Editing Supply and demand (section)

===History of the curves===
{{multiple image
 | width1 = 200
 | width2 = 360
 | width3 = 200
 | align = center
 | footer = Figure 2. Early supply and demand curves
 | image1 = Cournotdemand.gif
 | caption1 = Cournot's ''Recherches'' (1838)
 | image2 = Jenkincurves.gif
 | caption2 = Jenkin's ''Graphical Representation'' (1870)
 | image3 = Marshalldemand.gif
 | caption3 = Marshall's ''Principles'' (1890)
}}
Since supply and demand can be considered as [[function (mathematics)|functions]] of price they have a natural graphical representation. Demand curves were first drawn by [[Augustin Cournot]] in his {{lang|fr|Recherches sur les Principes Mathématiques de la Théorie des Richesses}} (1838){{snd}}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 (Marshall book)|Principles of Economics]]'' (1890), chose to represent price{{snd}}normally the independent variable{{snd}}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.