can be said of Quasi-rents.' The eternal verity of the Ricardian theory is enhanced by Professor Marshall's re-statement—like the 'original and indestructible powers' of a soil upon which a new and splendid edifice has been erected. Indeed upon this topic and others the Principles of Economics may be regarded as a second approximation to truths with respect to which a first approximation was sufficient for Ricardo. The work before us is a signal example of 'the abandonment of dogma, the development of analysis,' which the author, in a striking passage added to the chapter on the growth of economic science, attributes to contemporary, in contrast to the older, economists. 'The change may perhaps be regarded as a passing onward from that early stage in the development of scientific method in which the operations of Nature are represented as conventionally simplified for the purpose of enabling them to be described in short and easy sentences to that higher stage in which they are studied more carefully and represented more nearly as they are, even at the expense of some loss of simplicity and definiteness.' We may couple this reflection with the new remarks in the following chapter on the difference between Comte and Mill as to the utility of an independent science of economics. 'What is wanted is a general principle which shall determine the point in the widening of the scope of economics at which the growing loss of scientific precision would begin to outweigh the gain of increasing reality and philosophic completeness.' We submit that our author has hit this point of maximum advantage better than if he had loaded his already weighty pages with all the details of law and industry, the absence of which an eminent German critic, otherwise favourable, has regretted.
The 'fundamental symmetry' between the action of supply and demand, to which we have referred as a conspicuous feature of the Principles of Economics, is brought out by the author with additional clearness through some alterations in the last book, of which we are told in the preface that 'they aim at emphasizing and defining more fully the distinguishing characteristics of the broad problem of Distribution, as contrasted with questions relating to the values of particular things; and at showing more clearly how, though the causes that govern demand and those that govern supply can be studied separately in the case of any single commodity, yet this cannot be done for the Agents of production as a whole.' Rehandling the complexities of Distribution, the author practises, while he explains, the 'law of Substitution;' combining the apparatus of symbols with the more familiar media of exposition in such proportions as may give the best result. What he says of material production is true also of the art of exposition. 'No two persons pursuing the same aims will adopt exactly the same routes.' There are those who would prefer to employ more copiously the terminology of the calculus, the conception of a function and its variations, in stating the theorem that 'the limit or margin at which the use of any one of these agents of production terminates, and the aid of another is substituted for it in any branch of production is
