This chapter describes how water interacts with the solid system of the soil. This chapter explains surface tension, or more specifically, the surface tension coefficient. Laplace's surface tension theory is presented. An equation is given and proved for the rise of a liquid in a capillary tube. The proof requires the use of the surface tension coefficient. The importance of surface tension is illustrated by giving examples of it in nature. Rise and fall of water in soil pores is examined using knowledge of water in a capillary tube. Hysteresis, which results from differential amounts of water being held in soil if the water is rising in the soil from a water table or if the water is falling from the surface through the soil, is explained, and the explanation is based on rise and fall of water in capillary tubes. A biography of Laplace is given in the appendix.