n.极性；磁性引力；两极
Polarity is inherent in a magnet. 极性是磁铁的固有性质。
Note the polarity of the voltage drop across R. 注意R上电压降的极性。
The hydrophobicity is related to molecular volume and polarity. 分子的疏水性跟分子的体积和极性有关。
The field is strongest at the poles, diminishes at the equator, and differs in polarity from the Northern to the Southern Hemisphere. 南北两极的磁场最强，赤道上磁场较为微弱，而各地的磁性也会因纬度而改变。
