The theory of plane discontinuities developed in Part I is applied to a “window” and change of cross section in tubes of both circular and rectangular cross section. In the case of the rectangular tube conformal mapping is introduced as an alternative approach to the problem. Reflection and transmission coefficients are determined from the equivalent circuit of Part I, and the theory is also applied to the analysis of certain types of cavity resonators. Finally, the experimental determination of equivalent circuit impedances is discussed.