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A continuous and adequate sample with which to test Wegener's hypothesis can be found in the mineral record of changes in the earth's magnetic orientation. Additional geological and geophysical evidence has come from studies of the topography magnetism and magnetism of the ocean floor, geographic fit of the continents, and geochronology (sequence and age of rocks on separated continents). (See BREAKTHROUGH in Year in Review: GEOLOGY, GEOCHEMISTRY, AND GEOPHYSICS.)

He was a trustee of the University of Pennsylvania in 1871-86, presented to the university a valuable library of works on engineering in 1878, and finally resigned his trusteeship because of continued residence abroad. Besides various valuable scientific papers he wrote 'Terrestrial Magnetism and the Magnetism of Iron Ships' (1883) ; and 'Manual of Coaching' (1900)).

There are several mechanical arrangements o armature and field magnets, but all produce elec tricity, some more efficiently than others. Thi amount of electricity produced by a generator de pends upon the number of magnetic lines of fora (magnetism) and the rapidity or speed with whicl they are cut (or passed through) by the arma ture conductors. The product of these two items magnetism and speed, determines the size of : generator.