Lothar Meyer's curve was a plot of atomic volume against atomic mass.
Meyer’s main contribution to atomic theory was his recognition of the periodic behaviour of atomic properties.
He plotted the atomic volume (the volume of a mole of atoms) of an element against its atomic mass. Here's his curve.
It showed a periodic pattern as the atomic volume rose to peaks and then fell again.
For example, the alkali metals occupied the peaks of the curve, which dropped to a minimum before rising to the next peak.