urposes of daily intercourse its emphasis is needless. What it
comes to is this: Amidst the structure of events which form the medium
within which the daily life of Londoners is passed we know how to
identify a certain stream of events which maintain permanence of
character, namely the character of being the situations of Cleopatra's
Needle. Day by day and hour by hour we can find a certain chunk in the
transitory life of nature and of that chunk we say, 'There is
Cleopatra's Needle.' If we define the Needle in a sufficiently abstract
manner we can say that it never changes. But a physicist who looks on
that part of the life of nature as a dance of electrons, will tell you
that daily it has lost some molecules and gained others, and even the
plain man can see that it gets dirtier and is occasionally washed. Thus
the question of change in the Needle is a mere matter of definition. The
more abstract your definition, the more permanent the Needle. But
whether your Needle change or be permanent, all you mean by stating that
it is situated on the Charing Cross Embankment, is that amid the
structure of events you know of a certain continuous limited stream of
events, such that any chunk of that stream, during any hour, or any day,
or any second, has the character of being the situation of Cleopatra's
Needle.

Finally, we come to the third statement, 'There are dark lines in the
Solar Spectrum.' This is a law of nature. But what does that mean? It
means merely this. If any event has the character of being an exhibition
of the solar spectrum under certain assigned circumstances, it will also
have the character of exhibiting dark lines in that spectrum.

This long discussion brings us to the final conclusion that the concrete
facts of nature are events exhibiting a certain structure in their
mutual relations and certain characters of their own. The aim of science
is to express the relations between their characters in terms of the
mutual structural relations between the events thus characterised. The
mutual structural relations between events are both spatial and
temporal. If you think of them as merely spatial you are omitting the
temporal element, and if you think of them as merely temporal you are
omitting the spatial element. Thus when you think of space alone, or of
time alone, you are dealing in abstractions, namely, you are leaving out
an essential element in the life of nature as known to you in the
experience of your s