He's trying to relax us here by slowing down the rate of harmonic change here.

他希望通过减慢泛音的变化速度让大家在这里快要睡着了。

耶鲁公开课 - 聆听音乐课程节选

du/dV under constant temperature was equal to zero for an ideal gas. And by analogy, we expect the same thing to be true here, because enthalpy and energy have all this analogy going on here. So let's look at an ideal gas.

偏U偏V在恒温下等于零,可以类比，我们希望在这里也一样，因为焓和能量有很强的类比性，让我们看看理想气体,【理想气体】

麻省理工公开课 - 热力学与动力学课程节选