Same as Neutral Center, etc.
"Taking into consideration even the introductory conditions of the etheric stage, etheric vibration has proved to me that the higher the velocity of its rotating stream the greater is its tendency towards the neutral centre or centre of sympathetic coincidence. Were it otherwise, how could there ever be any planetary formations of the building up of visible structure? If a billiard ball were rotated to a certain velocity, it would separate in pieces, and the pieces would fly off in a tangent; but if it were a ball of ether, the higher the velocity of rotation the stronger would be the tendency of its corpuscles to seek its centre of neutrality, and to hold together." [Vibratory Physics - The Connecting Link between Mind and Matter]
"The activity of the corpuscles represents its outflow from the luminiferous track towards the molecular centers of neutrality, revealing the connecting link between mind and matter." [Keely, Dashed Against the Rock]