A dip needle arranged to move freely in the magnetic meridian dips by an angle `theta`. The vertical plane in which the needle moves is now rotated through an angle `alpha` from the magnetic meridian. Through what angle the needle will dip in the new position?

Explanation

If the apparaent dip is `delta` the true , dip is `delta` and the angle of rotation of plane is `alpha` then
` cot delta = cot delta cos alpha`.
`therefore cot delta lt cot delta `
Thus the angle is less then `delta`.