The writings of William Thornton are central to the history of the "Laws of Supply and Demand" and seminal in understanding the rise of neoclassical economics. Thornton has previously been cast as a minor player in John Stuart Mill's recantation of the wages fund doctrine. This event is discussed by Schumpeter in "A History of Economic Analysis" and Samuel Hollander in "The Economics of John Stuart Mill". This new edition should show how he played a major role in the history of economic thought. His first edition of "On Labour" was a critique of the laws of supply and demand and served to mobilize the major players in the burgeoning neo-classical movement - Jevrons, Edgeworth, Jenkin and Marshall - to reply with mathematical responses to the debate.