Aquaculture Engineering

Compass surveying - Theory of magnetic compass

Unit 1- Surveying

Compass surveying

Theory of magnetic compass
Magnetic compass gives directly the magnetic bearing of line. The bearing may either be measured in the W.C.B system or R.B system.

The general principles of all magnetic compass depends upon the fact that, if a long, narrow strip of steel or iron is magnetized and is suitably suspended or pivoted about a point near its centre. So that it can oscillate freely about the vertical axis, it will tend to establish if self in the magnetic meridian at the place of observation.

The most essential features of a magnetic compass are

• Magnetic needle - to establish the magnetic meridian
• A line of sight -To sight the other end of the line
• A graduated circle - Either attached to the box or to needle to read the direction of the lines
• A compass box - To house above parts
• A tripod - used to support the box

Following are the different types of compass

• Surveyor’s compass
• Prismatic compass
• Transit or level compass