The recognition of the indestructibility of energy seemed to accentuate the difficulties of the cosmogonic problems. The theses of Mayer and of Helmholtz, on the manner in which the Sun replenishes its losses of heat, have had to be abandoned. My explanation is based upon chemical reactions in the interior of the Sun in accordance with the second law of thermodynamics. The theory of the “degradation” of energy appeared to introduce a still greater difficulty. That theory seems to lead to the inevitable conclusion that the Universe is tending towards the state which Clausius has designated as “_Wärme Tod_” (heat death), when all the energy of the Universe will uniformly be distributed through space in the shape of movements of the smallest particles. That would imply an absolutely inconceivable end of the development of the Universe. The way out of this difficulty which I propose comes to this: the energy is “degraded” in bodies which are in the solar state, and the energy is “elevated,” raised to a higher level, in bodies which are in the nebular state. Finally, I wish to touch upon one cosmogonical question which has recently become more actual than it used to be. Some kind of “spontaneous generation,” origination of life from inorganic matter, had been acquiesced in. But just as the dreams of a spontaneous generation of energy—_i.e._, of a _perpetuum mobile_—have been dispelled by the negative results of all experiments in that direction, just in the same way we shall have to give up the idea of a spontaneous generation of life after all the repeated disappointments in this field of investigation. As Helmholtz[2] says, in his popular lecture on the growth of the planetary system (1871): “It seems to me a perfectly just scientific procedure, if we, after the failure of all our attempts to produce organisms from lifeless matter, put the question, whether life has had a beginning at all, or whether it is not as old as matter, and whether seeds have not been carried from one planet to another and have developed everywhere where they have fallen on a fertile soil.” [Footnote 2: Helmholtz, _Populäré Wissenschaftliche Vorträge_. Braunschweig, 1876, vol. iii., p. 101.] This hypothesis is called the hypothesis of panspermia, which I have modified by combining it with the thesis of the radiation pressure. My guiding principle in this exposition of cosmogonic problems has been the conviction that the Universe in its essence has always been what it is now. Matter, energy, and life have only varied as to shape and position in space. THE AUTHOR. STOCKHOLM, December, 1907. WORLDS IN THE MAKING I VOLCANIC PHENOMENA AND EARTHQUAKES The Interior of the Earth