section_path: Graphical representations/History of the curves
section_name: History of the curves
paragraph_text: History of the curves
  
  Since supply and demand can be considered as functions of price they have a natural graphical representation. Demand curves were first drawn by Augustin Cournot in his Recherches sur les Principes Mathématiques de la Théorie des Richesses (1838) – see Cournot competition. Supply curves were added by Fleeming Jenkin in The Graphical Representation of the Laws of Supply and Demand... of 1870. Both sorts of curve were popularised by Alfred Marshall who, in his Principles of Economics (1890), chose to represent price – normally the independent variable – by the vertical axis; a practice which remains common.
  
  If supply or demand is a function of other variables besides price, it may be represented by a family of curves (with a change in the other variables constituting a shift between curves) or by a surface in a higher dimensional space.