The discovery and production of commodities require a knowledge of the distribution of geological formations for mineral products, of the natural distribution, life-conditions and cultivation or breeding of plants and animals and of the labour market. Attention must also be paid to the artificial restrictions of political geography, to the legislative restrictions bearing on labour and trade as imposed in different countries, and, above all, to the incessant fluctuations of the economic conditions of supply and demand and the combinations of capitalists or workers which affect the market.[54] The term "applied geography" has been employed to designate commercial geography, the fact being that every aspect of scientific geography may be applied to practical purposes, including the purposes of trade. But apart from the applied science, there is an aspect of pure geography which concerns the theory of the relation of economics to the surface of the earth. Conclusion. It will be seen that as each successive aspect of geographical science is considered in its natural sequence the conditions become more numerous, complex, variable and practically important. From the underlying abstract mathematical considerations all through the superimposed physical, biological, anthropological, political and commercial development of the subject runs the determining control exercised by crust-forms acting directly or indirectly on mobile distributions; and this is the essential principle of geography. (H. R. M.) FOOTNOTES: [1] A concise sketch of the whole history of geographical method or theory as distinguished from the history of geographical discovery (see later section of this article) is only to be found in the introduction to H. Wagner's _Lehrbuch der Geographie_, vol. i. (Leipzig, 1900), which is in every way the most complete treatise on the principles of geography. [2] _History of Ancient Geography_ (Cambridge, 1897), p. 70. [3] See J.L. Myres, "An Attempt to reconstruct the Maps used by Herodotus," _Geographical Journal_, viii. (1896), p. 605. [4] _Geschichte der wissenschaftlichen Erdkunde der Griechen_ (Leipzig, 1891), Abt. 3, p. 60. [5] Bunbury's _History of Ancient Geography_ (2 vols., London, 1879), Muller's _Geographi Graeci minores_ (2 vols., Paris, 1855, 1861) and Berger's _Geschichte der wissenschaftlichen Erdkunde der Griechen_ (4 vols., Leipzig, 1887-1893) are standard authorities on the Greek geographers. [6] The period of the early middle ages is dealt with in Beazley's _Dawn of Modern Geography_ (London; part i., 1897; part ii., 1901; part iii., 1906); see also Winstedt, _Cosmos Indicopleustes_ (1910). [7] From translator's preface to the English version by Mr Dugdale (1733), entitled _A Complete System of General Geography_, revised by Dr Peter Shaw (London, 1756).