PHYSICAL RESOURCES. Though the term "physical" or "natural" resources has no precise definition, it may be taken to designate those things, inert substances, living organisms and effective combinations or products of natural forces, which men utilize to promote their material well-being.
An analytical classification of natural resources might rest on any one of several bases. The historical method might be fol lowed, since it is known that primitive men first made use of vegetable materials, later domesticated animals and finally arrived, at a relatively recent time, at a state of civilization in which the extensive use of minerals is the most important characteristic. As this coincides with fundamental distinctions as to the nature of the resources themselves, it will, in general, be followed here. Another basis of classification might be the human needs which they serve, but such a classification would be confusing, since both vegetable and animal products are used for such diverse purposes as food and clothing, while mineral products as well as the other two are used for shelter. Still another basis of classification might be a division into those resources which men use as a source of energy, and those which are used in connection with its applica tion or production. This classification is also partly followed.
Underlying these considerations is the more fundamental view of natural resources as the principal things that are utilized in the satisfaction of human wants. The most fundamental of these are air, water, food and sunlight. Shelter, clothing and a variety of simple tools are more complex wants and illustrate the kinetic aspect of human needs. The horses, cattle, dogs and other ani mals of to-day do not (broadly speaking) want anything beyond what the same animals wanted in 500o s.c., while the wants of men have greatly increased and diversified during the same period. Much of the material that is utilized to-day owes its useful ness to the way in which it satisfies mental and spiritual rather than purely physical needs. Raw materials therefore pass through repeated transformations and modifications before they serve their final end. A symphony concert, heard over the radio, is related in a remote and complex way to the lumps of ore and fragments of wood which are the basic components of the musical instruments. Though natural resources will be here discussed in their material aspects they are also involved, in a most impor tant and essential way, in the mental and spiritual life of men.
Most of the energy-imparting resources have their basal origin in the radiant energy from the sun. The animal products which men utilize, have been derived by metabolism from vegetable life, and this is in turn the product of the action of living cells upon inert substance, resulting from the energy input of the sunlight. E. E. Slosson has estimated that the heat received by radiation from the sun in a growing season in the latitude of Washington, D.C., amounts per acre to more than would be produced by burning over 200 tons of coal, while the heat value of the corn (maize) grown on an acre in a season amounts to less than that in half a ton of coal. The energy content of coal is ultimately derived
from sunlight, and evidence strongly indicates that petroleum and natural gas are decomposition products derived from organic material. Their energy content is derived from the same source.
Water is, similarly, another of the great natural resources, since it is an essential to the life of both plants and animals. The amount of it present in the atmosphere determines, to a large degree, the character of the vegetable and animal life in a given area, while in the descent over the land surface it may be utilized as a perpetual source of power.
The atmosphere is almost never thought of as a natural resource, because it is everywhere present and freely available to all. Yet its oxygen content is essential to all animal life and to the corn bustion by which power is derived from the hydrocarbons, while its rather small content of carbon dioxide forms, with water and sunlight, the basic components of vegetable life. It also furnishes the mechanism by which water is enabled to maintain its cycle of distribution. Its vital importance as a cooling agent to the human body, considered as a machine, and upon human health, has only become fully recognized within the present century.
Soil, as the rather complex superficial layer which covers the earth's surface is termed, is also an important basic natural re source. It furnishes not only the mineral constituents necessary for plant growth but also the physical conditions which are equally essential. The nature of the soil of a region affects, to a con siderable degree, the civilization which may there develop. The character of the soil, in turn, is profoundly affected by climate. Vegetation, forests and animal life are in turn affected by soil and climate, so that these natural resources are complexly inter related.
The inert natural resources, which may be thought of as static rather than kinetic, may be subdivided into those that are sources of energy, and those which are utilized in other ways. One sig nificant difference is that the first group are destroyed in use, while the others are permanent, to a varying degree. Most of the gold that has been produced is still available, while most of the coal that has been produced has been completely destroyed. The lead in storage batteries, on the other hand, is almost com pletely salvaged and re-used, while that used in paint is almost completely lost. The steadily growing use of natural resources such as these and the fact that the quantity of each now available by the present methods of production has, in every case, some limit and in many cases one that, at the present rate of increasing consumption, is near enough in the future to be a source of real concern, make it appropriate to include in an article on natural resources a discussion of possible substitutes.
The discussion given below is divided as follows: (r) energy group; (2) metallic and non-metallic group; (3) precious metals group; (4) rare metals group; (5) substitutes for natural resources. (T. T. R.)