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isoporic
isoporic adj.
Brit. 
/ˌʌɪsə(ʊ)ˈpɒrɪk/
, /ˌʌɪsə(ʊ)ˈpɒrɪk/U.S. /ˌaɪsəˈpɔrɪk/
/ˌaɪsəˈpɔrɪk/ΘΚΠ
the world > the earth > earth sciences > geography > map-making > map > [adjective] > line on map > magnetism
isomagnetic1898
isoporic1931
1931 Compt. Rend. de l'Assemb. de Stockholm 1930 (Union Géod. et Géophys. Internat., Sect. de Magn. et Électr. Terr.) 280 A consideration of the most recent published results of secular-variation observations..has revealed some very interesting and important conditions governing isoporic movements.
1940 S. Chapman & J. Bartels Geomagnetism I. iii. 114 The rate of the secular variation in each element at any epoch..can..be represented by..isoporic charts, a term proposed by Harradon.
1973 M. W. McElhinny Palaeomagnetism & Plate Tectonics i. 6 Isoporic foci are not permanent, but grow and decay, their lifetime being of the order of 100 years, during which they move on the earth's surface in a somewhat irregular fashion.
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