as much as of the very latest experimental results
which have led to its production.

To put ourselves in the position to assimilate and to criticise any
change in ultimate scientific conceptions we must begin at the
beginning. So you must bear with me if I commence by making some simple
and obvious reflections. Let us consider three statements, (i)
'Yesterday a man was run over on the Chelsea Embankment,' (ii)
'Cleopatra's Needle is on the Charing Cross Embankment,' and (iii)
'There are dark lines in the Solar Spectrum.' The first statement about
the accident to the man is about what we may term an 'occurrence,' a
'happening,' or an 'event.' I will use the term 'event' because it is
the shortest. In order to specify an observed event, the place, the
time, and character of the event are necessary. In specifying the place
and the time you are really stating the relation of the assigned event
to the general structure of other observed events. For example, the man
was run over between your tea and your dinner and adjacently to a
passing barge in the river and the traffic in the Strand. The point
which I want to make is this: Nature is known to us in our experience as
a complex of passing events. In this complex we discern definite mutual
relations between component events, which we may call their relative
positions, and these positions we express partly in terms of space and
partly in terms of time. Also in addition to its mere relative position
to other events, each particular event has its own peculiar character.
In other words, nature is a structure of events and each event has its
position in this structure and its own peculiar character or quality.

Let us now examine the other two statements in the light of this general
principle as to the meaning of nature. Take the second statement,
'Cleopatra's Needle is on the Charing Cross Embankment.' At first sight
we should hardly call this an event. It seems to lack the element of
time or transitoriness. But does it? If an angel had made the remark
some hundreds of millions of years ago, the earth was not in existence,
twenty millions of years ago there was no Thames, eighty years ago there
was no Thames Embankment, and when I was a small boy Cleopatra's Needle
was not there. And now that it is there, we none of us expect it to be
eternal. The static timeless element in the relation of Cleopatra's
Needle to the Embankment is a pure illusion generated by the fact that
for p