Abstract: A mechanically amplified electroacoustic transducer system comprising an electroacoustic transducer having a vibrating element and an amplifier rod forming a probe extending from the transducer and in acoustically coupling contact with the vibrating element over a relatively small region thereof. The probe has a length which is approximately equal to the quarter wavelength or a multiple of the quarter wavelength of the acoustical energy generated by the transducer, the exact length of the probe being selected to provide optimum output from the system at a selected operation frequency of the transducer.

Abstract: The circuit comprises an elapsed time indicating meter and a silicon-controlled rectifier, used to supply power to the meter, connected in series across the circuit's first and third terminals. Additionally, the circuit includes a small resistor connected between the second and third input terminals, that is, connected in series with the a.c. device. This small resistor receives the current through the a.c. device and the voltage across the small resistor is indicative of the operational state of the a.c. device. A variable potentiometer is connected full scale across the small resistor and the variable voltage is amplified by a common-base transistor. This amplified voltage is both rectified and filtered, serving as the SCR's gate terminal input for triggering the SCR.The potentiometer is adjustable to allow the SCR to trigger in either one of two conditions.

Abstract: An arch forming structure comprising a flexible arch forming member centerpiece with hinged pairs of struts attached by hinges to each side. The hinged pairs of struts are hingedly attached to a base and collapse inwardly beneath the flexible member. Two tension line lengths are used to snap the hinged pairs of struts from the collapsed condition through dead center to an outwardly sloping position from which further movement is prevented by their central hinge. Two further tension line lengths are jointed to central portions of the hinged pairs of strut members and threaded through eye bolts on the underside of the flexible member and are tensioned by outward movement of the hinged pairs of struts to bend the flexible member into an arch.

Abstract: A collapsible arch forming assembly comprising a flexible member and two tension line lengths with one tension line length threaded through even number guides, counted from one end of the flexible member and the other tension line length threaded through the odd number guides. Tensioning the tension line lengths arches the flexible member into the arch and this may be done by a winch assembly or inserting spreader bars at the guides to deflect the free one of the first and second tension line lengths at that position. The spreader bars may be replaced by, for example, mechanical jacks or fluid pressure actuated jacks particularly for such applications as using the arch forming assembly as formwork upon which concrete is poured.