A Topographic Abney Level 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. The Topographic Abney Level is an easy to use, relatively inexpensive, and when used correctly an accurate surveying tool. The Topographic Abney Level is used to measure degrees, percent of grade, topographic elevation, and chainage correction. By using trigonometry the user of a Topographic Abney Level can determine height, volume, and grade. The Topographic Abney Level is used at the eye height of the surveyor and is best employed when teamed with a second surveyor of the same eye height. This allows for easy sighting of the level and greater accuracy. A ranging pole can be marked at the eye height of the level user or the approximate location of the eye height (i.e. chin, nose, top of head) of the level surveyor must be know of the ranging surveyor.
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 know for his pioneering of color photography and color vision. Sir Abney invented this instrument under the employment of the School of Military Engineering in Chatham, England in the 1870's. It is described by W. & L. E. Gurley as an English modification of the Locke hand level, noting that it gives angles of elevation and is also divided for slopes, as 1 to 2, 2 to 1, etc. Since the main tube of this instrument is square, it can be applied to any plane surface. The clinometer scale is graduated to degrees, and read by vernier to 5 minutes.
Usage
Use of an Abney level is discussed in volume 12 of the Forest Quarterly1 published by the New York State College of Forestry in 1914. Discussion on the use of the Abney level starts on page 370.
;)
.jpg)
.jpg)
