The problem under discussion is the velocity of ultrasonics in liquids, specifically water, at various temperatures and high pressures. This report deals with the apparatus, and with some representative results obtainable with it.The electrical apparatus makes use of a presentation unit (Dumont 256 or A/R 'scope) which synchronizes the sequence of operations by internally generated trigger signals at low repetition rates. Three‐ to five‐microsecond pulses at controllable amplitude and approximately 15 Mc/sec carrier frequency are imposed on an X‐cut quartz crystal which has been placed inside a pressure‐supporting vessel containing the test sample. The resulting ultrasonic pulses in the liquid are reflected back and forth over a definite path length between the transducer and a mirror. After amplification in a receiver strip the complete echo‐pattern becomes available for visual comparison on the presentation screen. The timed relative delay (and the measurable amplitude differences) between successive pulses furnish data for velocity (and attenuation) measurements when certain corrections are attended to.Representative data are given for the velocity in water (to 0.1 percent) as a function of pressure to about 6000 atmospheres. From the data on water, information is derived on the temperature coefficient of sound velocity and on the ratio of specific heats at increasing pressures. The latter results are compared with those obtained directly from purely static experiments, and the advantages of the ultrasonic measurement technique for the derivation of some of the thermodynamic coefficients are cited.