tailieunhanh - An Encyclopedia of the History of Technology part 42

An Encyclopedia of the History of Technology part 42. This one of a kind encyclopedia presents the entire field of technology from rudimentary agricultural tools to communication satellites in this first of its kind reference source. Following an introduction that discusses basic tools, devices, and mechanisms, the chapters are grouped into five parts that provide detailed information on materials, power and engineering, transportation, communication and calculation, and technology and society, revealing how different technologies have together evolved to produce enormous changes in the course of history | PART TWO POWER AND ENGINEERING in the direction of increasing the accuracy of measurement and in this the screw is of major importance. The ability to manufacture accurate screw threads has been critical in the design of instruments for astronomy navigation time measurement the production of screw controlled machine tools and engineering inspection devices. The measurement of time based on observation of the sun s passage has always exercised the mind of man and many methods have been explored. By the ninth century AD the Chinese had combined hydraulic and mechanical methods to make a large water clock which showed the time by ringing bells and the appearance of various figures. The first all-mechanical clocks were made in Europe the most outstanding example being that produced by Giovanni de Dondi c. 1364 which incorporated elliptical gear wheels and sun and planet gears all cut by hand. A replica has been exhibited in the Science Museum London. The oldest clock in England is that at Salisbury Cathedral constructed c. 1386 in a similar way with forged iron gears and lantern pinions all held in an iron framework joined by rivets and wedges. These construction methods while adequate for large public clockwork were not suitable for the smaller timekeepers which the people sought and the size of this demand and the development of the designs led to improvements in machining including accurately cut gears turned spindles and screws which were in advance of general manufacturing by 300 years. During this period the spring-driven pocket watch made its appearance and with it the need for a device to control the pull of the spring to exert a constant force throughout its unwinding. The fusee invented c. 1450 consists of a conical drum with a spiral groove carrying a chain or cord which attached to the end of the spring controls its force by unwinding from a different part of the drum as the spring runs down. Manufacturing fusees called for an extension to the machining .