Abstract: A method is described for causing hollow glass spheres to implode on command while deep in the ocean, whereby to produce an acoustic pulse. Specific means for causing the spheres to implode are described. The invention is useful for seismic work.

Abstract: A method and apparatus are provided for inspecting vacuum-packed containers. The invention comprises automatically subjecting each container to be inspected to a predetermined force so as to cause each container to emit a click as a result of relative displacement of the container and its liquid contents, and determining whether the container has adequate vacuum by measuring the time interval between application of the predetermined force and the occurrence of the click. In a modification of the invention the pressure determenation is made by generating a signal having an amplitude that varies according to the intensity of the click.

Abstract: A free-fall underwater sampler comprises a pair of jaw members and ballast supporting containers in which the jaw members and containers are operated simultaneously and independently of one another. A safety mechanism is also provided for preventing premature closing of the jaw members and release of the ballast. Other features and advantages are disclosed.