Đang chuẩn bị liên kết để tải về tài liệu:
An Encyclopedia of the History of Technology part 64

An Encyclopedia of the History of Technology part 64. 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 THREE TRANSPORT Throughout the nineteenth century ballooning was largely an activity for showmen with a limited number of ascents for scientific mainly meteorological purposes. Most of these flights were made using coal-gas which was conveniently available in most towns from about 1820. Charles Green was the first to use coal-gas in London in 1821 although the Academy of Lyons had suggested it in 1784. Coal gas is heaver than hydrogen so a somewhat larger balloon was needed but the lower cost and the convenience of inflating from a permanent supply were great advantages. Hot-air balloons were used occasionally during the nineteenth and early twentieth centuries but their very large size compared to gas balloons made them difficult to handle and it was only when sheer size was a desirable feature required by an entrepreneur that they were noticed. However it was often realized that if a continuous supply of heat could be contrived hot-air balloons could be useful in remote places where coal gas or hydrogen was not conveniently available. Experiments on these lines were regularly made using alcohol or petroleum fuels from the latter part of the nineteenth century onwards. Another interesting but abortive proposal was to combine the constant lift of a hydrogen balloon with the variable lift of a hot-air balloon carrying a fuel supply. This concept was first tried by Pilatre de Rozier the pilot of the first Montgolfier balloon in 1785. He made a combination balloon which had a conventional hydrogen balloon on top of a cylindrical bag heated by a brazier fuelled with straw blocks. Its only flight on 15June 1785 was an attempt to cross the English Channel from Boulogne this ended in disaster when the balloon caught fire after a few minutes flight. Subsequent attempts to produce combination balloons were equally unsuccessful though not so spectacularly fatal. Although the use of balloons for military observation purposes was pioneered by the French in 1794 it was .