Abstract: Method for measuring the propagation velocities of ultrasonic acoustic waves through rock fragments which includes the steps of (a) introducing the fragment in a coupling fluid between a pair of piezoelectric transducers capable of generating highly damped ultrasonic acoustic waves; (b) passing highly damped ultrasonic acoustic waves through the fragment, said waves being generated by a pulse generator with a pulse width varying from 0.1 .mu.s to 20 .mu.s; (c) visualizing the obtained electric signals by an oscilloscope with a resolution of at least 10.sup.-2 .mu.s; and (d) measuring the transit time of the waves themselves. The ultrasonic acoustic waves may be compressional or shear waves. In one embodiment the coupling fluid has a viscosity varying be 200 and 800 poises.