What is the cause of bodies being either solid, liquid, or aeriform?

When the principle of attraction prevails, it causes them to become solid; when caloric prevails, they become aeriform.  Fluidity is, apparently, a medium between the two.

How is the state of Solidity in bodies accounted for?

The particles of all bodies are subject to two opposite powers, repulsion and attraction; between which they remain in equilibrium.  While the attractive force remains strongest, the body remains in a state of solidity; but if heat destroys this force, the particles lose their cohesion, and the body ceases to be solid.

     Cohesion, act of sticking together, union of the
     constituent parts of a body.

Which is supposed to be the most natural state of all bodies?

Solidity; for by the combination of caloric with them we can reduce most substances to the fluid state; while the greatest number of liquid substances take a solid form by the loss of caloric.  Thus, water congeals and forms ice; and even the gases show this disposition to become solid, when they lose their elasticity by forming some combination.

Explain the terms Repulsion and Attraction.

Repulsion is a peculiar property in the particles of matter, which gives them a constant tendency to recede from each other.  Attraction is an unknown force, which causes bodies or their particles to approach each other.  The particles of all bodies possess this property, which causes them to adhere, and preserves the various substances around us from falling in pieces.

What different kinds of Attraction can you mention?

Attraction may be distinguished into that which takes place between bodies at sensible distances, and that which manifests itself between the particles of matter at insensible distances.

Give an example of the first kind of attraction.

One of the most familiar instances of attraction at sensible distances is seen in the descent of heavy bodies to the ground.  When a stone is lifted up in the hand, the earth’s attraction, which previously caused it to remain at its surface, is overcome; but, as soon as the hand is withdrawn, the stone falls to the earth.  The force which causes this is called the attraction of gravitation, or simply gravitation.

How is the second kind of attraction, or that between the particles of bodies, subdivided?

Into the attraction of aggregation, or cohesion; and chemical attraction, or affinity.  The former takes place between particles which are similar, and the latter between those which are dissimilar.  All the operations of chemistry are founded upon the force of affinity which Nature has established between the particles of different kinds of matter, and which enables the chemist to produce new compounds differing more or less from the substances by whose union they were formed.