Magnetic Dip

An entirely balanced, freely suspended magnetic needle dips towards its northern end in northern hemisphere and towards its southern end in southern hemisphere. If it is at North Pole, the needle takes vertical position. At that place between the horizontal and the direction shown by a perfectly balanced and freely suspended needle the vertical angle is known as the magnetic dip. Its value is 0° at equator and 90° at magnetic poles. A sliding rider (weight) is provided on the needle to counteract the dip.

Example: True bearing of line AB is 357° and its magnetic bearing is 1° 30′. Find out the declination. Also find the true bearing of AC which has magnetic bearing equal to 153° 30′.

Solution

Magnetic Declination = 1° 30′ + (360° - 357°) = 4° 30′, west. Magnetic bearing of AC = 153° 30′.

1° 30

∴          True bearing of AC = 153° 30′ - 4° 30′ = 149°            Ans.