His speech was so brilliant that the audience was drawn to him magnetically.

magnetically 是形容词 magnetic（有磁性的）的副词形式，由名词 magnet（磁铁）加形容词后缀 -ic 构成形容词，再加副词后缀 -ally 构成副词。 magnetic 本义指"有磁性的"，引申为"有吸引力的"。 magnetically 在这里比喻观众像被磁铁吸引一样不由自主地被演讲者吸引。