But a physical object is a condition for the occurrence of sense-objects other than those which are its components.

For example, the atmosphere causes the events which are its situations to be active conditioning events in the transmission of sound.

A mirror which is itself a physical object is an active condition for the situation of a patch of colour behind it, due to the reflection of light in it.
Thus the origin of scientific knowledge is the endeavour to express in terms of physical objects the various _roles_ of events as active conditions in the ingression of sense-objects into nature.

It is in the progress of this investigation that scientific objects emerge.

They embody those aspects of the character of the situations of the physical objects which are most permanent and are expressible without reference to a multiple relation including a percipient event.