The formation of Newton's rings was satisfactorily explained by Young,
According to him, these circular rings are formed due to interference of light rays reflected from the upper and lower surfaces of the air film formed between the convex surface of a plano-convex lens and the glass plate. In Fig, the incident ray SF is divided into two coherent rays 1 and 2 by reflection from the upper and lower surfaces of the wedge shaped air film. The reflected rays Land 2 of contact. The effective path difference between the interfering rays in interfere and produce bright and dark circular ring around the point of contact.
