; but no one has seen a single
molecule or a single electron, yet the characters of events are only
explicable to us by expressing them in terms of these scientific
objects. Undoubtedly molecules and electrons are abstractions. But then
so is Cleopatra's Needle. The concrete facts are the events
themselves--I have already explained to you that to be an abstraction
does not mean that an entity is nothing. It merely means that its
existence is only one factor of a more concrete element of nature. So an
electron is abstract because you cannot wipe out the whole structure of
events and yet retain the electron in existence. In the same way the
grin on the cat is abstract; and the molecule is really in the event in
the same sense as the grin is really on the cat's face. Now the more
ultimate sciences such as Chemistry or Physics cannot express their
ultimate laws in terms of such vague objects as the sun, the earth,
Cleopatra's Needle, or a human body. Such objects more properly belong
to Astronomy, to Geology, to Engineering, to Archaeology, or to Biology.
Chemistry and Physics only deal with them as exhibiting statistical
complexes of the effects of their more intimate laws. In a certain
sense, they only enter into Physics and Chemistry as technological
applications. The reason is that they are too vague. Where does
Cleopatra's Needle begin and where does it end? Is the soot part of it?
Is it a different object when it sheds a molecule or when its surface
enters into chemical combination with the acid of a London fog? The
definiteness and permanence of the Needle is nothing to the possible
permanent definiteness of a molecule as conceived by science, and the
permanent definiteness of a molecule in its turn yields to that of an
electron. Thus science in its most ultimate formulation of law seeks
objects with the most permanent definite simplicity of character and
expresses its final laws in terms of them.

Again when we seek definitely to express the relations of events which
arise from their spatio-temporal structure, we approximate to simplicity
by progressively diminishing the extent (both temporal and spatial) of
the events considered. For example, the event which is the life of the
chunk of nature which is the Needle during one minute has to the life of
nature within a passing barge during the same minute a very complex
spatio-temporal relation. But suppose we progressively diminish the time
considered to a second, to a