 Other schools were more localized and less enduring than the Cameralists or Mercantilists. One of the first is the Salamanca school of mid-sixteenth-century Spain that included Luis de Molina, Martín de Azpilcueta, and Francisco Suárez (see Grice-Hutchinson 1978). Another school drew inspiration from the natural law theories of Hugo Grotius and Samuel Pufendorf, who had addressed the principles governing contractual obligations in general, and the complexities of property rights in particular (see Skinner 1999). Johan De Wit and Christiaan Huygens of the Dutch Golden age recorded important insights into commercial mathematics (see Daston 1988; Sylla 2003). The Political Arithmeticians of seventeenth-century England and Ireland, notably William Petty, Edmund Halley, and John Graunt, devised ingenious methods for measuring population, the money supply, and the movement of core prices (see Rusnock 1999). The Stadialists of eighteenth-century Scotland, namely Lord Kames, Adam Ferguson, and John Millar, offered a theory of economic development based on four stages, hunting and gathering, shepherding, cultivation, and commerce and trade that was partly adopted by Hume and Smith (see Wolloch 2011).