In magnetism and surveying, the vertical angle made by the longitudinal axis of a freely suspended magnetic needle with the horizontal at its pivot is called what? Select the correct geomagnetic term.

Introduction / Context:
Geomagnetic terminology is foundational for surveying and navigation. A magnetic needle aligns with the local magnetic field, which is generally not horizontal. The vertical angle from the horizontal is a key parameter measured with a dip circle or equivalent instrument.

Given Data / Assumptions:

• The needle is free to swing in a vertical plane aligned with magnetic meridian.
• We are distinguishing among several related angular terms.
• Standard surveying definitions apply.

Concept / Approach:

“Dip” (magnetic inclination) is the vertical angle between the needle and the horizontal. “Declination” is the horizontal angle between true north and magnetic north. “Azimuth” is a horizontal direction angle from a reference meridian. “Bearing” is the acute horizontal angle from a reference line in a quadrant system. “Deviation” often refers to compass error due to local attraction. Thus, the only vertical-plane term in the list is dip.

Step-by-Step Solution:

Verification / Alternative check:

Survey texts define dip as the angle of the earth’s magnetic field with respect to the horizontal; instruments like the dip circle are used to measure it.

Why Other Options Are Wrong:

Declination/azimuth/bearing are horizontal angles; deviation is not the standard name for the vertical angle.

Common Pitfalls:

Confusing declination (horizontal) with dip (vertical); mixing “inclination” and “dip”—they are synonyms here.

Final Answer:

Dip