These event-particles are the instantaneous facts which pass with the instantaneous moment.

What is really traversed are other event-particles which at succeeding instants occupy the same points of space {alpha} as those occupied by the event-particles of the rect {rho}.

For example, we see a stretch of road and a lorry moving along it.

The instantaneously seen road is a portion of the rect {rho}--of course only an approximation to it.

The lorry is the moving object.