Excerpt from Notes on Magneto-Hydrodynamics, Vol. 4: Ohm's Law Next, let us consider a two-fluid theory. The simplest such theory involves two mass-conservation equations, while retaining a single momentum and a single energy equation for the total fluid. We assume that a single equation of state involving energy, pressure, and both densities is given. Counting variables, compared to the one-fluid theory, we have an extra density (matched by an extra mass conservation equation) and also an extra velocity vector, e.g., the difference or diffusion velocity. In ordinary fluid dynamics, this extra velocity is taken care of by supplementing the system of conservation equations by a diffusion relation, e.g., an assertion that the difference velocity is proportional to the concentration gradient. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.