The nebular hypothesis above described has recently [we are told][13] been strongly confirmed and enlarged by the theory that this cosmogonic process did not simply take place once, but is periodically repeated. While new cosmic bodies arise and develop, out of rotating masses of nebula in some parts of the universe, in other parts old, extinct, frigid suns come into collision, and are once more reduced by the heat generated to the condition of nebulæ. It appears, in fact, to be assumed that this cyclic process has been actually demonstrated, for we are told[14] that astronomy reveals, in the endless depths of space, "Millions of circling spheres, larger than our earth, and, like it, in an eternal rhythm of life and death." Moreover, "life" is here to be understood literally, for it is a cardinal article of such evolutionary belief that equally with the foundation of cosmic bodies and the separation of planets, the production of organic life, of plants and animals, has been wrought by forces which the material universe contains within itself,[15] and accordingly,[16] We now definitely know that the organic world on our earth has been continuously developed "in accordance with eternal iron laws." ... An unbroken series of natural events, following an orderly course of evolution according to fixed laws, now leads the reflecting human spirit through long aeons from a primeval chaos to the present order of the cosmos. Finally, at the back of all these processes, we are to recognize the one ultimate reality, the universe itself, which originates and undergoes all these evolutions. In its regard Professor Haeckel tells us[17] that, The universe, or cosmos, is eternal, infinite, and illimitable. Its substance, with its two attributes (matter and energy) fills infinite space and is in eternal motion. This motion runs on through infinite time as an unbroken development, with a periodic change from life to death, from evolution to devolution.... And again:[18] The two fundamental forms of substances, ponderable matter and ether, are not dead and moved only by extrinsic force, but they are endowed also with sensation and will (though naturally of the lowest grade); they experience an inclination for condensation, a dislike of strain; they strive after the one and struggle against the other. Moreover, Movement[19] is as innate and original a property of substances as is sensation. Such is the raw material whose metamorphoses produce, or rather constitute, all possible worlds, while paramount over every thing dominates the "Law of Substance," under which title Professor Haeckel unites the scientific principles of the indestructibility of matter, and the conservation of energy. Thus is the conclusion reached,[20]