The English system consists more in the use of extended and successive reservoirs or beds of sand alone, or aided by the use of the sulphate. This also is extensively used in many large cities. CHAPTER XII. PNEUMATICS AND PNEUMATIC MACHINES. “The march of the human mind is slow,” exclaimed Burke in his great speech on “Conciliation with the Colonies.” It was at the beginning of the last quarter of the 18th century that he was speaking, and he was referring to the slow discovery of the eternal laws of Providence as applied in the field of political administration to distant colonies. The same could then have been said of the march of the human mind in the realms of Nature. How slow had been the apprehension of the forces of that kind but silent Mother whose strong arms are ever ready to lift and carry the burdens of men whenever her aid is diligently sought! The voice of Burke was, however, hardly silent when the human mind suddenly awoke, and its march in the realms of government and of natural science since then cannot be regarded as slow. More than fifteen centuries before Burke spoke, not only had Greece discovered the principles of political freedom for its citizens and its colonies, but the power of steam had been discovered, and experimental work been done with it. Yet when the famous orator made his speech the Grecian experiment was a toy of Kings, and the steam engine had just developed from this toy into a mighty engine in the hands of Watt. The age of mechanical inventions had just commenced with the production of machines for spinning and weaving. And yet, in view of the rise of learning, and the appearance from time to time of mighty intellects in the highest walks of science, the growth of the mind in the line of useful machinery had indeed been strangely slow. “Learning” had revived in Italy in the 12th and 13th centuries and spread westward in the 14th. In the 15th, gunpowder and printing had been discovered, and Scaliger, the famous scholar of Italy, and Erasmus, the celebrated Dutch philosopher, were the leading restorers of ancient literature. Science then also revived, and Copernicus, the Pole, gave us the true theory of the solar system. The 16th century produced the great mathematicians and astronomers Tycho Brahe, the Dane, Cardan and Galileo, the illustrious Italians, and Kepler, the German astronomer, whose discovery of the laws of planetary motion supplemented the works of Copernicus and Galileo and illuminated the early years of the 17th century.