphur is drawn further inwards (replacing air) between 
the electrified plates of a condenser. Although we must look to the mechanical 
forces arising from lines of force which are not symmetrically distributed across 
silt particles tending to straighten and expel laterally the particles of low specific 
inductive capacity, we may state the matter more generally in the view that 
_ the silt exerts an influence opposed to the ionising forces existing in the liquid 
medium, and these forces consequently reacting on the silt, tend to reduce the 
de-ionising influence of the silt by favouring its expulsion from the medium. 
In a medium exerting this expulsive force upon the suspension any mutual 
attractions arising in the electric sign of the particles will go towards explaining 
how silt particles possessing a charge might flocculate or clump more rapidly than 
those deprived, or almost deprived of this charge. Such attractions might arise 
in reversal of sign of some small particles by attraction to the negatively charged 
particle of positive ions ; or local reversal of sign in the case of large particles; so 
that particles become mutually attractive. Again, the preponderating attractive- 
ness for + ions of the larger particles in a region where silt particles were adjust- 
ing their positions under the electric forces may lead to approximation of the 
smaller silt particles to the larger. 
But obviously in a medium possessing these expulsive properties it is only 
necessary to confer active motions upon the repelled particles to ensure their 
rapid aggregation. For in such a medium final stability is only attained by 
ageregation. ‘The mutual approximation of the particles is a position of stability, 
their separation is not. Hence each encounter reduces the number of separate 
free particles. Now it is certain that in the existence of an electric charge upon 
the silt there arises a cause of motions among the particles which a neutral silt 
would not possess. Whether repulsions between negative silt and negative ions, 
or attractions between silt to positive ions, the results are activity. Nor need the 
mutual repulsion of the particles oppose final clumping, for it will everywhere 
happen that particles urged into collision are neutralized wholly or partially 
before this repulsion can effect separation. 
We are in complete ignorance of the actual mechanism of the ionising forces 
in a liquid such as water; but that its high specific inductive capacity is probably 
concerned in its remarkable ionising power by weakening the electric forces 
between the ions has been pointed out by Professor J. J. Thomson. And it is 
very certain that the effect of the silt is to tend to undo this work of ionisation. 
On these premises the foregoing remarks are based. 
