Q)The plane of a dip circle is set in geographic meridian and the apparent dip is δ1. It is then set in a vertical plane perpendicular to the geographic meridian. The apparent dip angle is δ2. The declination θ at the plane is- Ans) θ=tan-1(tanδ1/tanδ2)
Attempt: tanδ=Bv/Bh where δ is angle of dip, Bv and Bh are vertical and horizontal components of Earth’s Magnetic Field at the location of dip circle. For the two cases, Bh would differ. My book says Bh1 would be Bhcosθ and Bh2 would be Bhcos(90-θ). Taking these in the equation, i can get the above mentioned answer. What I am having trouble understanding is how these values of Bh came to be? Could someone guide me with the help of a figure or something? Thank you.