A little more on Marshall. Marshall's explanation of adjustment to
equilibrium in a competitive market has firms adjusting output until demand
price equals supply price. As opposed to Walras' conception of a auction
market where price adjustments lead to changes in the quantities demanded
and supplied. This does not make a difference if the demand and supply
curves have the normal slopes, but it does matter to the stability of
various equilibria if the demand curve slopes up or the supply curve down.
Malcolm Rutherford