A far better phrase to express this equivalence of force has been suggested and used by several writers in what is called the "Transmutation of Force." For there is no correlation, or reciprocal relation, between heat as originally produced by the consumption of fuel and the force as engendered in steam before it is transmuted into work. Nor is there any real equivalence as between the two forces after its transmutation. A very large per centage of heat is lost in its transmutation from a latent form in fuel to an active or available form in steam, and a still greater loss in its transmission into work by machinery. Theoretically, there may be such an equivalence as that named, but practically it is impossible to realize it. And a theory that is impossible of realization is of no practical utility in itself, and of little value as the basis of further theory. If, then, the theory of force equivalence is a failure in practical application, it furnishes a very poor basis on which to predicate force-correlation, or the doctrine of reciprocal forces. It is estimated, for instance, that a pound weight falling seven hundred and seventy-two feet, will, in striking the earth, impart to it a degree of heat equivalent to raising one pound of water 1° F. But the heat thus imparted can never be so utilized as to raise a pound weight seven hundred and seventy-two feet into the air. This shows that there is no actual reciprocity of relationship between the force as originally engendered and finally expended in work. Nor can it be shown that the original force is transmuted or changed into another and different kind of force by the operation. The force generated and the force expended are essentially one and the same, as much so as that transmitted from the power to the weight by means of a rope and pulley. And the quality of the force is not changed, whether the weight be lifted by machinery or the human hand. Force, in its mechanical sense, is that power which produces motion, or an alteration in the direction of motion, and is incapable of being specialized, except in a highly figurative sense, into a thousand and one correlates of motion. But these miscellaneous and figurative forces are not what we are considering. The doctrine of force-correlation takes no such wide and comprehensive sweep. It embraces neither the force of wit, nor the force of folly; but mechanical force and its equivalents. The force exercised by the human hand in lifting a weight either with or without rope and pulley is, in every definitional sense of the word, mechanical force. For the arm and hand are only the implements, or mechanical contrivances of nature, by which the will-power transmutes itself into work, or, more properly speaking, transmits itself from the point of force-generation to that of force-expenditure. And this is precisely the office performed by all mechanical contrivances for the transmission--not transmutation--of force.