The increased concern for sustainable development in recent years has spurred renewed interest in the concept of economic income. In this paper, we attempt to provide a modern version of the concept defined by Fisher, Lindahl and Hicks based on a multi-sector optimal growth model. In paricular, we show that the the linearized Hamiltonian as a comprehensive net national product measure is indeed the return to capital when the linearization is conducted with respected to the right variables. This is in line with the conjecture by Solow in his keynote speech at the 40th anniversary of the Resources for the Future.