“ Petty is much concerned to discover a fixed unit of value, and he thinks he has found it in the necessary sustenance of a man for a day. He understands the cheapening effect of the division of labour. ”

“ He states correctly the notion of "natural and true" rent as the remainder of the produce of land after payment of the cost of production, but he seems to have no idea of the "law of diminishing returns." He has much that is just on the subject of money: he sees that there may be an excess of it as well as a deficiency, and regards the prohibition of its exportation as contrary to sound policy. ”

“ He gained some notoriety in 1650 by restoring to life a woman who had been hanged for infanticide. In 1651 he was made professor of anatomy at Oxford, and also became professor of music at Gresham College. In 1652 he went to Ireland, having been appointed physician to the army in that country. In 1654, observing that the admeasurement and division of the lands forfeited in 1641 and granted to the soldiers had been "most inefficiently and absurdly managed," he entered into a contract to execute a fresh survey, which he completed in thirteen months. ”