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An Abney level and clinometer, is an instrument used in surveying which consists of a fixed sighting tube, a movable spirit level that is connected to a pointing arm, and a protractor scale. An internal mirror allows the user to see the bubble in the level while sighting a distant target. It can be used as a hand-held instrument or mounted on a Jacob's staff for more precise measurement, and it is small enough to carry in a coat pocket.〔Smaller Instruments and Appliances: The Abney Level and Clinometer, (A Manual of the Principal Instruments used in American Engineering and Surveying ), W. & L. E. Gurley, Troy, NY, 1891; page 219.〕〔George William Usill, Clinometers: The Abney Level, (Practical Surveying ), Crosby Lockwood and Son, London, 1889; page 33.〕 The Abney level is an easy to use, relatively inexpensive, and, when used correctly, an accurate surveying tool. Abney levels typically include scales graduated in measure degrees of arc, percent grade, and in topographic Abney levels, grade in feet per surveyor's chain, and chainage correction. The latter is the cosine of the angle, used to convert distances measured along the slope to horizontal distances. By using trigonometry the user of an Abney level can determine height, volume, and grade.〔H. A. Calkins and J. B. Yule, (The Abney Level Handbook ), United States Forest Service, 1927.〕 Abney levels are made with square tubular bodies so that they may also be used to directly measure the slopes of plane surfaces by simply placing the body of the level on the surface, adjusting the level, and then reading the angle off of the scale. == Origins == The Abney level was invented by Sir William de Wiveleslie Abney (Born 24 Jul 1843 Died 3 Dec 1920) who was an English astronomer and chemist best known for his pioneering of color photography and color vision. Abney invented this instrument under the employment of the School of Military Engineering in Chatham, England prior to late 1870. It is described by W. & L. E. Gurley as an English modification of the Locke hand level.〔 Elliott Brothers of London registered an "improved clinometer and spirit level combined" in December 1870 based on "the old form as originally designed by Lieutenant Abney."〔Combined Clinometer and Spirit Level, (The Mechanics Magazine ), Dec. 30, 1870; page 476.〕 By 1871, a committee of the Royal Geographical Society recommended a long list of instruments that explorers should carry. Along with necessary tools such as a watch, compass, sextant and plenty of paper, the committee included "a pocket level (Abney's)" in a secondary list of "additional instruments, not necessary, but convenient." 〔Admiral Sir George Back, Vice-Admiral Richard Collinson, and Francis Galton, Hints to Travellers (Third and Revised Edition), (Proceedings of the Royal Geographical Society ), Vol. XVI, No. 1 (Dec. 18, 1871).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Topographic Abney level」の詳細全文を読む スポンサード リンク
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