I'm sure that's super elevation.
In my research for mine locos and general mine railroad information I came across several late 1800's technical books that extensively described track methods, engineering formulas for rail weight selection, tie size and placement, turnout styles with selection guidelines, etc, etc. Very much included was the whys and wherefores of super elevation, even in underground mine track. We know that wasn't always followed but the detailed knowledge, engineering, and reasoning was very clearly understood and recommended practice.
I enjoy old engineering books and am surprised (used to be) at the very legitimate engineering knowledge that existed even in the 1800's. In many areas of engineering very little is really new. New components or new materials and methods, sure, but they are details that make it easier to produce or make available options that didn't exist for the absence of those capable materials or methods. Still, the bulk of the engineered devices still in use, even breakthroughs, are built on old engineering news.
