Which WWI innovation was used to measure changes in the vertical components of the earth's magnetic field?

• A. Seismograph
• B. Gyroscope
• C. Magnetometer
• D. Gravimeter

Answer: (C)

The main idea here is sensing magnetic fields, not movements, gravity, or rotation. A magnetometer is designed to detect magnetic field strength and direction, including the vertical component of Earth’s field, so it can track how that vertical component changes over time. Seismographs record ground vibrations, not magnetic fields; gyroscopes measure rotation or orientation; gravimeters measure gravity. Because the question asks for measuring changes specifically in the vertical component of Earth’s magnetic field, the magnetometer is the instrument that directly provides that information.