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 toward 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.
Chapter X. Consequences Of The Foregoing Laws.
§ 1. Remedies for Weakness of the Principle of Accumulation.
From the preceding exposition it appears that the limit to the increase of production is twofold: from deficiency of capital, or of