The Void--Why are we not Aware of Certain Bodies?by Rene Descartes
Why can’t we sense the aether?
If we could sense it, we will free ourselves from an error with which we have had since childhood, when we believed that there were no other bodies around us except those that could be sensed.
Thus that, if the aether were one of them, then, we would sense it so very faintly that it could not be as material nor as solid as those other bodies [matter] that we sense more clearly.
The Aether Fills All
All bodies, both hard and liquid, are made from the same aether.
It is impossible to conceive of the parts of that aether that are more solid or occupying less space than when they are compacted . It follows that liquid bodies have void*, if there can be a void anywhere, but hard bodies do not. Because of this void, the parts of the liquid can much more easily press and arrange themselves against one another than those of hard bodies.
*Superphysics note: Here, the aether-void is one of the properties of the aether
For example, if you place powder in a jar, you can shake the jar and pound against it to make room for more powder. But, if you pour liquid into it, the liquid spontaneously arranges itself in as small a place as one can put it.
Philosophers do experiments to show that there is no void in nature.
In all spaces that people think are empty and only have air, there is actually the same aether that we use to sense other bodies.
Why would nature cause the heaviest aethereal bodies to rise and the most solid aethereal bodies to break?
Nature does this in certain machines which have parts that do not touch one another yet keep the machine in operation.
Water in a well does not go up to fill the pipe of a pump without a void in that pipe. Likewise, the water in clouds do not fall to fill the ground if that ground were not void of water. 
Liquids only move because there is some empty space among them, at least in the places where they left as a consequence of their motion.
This is explained by the circular motion of all the motions in the universe. When a body leaves its place, it always enters into that of another. The latter into that of still another, and so on down to the last which occupies in the same instant the place left open by the first.
Thus, there is no void among them both when they are moving and not moving. Circular motion does not mean a motion in a perfect circle.
When bodies move in the air, we do not usually notice these circular motions because we are used to conceiving of the air only as an empty space. But look at fish swimming in a pool. if they do not approach too near to the surface of the water, they cause great speed.
It shows that the water that they push before them does not push on all the water of the pool, but only the water which can perfect the circle of the fishes’ motion and return to the place they leave behind.
All motions are circular. When the wine in a cask does not flow through an opening at the bottom because the top is completely closed, it is improper to say that it is caused by horror vacui.
The wine has no mind to fear anything. Even if it had one, why would it fear that void which is nothing but a chimera?
The wine cannot leave the cask because:
- outside, everything is as full as it can be
- the wine cannot go down because that space is occupied by the air
- that air has nowhere to go in the universe unless one opens the top of the cask and let the air enter as to allow the wine to take its place
I do not want to make certain that there is no void at all in nature because:
- my discourse would become too long if I explained the whole universe
- my experiences of the universe not enough to prove it, although they are enough to persuade us that the spaces where we sense nothing are filled with the same aether, and contain at least as much of that aether, as those occupied by the bodies that we sense.
Thus, when a vessel is full of gold or lead, it has the same amount of aether than when it is empty.
This will be strange to those who only think that reality is limited to the world that they can touch. But when you have considered for a bit what makes us sense a body or not sense it, I am sure you will find nothing incredible in the above.
We cannot sense all the things around us. There are some things that we can sense sometimes, and some things that we can never sense.
- The heat of our heart is quite great. But we do not feel it because it is always there.
- The weight of our body is not small, but it does not discomfort us.
- We do not even feel the weight of our clothes because we are accustomed to wearing them.
We cannot sense any body unless it is the cause of some change in our sensory organs, i.e. An object moves which causes a subsequent movement in the aether that make up our organs.
The objects that are not always present can well do this if they have enough force. If they corrupt something by their action, that something can be repaired afterwards by nature, when they are no longer acting.
But if those sensory matter always affected the aether of our senses to the point that they separate them from sensing the aether, an ability that we had at the start of our life, then our senses will resist the sensing of the aether. This will cause us to lose that sense.
, and thus they can have left there only those that completely resist their action and by means of which they cannot be sensed in any way. –>
So it is no wonder that there are many spaces around us where we sense nothing, even if there is the aether.
The Bodies Within the Aether
A drop of water that evaporates takes up more space than that occupied by the droplet because of the in-between space. It follows that the aether has a lot of in-between spaces.
But, because the in-between spaces in the aether cannot be void, it means that such aethereal spaces are filled up with other bodies.