In the special case of the earth, which will be dealt with in some detail, it is the object of this work to show that its property of complete energy conservation is amply verified by terrestrial phenomena. The extension of the principle from the earth to the whole planetary system has been made on precisely the same grounds as Newton extended the observed phenomena to his famous generalisation with respect to gravitation. PART II PRINCIPLES OF INCEPTION 13. _Illustrative Secondary Processes_ In this part of the work, an attempt will be made to place before the reader some of the purely terrestrial and other evidential phenomena on which the conclusions of the preceding General Statement are founded. The complete and absolute verification of that Statement is obviously beyond experimental device. Bound, as we are, within the confines of one planet, and unable to communicate with the others, we can have no direct experimental acquaintance with really separate bodies (§ 5) in space. But, if from purely terrestrial experience we can have no direct proofs on such matters, we have strong evidential conclusions which cannot be gainsayed. If the same kind of energy operates throughout the solar system, the experimental knowledge of its properties gained in one field of research is valuable, and may be readily utilised in another. The phenomena which are available to us for study are, of course, simply the ordinary energy processes of the earth--those operations which in the foregoing Statement have been described as secondary energy processes. Their variety is infinite, and the author has accordingly selected merely a few typical examples to illustrate the salient points of the scheme. The energy acting in these secondary processes is, in every case, derived, either directly or indirectly, from the energy of rotation or axial energy of the earth. In themselves, the processes may be either energy transformations or energy transmissions or a combination of both these operations. When the action involves the bodily movement of material mass in space, the dynamical energy thus manifested, and which may be transmitted by the movement of this material, is termed mechanical or "work" energy (§ 31); when the energy active in the process is manifested as heat, chemical, or electrical energy, we apply to it the term "molecular" energy. The significance of these terms is readily seen. The operation of mechanical or "work" energy on a mass of material may readily proceed without any permanent alteration in the internal arrangement or general structure of that mass. Mechanical or "work" energy is dissociated from any molecular action. On the other hand, the application of such forms of energy as heat or electrical energy to material leads to distinctly molecular or internal effects, in which some alteration in the constitution of the body affected may ensue. Hence the use of the terms, which of course is completely arbitrary.