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isomagnetic
isomagnetic adj. 
/ˌaɪsəmæɡˈnɛdɪk/ denoting a line (either imaginary or on a map) connecting places which have the same value of a particular parameter of the earth's magnetic field, and a map or chart showing such lines; also as n., an isomagnetic line.
Brit. /ˌʌɪsə(ʊ)maɡˈnɛtɪk/
, /ˌʌɪsə(ʊ)maɡˈnɛtɪk/U.S. /ˌaɪsoʊmæɡˈnɛdɪk/
, /ˌaɪsoʊmæɡˈnɛdɪk//ˌaɪsəmæɡˈnɛdɪk/ΘΚΠ
the world > the earth > earth sciences > geography > map-making > map > [noun] > line on map > magnetism
isomagnetic1898
isopor1931
the world > the earth > earth sciences > geography > map-making > map > [adjective] > line on map > magnetism
isomagnetic1898
isoporic1931
1898 J. Milne Seismol. xii. 225 Slight changes in the isomagnetics of a district.
1899 Nature 6 July 236/2 An opportunity will thus be afforded..to obtain some idea of the accuracy with which the isomagnetic lines can be determined.
1902 Encycl. Brit. XXX. 461/1 Formulæ giving smooth curves of continuous curvature, approximating as closely as possible to the district lines. These smooth curves are called terrestrial isomagnetics.
1940 S. Chapman & J. Bartels Geomagnetism I. iii. 96 The lines are called isomagnetic lines, and a chart in which the distribution of a magnetic element is thus indicated..is called an isomagnetic chart.
1967 E. H. Vestine in S. Matsushita & W. H. Campbell Physics of Geomagnetic Phenomena I. ii. ii. 185 The isomagnetic lines for declination D or variation of the compass are also called ‘isogonic’ lines.
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