 Kohler theory is at the heart of cloud micro physics. It deals with two competing processes. One raises the equilibrium saturation vapor pressure above the Clausius-Clapeyron saturation vapor pressure of a flat surface of pure water. This is called the Kelvin effect, or the curvature effect. In the second process lowers the equilibrium vapor pressure. This is called Reo's law or the solute effect. For view of the previous two sections of this lesson, you have forgotten these two effects. We can approximate the curvature effect as a constant over the drop radius, and we can approximate the solute effect as the negative of a constant over the drop radius cubed. Together they give us super saturation for a drop. How do these two give us the Kohler curve? The curvature effect goes as the positive inverse of the radius. The solute effect goes as the inverse of the radius cubed and is negative, and at small r it is greater negative than the curvature effect is positive. As the drop gets bigger, then the curvature effect becomes more important, and then the drop equilibrium super saturation follows the curvature effect. Note that each drop has its own Kohler curve. The super saturation of the environment, which can be positive by radiative cooling, mixing radiobatic ascent, determines what will happen to the drop.