The law of the transformation of energy is "the enunciation of the empirical fact that in general any one form of energy may by suitable processes be transformed, wholly or in part, to an equivalent amount in any other given form." This law, however, is subject to limitations which are supplied by the dissipation of energy. "No known natural process is exactly reversible, and whenever an attempt is made to transform and retransform energy by an imperfect process, part of the energy is necessarily transformed into heat and _dissipated_, so as to be incapable of further useful transformation. It therefore follows that, as energy is constantly in a state of transformation, there is a constant _degradation_ of energy to the final unavailable form of uniformly diffused heat, and that will go on until the whole energy of the universe has taken this final form."[264] No mechanical work can be done by heat in a state of equilibrium; as a dynamical agent it is _dead_. "Thus the inexorable laws of mechanics indicate that the store of force in our planetary system, which can only suffer loss and not gain, must be finally exhausted."[265] So far, then, as the conservation of energy has any scientific meaning, it is inadequate to account for the origin or explain the continuance of the existing order of nature. It is true we may conceive that every atom of matter was endowed at the Creation with a certain store of potential energy--"the potential energy of gravitation"[266]--which it has ever since given out; but as every motion which has resulted from its action has been attended with the expenditure of a certain amount of the original endowment, it must have been continually undergoing a diminution. There is, says Professor Norton, no escaping this conclusion but by taking the ground that _the primary atomic forces_ (as gravitation, and the atomic repulsion and attraction by which atoms are aggregated into bodies of sensible magnitude) are correlated with the _living forces_ (or various forms of energy) which are involved in the motions that have resulted from the previous operation of the primary atomic forces. "But," he says, "_no evidence has been obtained of any such correlation_." The primary force of attraction (if it be regarded as a primary force) may be the cause of motion in bodies which are separated in space, and part of that energy of motion may be transformed into the energy of heat or light or electricity, but the primary force of attraction is not transformed. Energy is convertible into other forms of energy, but heat, light, and electricity are not transformable into primary force. The correlation of force and energy is therefore a scientific heresy.[267]