Page:An Enquiry Concerning the Principles of Natural Knowledge.djvu/113

 molecules, which are complex scientific objects. There is no such thing as a molecule at an instant. A molecule requires a minimum of duration in which to display its character. Similarly physical objects are steady complexes of molecules with an average permanence of character throughout certain minimum durations.

26.4 Thus the recognition which is involved in perception is the reason for the importance in physical science of Lorentz’s hierarchy of microscopic and macroscopic equations.

26.5 The further consideration of objects, in particular their instantaneous spatial positions and the quantitative distribution of material through space, is resumed in Part IV, after the theory of space and time has been established.