(under subclass 44.2) Apparatus wherein the motor comprises an electrical circuit and the sensing means includes a flexible structure which is capable of expanding to increase the volumetric capacity thereof, said structure comprising (a) a tube of flexible material having a circumferentially corrugated or pleated wall, (b) at least four plates, each plate having a central opening therein defining an edge inwardly of the outer peripheral edge thereof, said plates being arranged in superposed relation with adjacent plates secured along their inner and outer edges alternately, or (c) a pair of rigid platelike members pivoted together along a portion of their peripheral edges, the remaining peripheral edge portion of said plates being joined together by a flexible member which is pleated in some position of relative pivotal movement of the platelike members.
