the many different machines used for engineering structures such as hoists, cranes and pulleys, as well as war machines such as catapults, ballistae, and siege engines. As a practising engineer, Vitruvius must be speaking from personal experience rather than simply describing the works of others. He also describes the construction of sundials and water clocks, and the use of an aeolipile (the first steam engine) as an experiment to demonstrate the nature of atmospheric air movements (wind). Aqueducts His description of aqueduct construction includes the way they are surveyed, and the careful choice of materials needed, although Frontinus (a general who was appointed in the late 1st century AD to administer the many aqueducts of Rome), writing a century later, gives much more detail of the practical problems involved in their construction and maintenance. Surely Vitruvius' book would have been of great assistance in this. Vitruvius was writing in the 1st century BC when many of the finest Roman aqueducts were built, and survive to this day, such as those at Segovia and the Pont du Gard. The use of the inverted siphon is described in detail, together with the problems of high pressures developed in the pipe at the base of the siphon, a practical problem with which he seems to be acquainted. Materials He describes many different construction materials used for a wide variety of different structures, as well as such details as stucco painting. Concrete and lime receive in-depth descriptions. Vitruvius is cited as one of the earliest sources to connect lead mining and manufacture, its use in drinking water pipes, and its adverse effects on health. For this reason, he recommended the use of clay pipes and masonry channels in the provision of piped drinking-water. Vitruvius is the source for the anecdote that credits Archimedes with the discovery of the mass-to-volume ratio while relaxing in his bath. Having been asked to investigate the suspected adulteration of the gold used to make a crown, Archimedes realised that the crown's volume could be measured exactly by its displacement of water, and ran into the street with the cry of Eureka! Dewatering machines He describes the construction of Archimedes' screw in Chapter X (without mentioning Archimedes by name). It was a device widely used for raising water to irrigate fields and drain mines. Other lifting machines he mentions include the endless chain of buckets and the reverse overshot water-wheel.