But the same circumstance, namely, the abundance and consequent cheapness of coals, from whatever cause it may arise, which would make it necessary to abandon those mines on which there was no rent, or a very moderate one, would, if there were the same abundance, and consequent cheapness of raw produce, render it necessary to abandon the cultivation of those lands for which either no rent was paid, or a very moderate one. If, for example, potatoes should become the general and common food of the people, as rice is in some countries, one fourth, or one half of the land now in cultivation, would probably be immediately abandoned; for if, as Adam Smith says, "an acre of potatoes will produce six thousand weight of solid nourishment, three times the quantity produced by the acre of wheat," there could not be for a considerable time such a multiplication of people, as to consume the quantity that might be raised on the land before employed for the cultivation of wheat; much land would consequently be abandoned, and rent would fall; and it would not be till the population had been doubled or trebled, that the same quantity of land could be in cultivation, and the rent paid for it as high as before. Neither would any greater proportion of the gross produce be paid to the landlord, whether it consisted of potatoes, which would feed three hundred people, or of wheat, which would feed only one hundred; because, though the expenses of production would be very much diminished if the labourer's wages were chiefly regulated by the price of potatoes and not by the price of wheat, and though therefore the proportion of the whole gross produce, after paying the labourers, would be greatly increased, yet no part of that additional proportion would go to rent, but the whole invariably to profits,--profits being at all times raised as wages fall, and lowered as wages rise. Whether wheat or potatoes were cultivated, rent would be governed by the same principle--it would be always equal to the difference between the quantities of produce obtained with equal capitals, either on the same land or on land of different qualities; and therefore, while lands of the same quality were cultivated, and there was no alteration in their relative fertility or advantages, rent would always bear the same proportion to the gross produce.