These days, we call this idea Faraday’s Law of Induction: It says that a changing magnetic field will induce an emf in a loop of wire.

如今，我们将这个想法称为法拉第感应定律：它说变化的磁场会在线圈中感应出电动势。

Maxwell's first and second equations were so similar – one for electric fields and one for magnetic fields – that he knew there must be an equation that complemented Faraday's Law as well.

麦克斯韦的第一个和第二个方程非常相似——一个用于电场，一个用于磁场——他知道必须有一个方程来补充法拉第定律。