Magnetism. The Chinese were the first to study theories of magnetism: polarity (the condition of opposite properties); induction (the process by which an object becomes magnetized); retentivity (the capacity for retaining magnetism); and variation (the measurement of change in magnetism). These theories were identified much earlier in China than in Europe, although Europeans performed the first experiments relating to electric charges and magnetism in the seventeenth century. Chinese notions about magnetic phenomena were connected with cosmic theories that probably made their influence felt in Europe by the eighteenth century. The magnetic North Pole is about 1,200 miles from the geographical true north of the earth. The difference between the true geographical North Pole and the magnetic North Pole was identified as the angle of declination. (It is not constant and frequently shifts.) By the ninth century the Chinese had discovered this magnetic declination...