Original text - Engels - The Deryaguin approximation

when dealing with interactions between macrobodies,it is often the case that the range of the interaction is such that the two bodies do not interact significantly until the distance of closest approach is small compared to the radii of cuvarture of the bodies.Under these circumtances,a very useful approximate expression for theinteraction energy per unit area of plane parallel half-spaces.The approximation is due,originally,to Deryaguin(1934)