Principles of Economics, first published in 1890, went through eight editions
and is considered the most important treatise of 19th century and beyond. It
gave some landmark concepts like consumer surplus, producer surplus, price
elasticity of demand, and the idea of three periods, viz. market period, short
period and long period. The concept of National Dividend given in the Principles
is not a mere academic toy, but a practical instrument of great power designed
for service in the concrete solution of social problems. Marshall's theoretic
discussion follows the lines of the mathematical treatment of Cournot and
others, more particularly in his discussion of the doctrines of value,