And the remedy was plain: the net product of agriculture must somehow be made to rise instead of fall. They supported their contention with a certain erroneous theory that agriculture is the sole source of wealth, but the error made little practical difference to the argument, for agriculture is always a sufficiently important source of wealth to make its improvement a national concern. How then was the net product to be increased? By better methods of cultivation, by removal of legal and official interferences, and by lightening the public burdens through the abolition of all existing taxes and of the existing system of collecting them through farmers-general, and the institution instead of a single tax on the net product of the soil, to be collected directly by responsible officials. According to the reminiscences of strangers who happened to fall into their company, the talk of the economists always ran much on the net product and the single tax, for they believed the two great needs of the country were agricultural improvement and financial reform. When Quesnay was offered a farmer-generalship of the taxes for his son, he said, "No; let the welfare of my children be bound up with the public prosperity," and made his son a farmer of the land instead. In Quesnay's rooms in the palace of Versailles Smith would sometimes hear words that would sound very strange in the house of the king. Mercier de la Riviere, Quesnay's favourite disciple, while writing his book on the _Natural and Essential Order of Political Societies_, published in 1767, almost lived in Quesnay's apartments, discussing the work point by point with the master. The Marquis de Mirabeau mentions having seen him there six whole weeks running, "moulding and remoulding his work, and consequently denying father and mother" for the time. One day Madame du Hausset heard a memorable conversation there between these two economists. "This kingdom," observed Mirabeau, "is in a miserable state. There is neither energy in the nation nor money to serve in its place." "No," replied Mercier de la Riviere, counsellor of the Parliament of Paris and late Governor of Martinico, "it cannot be regenerated except by a conquest like that of China, or by a great internal convulsion; but woe to those who will be there then, for the French people does nothing by halves." The words made the little lady-in-waiting tremble, and she hurried out of the room; but M. de Marigny, brother of the king's mistress, who was also present, followed her, and bade her have no fear, for these were honest men, if a little chimerical, and they were even, he thought, on the right road, though they knew not when to stop and went past the goal.[182]