with little variation, of the other occupations which it represents; of all the arts which extract materials from the globe. Mining industry, for example, usually yields an increase of produce at a more than proportional increase of expense. It does worse, for even its customary annual produce requires to be extracted by a greater and greater expenditure of labour and capital. As a mine does not reproduce the coal or ore taken from it, not only are all mines at last exhausted, but even when they as yet show no signs of exhaustion, they must be worked at a continually increasing cost; shafts must be sunk deeper, galleries driven farther, greater power applied to keep them clear of water; the produce must be lifted from a greater depth, or conveyed a greater distance. The law of diminishing return applies therefore to mining, in a still more unqualified sense than to agriculture: but the antagonizing agency, that of improvements in production, also applies in a still greater degree. Mining operations are more susceptible of mechanical improvements than agricultural: the first great application of the steam-engine was to mining; and there are unlimited possibilities of improvement in the chemical processes by which the metals are extracted. There is another contingency, of no unfrequent occurrence, which avails to counterbalance the progress of all existing mines towards exhaustion: this is, the discovery of new ones, equal or superior in richness.
To resume; all natural agents which are limited in quantity, are not only limited in their ultimate productive power, but, long before that power is stretched to the utmost, they yield to any additional demands on progressively harder terms. This law may however be suspended, or temporarily controlled, by whatever adds to the general power of mankind over nature; and especially by any extension of their knowledge, and their consequent command, of the properties and powers of natural agents.
