Definition of "unsteadying"

A correspondent suggested that the superior riding qualities of the latter were due to the absence of piston-valve chests above the cylinders, which made it possible to bring the underside of the water-tanks to a lower level than that of the "Rivers", so minimising the unsteadying effect of water surging in the tanks.

1944 May and June, “Notes and News: Tank Engine Stability”, in Railway Magazine, page 185