It is said that Frontinus, a Roman Consul, and inspector of public fountains and aqueducts in the reigns of Nerva and Trajan, and who wrote a book, _De Aquaeductibus Urbis Romae Commentarius_, describing the great aqueducts of Rome, was the first and the last of the ancients to attempt a scientific investigation of the motions of liquids. In 1593 Serviere, a Frenchman, born in Lyons, invented the rotary pump. In this the pistons consisted of two cog wheels, their leaves intermeshing, and rotated in an elliptical shaped chamber. The water entered the chamber from a lower pipe, and the action of the wheels was such as to carry the water around the chamber and force it out through an opposite upper pipe. Subsequent changes involved the rotating of the cylinder instead of the wheels and many modifications in the form of the wheels. The same principle was subsequently adopted in rotary steam engines. In 1586, a few years before this invention of Serviere, Stevinus, the great engineer of the dikes of Holland, wrote learnedly on the _Principles of Statics and Hydrostatics_, and Whewell states that his treatment of the subject embraces most of the elementary science of hydraulics and hydrostatics of the present day. This was followed by the investigations and treatises of Galileo, his pupil Torricelli, who discovered the law of air pressure, the great French genius, Pascal, and Sir Isaac Newton, in the 17th century; and Daniel Bernoulli, d’Alembert, Euler, the great German mathematician and inventor of the centrifugal pump, the Abbé Bossut, Venturi, Eylewein, and others in the 18th century. It was not until the 17th and 18th centuries that mankind departed much from the practice of supplying their towns and cities with water from distant springs, rivers and lakes, by pipes and aqueducts, and resorted to water distribution systems from towers and elevated reservoirs. Certain cities in Germany and France were the first to do this, followed in the 18th century by England. This seems strange, as to England, as in 1582 one Peter Maurice, a Dutch engineer, erected at London, on the old arched bridge across the Thames, a series of forcing pumps worked by undershot wheels placed in the current of the river, by which he forced a supply of water to the uppermost rooms of lofty buildings adjacent to the bridge. Before the inventions of Newcomen and Watt in the latter part of the 18th century of steam pumps, the lift and force pumps were operated by wheels in currents, by horses, and sometimes by the force of currents of common sewers. When the waters of rivers adjacent to towns and cities thus began to be pumped for drinking purposes, _strainers_ and _filters_ of various kinds were invented of necessity. The first ones of which there is any printed record made their appearance in 1776.