Heart rocker

Alfred W. Bruce wrote in The Steam Locomotive in America:


 * The inverted-rocker device was introduced about 1914. The inverted rocker was a heart-shaped rocker resting on two rolling contacts at the bottom and supporting two inclined planes at the top--one on each side of its apex center point.  Thus movement in either direction produces a rolling-contact support which permits ample lateral movement with nearly any desired resistance characteristic, a quality that has retained this device in use today [approx. 1952].