, . . . . . . . . (Lang, 1967), , , : , , , , , . , . (Lindley, 1937; Raman, Rendal, 1944; Ramachandran, 1946; , 1955; Slawson, Denning, 1955; , , 1958; Denning, 1961; Tolansky, 1966; Seal, 1966; Lang, 1967). . . (1968).