Theory
An abney level is one of the popular form of clinometer. The instrument which are used for rough work to measure verticle angles or observe the slope of the ground or to locate the points on a given grade are known as clinometer.
The instrument is light compact handy and very convenient for speedy rough work. It measure angle of elevation or depression with an accuracy of 10 min.
Diagram
Construction
Essential parts of abney level are maintained below
a) Bubble tube
A small bubble tube attached to a vernier arm is provided and it can be rotated with the helps 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 extend upto 600 or 900 on either side. The zero mark coincide with zero mark of the vernier on the other side of the graduated arc gradiant 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 450 at the other end opening is provided just above the mirror to receive the rays from the bubble tube which is provided above it.
