If Ricardo and Mill had contented themselves with laying down what the amount of rent was, governed by the quality of the soil's fertility and by the forces which they feebly recognised by the word situation, no harm would have been done. They would have given a tolerably fair description of the causes on which the magnitude of rent depends. It would not indeed have explained what rent is, but it would have expressed truths with which the common agricultural mind was familiar, and they might have retained the command of agricultural ears. But scientific ambition would not be satisfied with so simple and unpretending a statement. It was resolved that the explanation of rent should take the shape of a scientific doctrine; and with this object it invented an addition to it of whose scientific character there could be no doubt. "It converted the land," in the words of Mr. Mill, "which yields least return to the labour and capital employed on it, and gives only the ordinary profit of capital, without leaving anything for rent, into a standard for estimating the amount of rent which will be yielded by all other land. Any land yields as much more than the ordinary profits of stock, as it yields more than what is returned by the worst land in cultivation." This worst land, which had no rent to give, was erected into a standard which should measure rents as accurately as a yard measures distances, and a pound avoirdupois weights. Most useful indeed is the yard which tells us how far it is to Dover, and the lb. weight which informs us how heavy the load of coals is which has reached our door; and delightful truly, would be an instrument which should tell a disputing landlord and tenants, with unerring precision, how much rent exactly each farm was bound to pay. But this "margin of calculation," this land which pays no rent--what landlord or what farmer has ever inquired for it in the calculation of their rents? Has it ever occurred to the thoughts, or passed the lips, of a single practical agriculturist, in these days of excitement, and anger, and unceasing declamations in the press and tribune on rent? And if it had been found, what possible help could it have brought to a single agriculturist? Such land could be no measure to measure by. A measure must either be a given portion of the thing measured, as a yard of length, or else be an effect of a given force, as the height of the barometer of the pressure of the atmosphere. A piece of land which yields no rent cannot measure one that does, because the non-payment of rent is not the effect of a single force but of many diverse ones. A particular farm may pay no rent because it is isolated by want of roads, or is in a lonely spot, or is far off from manures, or is burdened with excess of taxation, as a whole parish in Buckinghamshire which was said to have gone out of cultivation because no man would face the burden of its poor-rates. What facility for calculation could such a parish furnish to a farmer