That heat is amode of motion does not signify that heat and cold as qualitatively experienced are "unreal," but that the qualitative experience can be treated as an event measured in terms of units of velocity of movement, involving units of position and time, so that it can be connected with other events or changes simi- larly formulated. The test of the validity of any particular intellectual conception, measurement or enumeration is func- tional, its use in making possible the institution of interactions which yield results in control of actual experiences of observed objects.