"Growing skill in the working of metals is... exemplified by the development of the instrument-maker's craft. To many... we make reference elsewhere—for example, clocks, navigational instruments and balances. ...Brass, ivory, and closed-grained woods, such as box and pear, were the principal materials of the instrument-makers, with brass becoming increasingly favoured because of its rigidity and permanence. For the shaping of metal the lathe was a valuable tool, and the clock-makers in particular developed it greatly for precision work. The engraving of scales was, of course, a most important part of the work: until the advent of mechanical devices, this was done with simple engraving tools and punches, the design being first set out by geometrical methods. The earliest products of the instrument-makers were made mainly for astronomical purposes or to apply astronomical methods in navigation: they included astrolabes, cross-staffs, quadrants, sundials, and orreries, as well as basic geometrical instruments such as compasses and rules. From the seventeenth century, however, a variety of new instruments, or much improved versions of old ones, began to appear. The needs of surveyors led to the elaboration of the hodometer... enabling distances to be measured... Improvements in artillary called for more accurate sighting of cannon, and by the beginning of the seventeenth century the gunner's level had been highly developed. The invention of the telescope and microscope introduced new problems both in the making of lenses and of the instruments in which they were mounted: the new instruments were a regular part of the instrument-maker's trade from about 1660. From 1700 the revolution in science was making still further demands on the craft, and air-pumps, thermometers, barometers, electrical machines, and other instruments were called for in constantly increasing quantities."