a. [mod. f. Gr. ἄγων-ος, ἀγώνι-ος, without angle (f. ἀ priv. + γωνία angle), + -IC.] Having or making no angle, having no inclination; as in agonic line, the irregular line passing through the two magnetic poles of the earth along which the magnetic needle points directly north or south; the line of no magnetic variation.
1863. Atkinson, trans. Ganot’s Physics, VIII. § 674. In certain parts of the earth the magnet coincides with the geographical meridian. These points are connected by an irregularly curved imaginary line, called a line of no variation or agonic line.
