With reference to these distant galaxies of apparently complete solar systems like our own, the same principles must regulate the conversion of this energy of planetary electricity into the energy of solar light and heat as we see manifested in our own sun. The light of the individual stars is sufficient evidence of this; but the question may be asked, Is the electrical interaction between separate galaxies and between different solar systems in the same galaxy universal, or are these operations merely local? In other words, Is the source and the mode of solar energy in accordance with a single universal law of and between all created universes, or is it limited in effective energy to the members of each individual solar system alone? The answer is, that it is not less universal than the law of gravitation and no more so. There is a prevalent popular fallacy that the force of gravity is such that the movements, not only of solar systems, but of whole galaxies, and of all the illimitable systems of galaxies, are under its effective control, and that the whole universe of boundless space acknowledges its overwhelming sway. But nothing can be further from the truth. We know, of course, that the law is universal, as expressed in the statement of its terms by Newton, but the mere statement of the law itself, as applied to interstellar distances, refutes the idea that solar systems and galaxies can rotate around any common center by virtue of the attraction of gravitation as a controlling force. The universality of the law itself has even been doubted. Professor Ball says, "In the first book about astronomy which I read in my boyhood there was a glowing description.... I allude to the discovery, or the alleged discovery, of a certain 'central sun' about which it was believed or stated that all the bodies in the universe revolved.... It was too good to be true. No one ever hears anything about the central sun hypothesis nowadays.... It must be, then, admitted that when the law of gravitation is spoken of as being universal, we are using language infinitely more general than the facts absolutely warrant. At the present moment we only know that gravitation exists to a very small extent in a certain indefinite small portion of space. Our knowledge would have to be enormously increased before we could assert that gravitation was in operation throughout this very limited region; and even when we have proved this, we should only have made an infinitesimal advance to a proof that gravitation is absolutely universal."