Soft question. For surfaces in $\Bbb R^3$ (for example), there are two relevant curvatures: the Gaussian curvature $K$, and the mean curvature $H$. Thinking here, I realized that while calling the Gaussian curvature $K$ makes sense (since in German curvature is Krümmung), I have no idea why is the mean curvature denoted by $H$.
Is there any historical reason, or some word in German (or any other language) I'm missing?