 Understanding the sense in which atomic elements are “in time” is important for grasping the manner in which Wolff’s atomic elements interact. Since atomic elements lack extension, the nature of atomic interaction is not spatial. It is not the case, for example, that Wolff’s simple substances influence one another by physical contact and repulsion. Instead, atomic elements as unextended points of force affect, and are responsive to, degrees of change by communicating with each other in time. The series of changes internal to a given atomic element are the result of its own power (or motor force) as well as the motor forces of other elements to which it is connected. Ultimately Wolff believes that it is the interacting forces of a multitude of simple substances that gives rise to our idea of an extended object. In particular, we perceive extended objects at the level of appearance insofar as there are unextended points of force interacting in time at the atomic level. Our confused perception of this temporal interaction results in the idea of an extended object. Similarly to Locke, Wolff believes that it is the primitive qualities of a composite that produce, or effect in us, the various ideas we have of its secondary qualities. Since all sensible properties are considered by Wolff to be secondary qualities, extension, or a composite’s extendedness, results from the primitive forces of a composite at the atomic level. The analogy that Wolff presents to help explain the phenomenal manifestation of extension involves a rapidly ringing bell (Cosm. §789; cf. Burns 1966: 52). According to Wolff, just as the impression we gain from a rapidly ringing bell is the sound of one prolonged peal, where the successive strikes of a bell’s clacker are perceived as one monomial sound, our impression of extension is likewise the result of many successively acting atomic forces that give rise to our confused perception of one continuous extended object.