Abstract: A method of and an apparatus for determining sound propagation speed in a medium which is subject to variations in this speed. A measuring tube containing the medium is energized by a loudspeaker (ultraacoustic transducers) with a controllable energizing frequency in resonance with the measuring tube containing a column of the medium to be evaluated. The resonant output frequency is detected and modulated with a low frequency signal and the mean value of the modulated output signal is formed and counted. For a predetermined count, the elapsed time is measured and from this value the propagation velocity is calculated.

Abstract: A device usable in firearm practice comprises an upright target member with a front surface having selected heat-emitting areas which simulate the thermal signature of a military object. That surface is covered in one instance by two interleaved arrays of conductor strips bridged by short patches of resistance material which act as localized heat generators upon being energized with direct current. In another embodiment the heat-emitting areas are reflectors irradiated by infrared lamps that are disposed in front of the target member below a firing line.

Abstract: A target for a rifle range has an upright with a rectangular opening adapted to be alternately occupied by two sheets carrying different target images. The sheets may be mounted back-to-back on a common support, such as a swingable frame, or may be interconnected to form an endless band led around rollers. The mounting frame can be internally equipped with electroacoustic or other sensors to serve as an impact-detecting chamber.

Abstract: A target device for ascertaining the proximity of a hit to the target center comprises a plurality of transducers separated from one another in a space behind the target surface and positioned to respond to the impact shock at times determined by the sound propagation velocity in the air of this compartment. To increase the accuracy of the device, means is provided to provide an essentially constant temperature gradient (or uniform temperature) in the space or compartment and/or one sensor more than that required for determining the position of impact when the sound propagation velocity is known, is used.