The expressions "physical," and "mental," as applied to science, have hitherto been employed to designate those branches of knowledge of which physical and mental phenomena respectively form the subject-matter. Thus, Chemistry is considered as a physical science because the subject-matter on which chemical inquiry is exercised, viz., external nature, is physical. Psychology, on the other hand, is a mental science; the subject-matter of it being mental states and feelings. And as the office of the chemist consists in observing and analyzing material objects with a view to discovering the laws of their elementary constitution ; so, that of the psychologist consists in endeavouring, by means of reflection on what passes in his own mind, to ascertain the laws by which the phenomena of our mental constitution succeed and produce each other. If this be a correct statement of the principle on which the designations "mental" and "physical" are applied to the sciences, it seems to follow that Political Economy does not find a place under either category. Neither mental nor physical nature forms the subject-matter of the investigations of the political economist. He does not consider the laws according to which physical phenomena take place, nor yet those according to which mental phenomena take place. The subject-matter of his science is wealth, which is neither a purely physical nor a purely mental object, but possesses a complex character, equally derived from both departments of nature, and the laws of which are neither mental nor physical laws, though they are

dependent, and as I maintain, dependent equally on the laws of matter and on those of mind.

Let us consider, for example, the causes which determine the rate of wages. This, it will be admitted on all hands, is an economic problem. It is evident that the objects which the labourer receives are material objects, but those material objects are invested by the mind with a peculiar attribute in consequence of which they are considered as possessing value; and it is in their complex character, as physical objects invested with the attribute of value, that the political economist considers them. The subject-matter, therefore of the wages-problem possesses qualities derived alike from physical and from mental nature; consequently, if it is to be denominated from the nature of its subject-matter, it is equally entitled or disentitled to the character of a physical or mental problem.

But it is said that Political Economy considers the problem no further than as it depends on the action of the human mind. The food and clothing which the labourer consumes have, no doubt, physical properties, as the labourer himself has a physical as well as a mental nature; but with the physical properties, we are told, the political economist has no concern : he considers those objects so far forth only as they possess value, and value is a purely mental conception. But is this true? Does the political economist -does Mr. Senior, e. g., in his purely scientific treatment of this question— entirely put out of consideration the physical properties of the commodities which

the labourer consumes, or the physiological conditions on which the increase of the labouring population depends? What is the solution of the wages-problem? Wages, it will be said, depend on demand and supply; or, more explicitly, on the relation between the amount of capital applied to the payment of wages, and the number of labourers seeking employment. But the amount of capital employed in the payment of wages depends, amongst other causes, on the productiveness of industry in raising the commodities of the labourer's consumption—a circumstance which is equally dependent on the laws of physical nature as on the mental qualities which the workman brings to his task. The number of labourers seeking employment, again, depends, amongst other causes, on the laws of population; while these are determined as much by the physiological laws of the body, as the psychological laws of the mind; the political economist taking equal cognizance of both.

It thus appears that, as the subject-matter of Political Economy, viz., wealth, possesses qualities derived equally from the world of matter as from that of mind, so its premises are equally drawn from both these departments of nature. The latter point, indeed, is admitted by those economists who nevertheless, by what appears to me to be a strange oversight, represent the science as investigating the laws of wealth no further than as they depend on the laws of the human mind.

But perhaps this point will be made more clear—

the equal dependence, namely, of the science of Political Economy on the laws of the physical world and on those of the human mind-if we consider that a change in the character of the former laws will equally affect its conclusions with a change in that of the latter. The physical qualities of the soil, e. g. under the present constitution of nature are such, that, after a certain quantum of cultivation has been applied to a limited area, a further application is not attended with a proportionate return. The proof of this is, that, instead of confining cultivation to the best soils, and forcing them to yield the whole amount of food that may be required, it is found profitable to resort to soils of inferior quality.*

*

This doctrine has been denied, and some curious arguments have been advanced in refutation of it. The topic most insisted on by those who controvert it is the superior productiveness of agricultural industry in the United Kingdom at present, as compared with that which prevailed in former periods, notwithstanding the greater amount of capital now employed in agriculture. This argument would be good for something if all the other conditions of the problem were the same; but it is certain that they are not the same, and that they differ precisely in the point that is of importance-the superior skill with which capital and industry are at present applied. No economist, that I am aware of, has ever said that a small and unskilful application of capital to land would necessarily be attended with greater proportional returns than a larger outlay more skilfully applied; and it is to this assertion only that the argument in question applies.

But it is important to remark that the attempt to meet the doctrine in question by statistical data implies a total misconception, both of the fact which is asserted, and of the kind of proof which an economic doctrine requires. The doctrine contains, not an historic generalization to be tested by documentary evidence, but a statement as to an existing physical fact, which, if seriously questioned, can only be conclusively determined by actual experiment upon the existing soil. If

This physical fact, as every Political Economist knows, and as shall be explained on a future occasion, leads, through the play of human desires in the pursuit of wealth, to the phenomenon of rent, to the fall of profits as communities advance, and to a retardation

any one denies the fact, it is open to him to refute it by making the experiment. Let him show that he can obtain from a limited area of soil any required quantity of produce by simply increasing the outlay —that is to say, that, by quadrupling or decupling the outlay, he can obtain a quadruple or decuple return. If it be asked why those who maintain the affirmative of the doctrine do not establish their view by actual experiment, the answer is, that the experiment is performed for them by every practical farmer; and that the fact of the diminishing productiveness of the soil, is proved by their conduct in preferring to resort to inferior soils, rather than force unprofitably soils of better quality.

Mr. Carey, the American economist, has endeavoured to meet this reasoning by urging, that the conduct of farmers in resorting to inferior soils after the better qualities have been all taken into cultivation no more constitutes a proof that industry on the superior soils has become less productive, than the conduct of a cotton spinner in building a second factory, when his first is full, is a proof that manufacturing industry tends to become less productive, as manufacturing capital and labour increase. This is, in other words, to say, that the reason farmers do not increase their outlay on the soils of superior quality is, not because it would be unprofitable to do so, but for the same reason which limits the amount of capital and the number of hands employed in a cotton mill, namely, that, the necessary conditions of space being taken into account, it would be impossible to do So. No one who holds the received theory of rent will hesitate to stake the doctrine upon this issue. When any sane farmer in the United Kingdom, or in any other quarter of the civilized world, will give the same answer to the question-" why he does not manure more highly, or drain more deeply, or plough more frequently, a given field", which Mr. Carey gives-viz. "want of room", the disciples of Ricardo will be prepared to abandon their master; but, till this specimen of bucolic exegesis is produced, they will probably retain their present views.