He who has improved upon previous conceptions, and been the only one to make any very important advance in the science since Mill’s day, is J. E. Cairnes,(47) in his “Leading Principles of Political Economy newly expounded” (1874). Scarcely any previous writer has equaled him in logical clearness, originality, insight into economic phenomena, and lucidity of style. He subjected value, supply and demand, cost of production, and international trade, to a rigid investigation, which has given us actual additions to our knowledge of the study. The wages-fund theory was re-examined, and was stated in a new form, although Mr. Mill had given it up. Cairnes undoubtedly has given it its best statement. His argument on free trade (Part III, chapter iv) is the ablest and strongest to be found in modern writers. This volume is, however, not a systematic treatise on all the principles of political economy; but no student can properly pass by these great additions for the right understanding of the science. His “Logical Method of Political Economy” (1875) is a clear and able statement of the process to be adopted in an economic investigation, and is a book of exceptional merit and usefulness, especially in view of the rising differences in the minds of economists as to method. A group of English writers of ability in this period have written in such a way as to win for them mention in connection with Cairnes and Mill. Professor W. Stanley Jevons(48) put himself in opposition to the methods of the men just mentioned, and applied the mathematical process to political economy, but without reaching new results. His most serviceable work has been in the study of money, which appears in an excellent form, “The Money and Mechanism of Exchange” (1875), and in an investigation which showed a fall of the value of gold since the discoveries of 1849. In this latter he has furnished a model for any subsequent investigator. Like Professor Jevons, T. E. Cliffe Leslie(49) opposed the older English school (the so-called “orthodox”), but in the different way of urging with great ability the use of the historical method, of which more will be said in speaking of later German writers.(50) He also distinguished himself by a study of land tenures, in his “Land Systems and Industrial Economy of Ireland, England, and Continental Countries” (1870), which was a brilliant exposition of the advantages of small holdings.