other not.
    The first law was not fully understood until the second law was formulated by Clausius and Thomson in the 1850's. Some twenty-five years earlier Carnot had observed that like the fall of a stream that turns a mill wheel, it was the "fall" of heat from higher to lower temperatures that motivates a steam engine. That this work showed an irreversible destruction of "motive force" or potential for producing change suggested to Clausius and Thomson that either the first law was false (energy was not conserved), or else energy was not the motive force for change. Recognizing that the active principle and the conserved quantity could not be the same they realized that there were two laws at work and showed their relation. Clausius coined the word "entropy" to refer to the dissipated potential, and the second law states that all natural processes proceed so as to maximize the entropy (or equivalently minimize or dissipate the potential), while energy, at the same time is entirely conserved. The balance equation of the second law, expressed as

says that in all real world processes entropy always increases (literally "the change in entropy is greater than zero").
    In Clausius' (1865, p. 400) words, the two laws thus became: "The energy of the world remains constant. The entropy of the world strives to a maximum," and with this understanding, in sharp contrast to the "dead" mechanical world of Descartes and Newton, the nomological basis for a world that is instead active, and end-directed was identified. Entropy maximization as Planck first recognized provides a final cause, in Aristotle's typology, of all natural processes, "the end to which everything strives and which everything serves" or "the end of every motive or generative process" (Bunge, 1979, p. 32).
    The active nature of the second law is intuitively easy to grasp and empirically easy to demonstrate. Figure 2 shows a glass of hot liquid placed in a room at a cooler temperature.The difference in temperatures

Figure 2. A glass of liquid at temperature T(I) is placed in a room at temperature T(II) so that T(I) is greater than T(II). The disequilibrium produces a field potential that spontaneously drives a flow of energy in the form of heat from the glass to the room so as to drain the potential until it is minimized (the entropy is maximized), at which time thermodynamic equilibrium is reached and all flows stop. The expression refers to the conservation of energy in that the flow from the glass equals the flow of heat into the room. From Swenson (1991), p. 45. Copyright 1991 Intersystems Publications. Adapted by permission.

in the glass-room system constitutes a potential and a flow of energy in the form of heat, a "drain" on the potential, is produced from the glass (source) to the room (sink) until the potential is minimized (the entropy is maximized) and the liquid and the room are at the same temperature. At this point, all flows and thus all entropy production stops

and the system is at thermodynamic equilibrium.
The same principle applies to any system where any form of energy is out of equilibrium with its surrounds (e.g., whether mechanical, chemical, electrical or energy in the form of heat), a potential exists that the