Let a sluggish load of capacity Co be driven by a source of internal resistance Ro via an intermediate two-terminal pair. And let F12 denote the voltoge transmission fun-ction. The integral is indicated to have an interpretation as anindex of grade of performance of the transmission system matter not in frequency domain or in time domain senses. The author obtained through time domain artifice the power gain integral theorem formulated thus:Where W（∞） stands for the total stored energy in the complete system at t=∞ after being kicked across Co by a unit impulse current introduced at t = 0

and Ri for the ith resistance in the inserted network with impulse response current ii （t） flowing in it.The integral will assume its maximum value when the intermediate network is all reactive and satisfying certain guite weak limitations such that W（∞） = 0. Hence it is concluded that transmission models under said limitations will behave with performance of transmission invariant of circuit structure and parameters of the intermediate network. It is also concluded that confining the pass band of F12 in narrow interval may result in greater than unity gain with the system being inert.The paper also points out that the usual desposition of loading transmission circuit in resistive termination for"matching" considerations should receive a con when the circuit is to work for wide band purposes; for example

delay lines never should be loaded with resistance（as the situation may tolerate） aside from unavoidable stray capacitance.