Thus from the principle of the conservation of energy, which is in operation not only in our planetary world, but throughout the whole of the solar and stellar space, and indeed throughout the whole universe, we arrive at the conclusion that the total quantity of energy throughout the universe is unchangeable. In the evolution and development of worlds, and in the destruction of those worlds after long periods of time, throughout all the varied manifestations of heat, light, electricity, and magnetism, associated with the development and destruction of each globe, the sum-total of the energy of the universe remains the same. Meteors may rush into the atmosphere of planets, and be dissolved into Aether through the friction, comets may be dissolved into their component gases as they near the sun, water may be changed into vapour by the heat of the summer sun, vegetation may be produced from apparently dead matter, and then that vegetation may itself decay and return to the dust by which it had been built up, but throughout all these processes of birth and death, of evolution and devolution, the sum-total of active living energy which is associated with all the phenomena, remains unalterable and unchangeable. Such is the teaching of the great principle of the Conservation of Energy as enunciated by Mayer and Helmholtz. ART. 53. _Transformation of Energy._--One of the chief characteristics of energy is, that we can transform it, and it is chiefly of use to us because of its capability to be transformed, but in all its transformations, the total quantity of energy remains the same. The transformation of energy renders it necessary to the existence of all life, and to all physical change in the universe. Mayer showed us that all energy in the solar system primarily derives its existence from the sun, and that all plant life and physical life owe their continued existence to the energy which is poured out from the sun upon the planetary worlds. So that energy is always flowing from the sun into the surrounding space in the form of light, heat, and electricity, the medium of its passage being the universal Aether. This principle of transformation teaches us, that heat may be converted into electricity; that light may be converted into heat, or electricity may be converted into either heat or light or both. This principle of transformation naturally follows from the principle of the conservation of energy; because, if energy cannot be destroyed in any way, but is made to disappear by any process, it must reappear in some other form, and therefore has been transformed from its original state. So that, whenever one kind of energy disappears, then it is absolutely necessary, according to the principle of conservation of energy, that some other kind shall be produced. There cannot be any real loss or destruction.