Friday, July 27, 2018


An Abney's Level
An 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. 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.
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.
Characteristics
1.    It can be use to determine the height of an object.
2.    It can be use as a leveling instrument also.
3.    It has also usage to measure the slope of a ground surface.
4.    Very small instrument so can be transport easily.
5.    Easy to use.
Main Parts
The abbey’s level consisting of three main parts as follows:
 
a.     Bubble Tube: A small bubble tube attached to a vernier arm is provided and it can be rotated with the help of a mild head screw or by rack and pin on arrangement. The image of the bubble is seen in the mirror. The arrangement is made such a way that whatever may be  position of telescope the tube is always horizontal.
b.    Graduated Arc: A semi circular graduated arc is provided to take the reading. The middle point of the arc is marked zero and it extends up to 90 degrees on either side. The zero mark coincide with zero mark of the vernier on the other side of the graduated arc gradient or slope are marked which can be read against outer or beveled edge of the vernier.
c.     Square Tube: The brass square tube is used for providing the line of site and it is provided with the hole or eye piece at one end and a cross wire with reflecting mirror at 45 degrees at the other end opening is provided just above the mirror to receive the rays from the bubble tube which is provided above it.
                      
How to Use an Abney

To determine the elevation difference between surveyor and a specific point:
Point the sight at the selected point for which you wish to know the elevation difference and view the location through the sight.  Holding the Abney steady read the angle difference from vertical off the side.  Next measure the ground distance from you to the selected point using paces or a measuring tape.  To calculate the vertical elevation, use the following equation:
Vertical Distance = Ground Distance x sin (angle)
After that, you have to add the calculated height with the height of eye level of surveyor. So, the total height of the object from ground surface will come.
Common uses
            Abney levels remain in common use in several fields:
·                     In topographic surveying, to place high precision surveying equipment, particularly in rough terrain.
·                     In forestry, for tree height measurement.
·                     In mining and mine safety inspection, to measure the grades of haulage roads.
·                     In geology, in measurements of rock outcrops and fault scarps.
References


A SHORT DESCRIPTION OF ABNEY’S LEVEL & HOW IT WORKS

An Abney's Level An  Abney level is an instrument used in  surveying  which consists of a fixed sighting tube, a movable spirit ...

 

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