French labourers. Such differences in the value of labour mainly depend upon superior strength and stamina, but still greater differences arise from superior skill; many operations in the manufacture of commodities require, perhaps, a delicate touch or a quick dexterity which no amount of untrained labour could supply. and capital.Capital, directed by superior knowledge, may effect what before was impossible; mines are now worked which no amount of labour or capital, unaided by the steam-engine, could have drained; and the application of a hundred times as much labour and capital would not produce the cloth which is now woven by the spinning-jenny and the power-loom. These considerations may, perhaps, suggest the opinion that we shall be obliged to call in the assistance of every science in order to investigate the laws which determine the productiveness of land, labour, and capital. For it may be said, agricultural chemistry makes known the constituents upon which depend the fertility of the soil; the difference in the stamina and strength of English and Russian labourers must be elucidated by appealing to physiology, and to other sciences. Again, the efficiency of machinery must be explained by the principles of mechanics. It, therefore, manifestly becomes necessary to place some limitation upon the scope of political economy, unless it is intended to embrace a vast number of other sciences. Now, it will be remembered, that no accurate definition of political economy was attempted to be given at the commencement of this work. It is far better that the reader should have the definition evolved for him as the subject gradually progresses.
A necessary limitation of our inquiries into the cause of this variation.In the introductory chapter we described political economy to be the science which investigates the laws that determine the production, the distribution, and the exchange of wealth; it was, however, at the same time stated that this was rather a general description than an accurate definition. It is not an accurate definition, for it is already perceived that, even concerning the first branch of the subject, political economy does not investigate all the laws which concern the production of wealth; for if it did investigate those laws, chemistry, physiology, mathematics, and various other branches of