A KINETIC THEORY OF GASES AND LIQUIDS by RICHARD D. KLEEMAN. Originally published in 1920. PREFACE: THE object of writing this book is to formulate a Kinetic Theory of certain properties of matter, which shall apply equally well to matter in any state. The desirability of such a development need not be emphasized. The difficulty hitherto experienced in applying the results obtained in the case of the Kinetic Theory of Gases in the well-known form to liquids and intermediary states of matter has been pri marily due to the difficulty of properly interpretating molec ular interaction. In the case of gases this difficulty is in most part overcome by the introduction of the assumption that a molecule consists of a perfectly elastic sphere not surrounded by any field of force. But since such a state of affairs does not exist, the results obtained in the case of gases hold only in a general way, and the numerical constants involved are therefore of an indefinite nature, while in the case of dense gases and liquids this procedure does not lead to anything that is of use in explaining the facts. Instead of an atom, or molecule, consisting of a per fectly elastic sphere, it is more likely that each may be regarded simply as a center of forces of attraction and repulsion. If the exact nature of the field of force sur rounding atoms and molecules were known, it would be a definite mathematical problem to determine the resulting properties of matter. But our knowledge in this connection is at present not sufficiently extensive to permit a develop ment of the subject along these lines. But in whatever way the subject is developed fundamental progress will have been made only if molecular interaction is not, as is usually the case, represented by the collision of elastic spheres. It will be shown in this book that the subject may be developed to a considerable extent along sound mathe matical lines yielding important results without knowing the exact nature and immediate result @FÂ?(ö ¾Û€