Pulse-modulated ultrasonic waves (shear or longitudinal) in the 10–30 Mc range are transmitted down a fused silica rod, through a polystyrene or silicone one-quarter wavelength seal, and into the solid specimen. Phase comparison of waves reflected back and forth within the specimen yields values for velocities of propagation and elastic constants. Advantages of the method are: (1) the specimen need not be large to insure a fair degree of accuracy—a thickness of one-quarter inch is usually sufficient; and (2) the quartz crystal transducer initiating the waves is maintained near room temperature, thus insuring well-defined wave trains. Illustrative data obtained over a temperature range of 78° to 300°K for silicon and germanium single crystals and 1.6° to 300°K for fused silica are given. For the latter, a high loss is noted, with an indicated maximum near 30 degrees Kelvin.