This is a preliminary description of a new method of determining absolute pressure which is based on the simultaneous measurement of length and ultrasonic transit times. This method has been used to determine the transition pressure of pure mercury at 0 °C at 7571·2±1·6 bar. It is particularly advantageous to use for calibrating secondary gauges such as manganin gauges inasmuch as it gives a highly accurate measurement of nonlinearities in such secondary gauges. The gauge calibrated in the present study reaches a maximum deviation from linearity of −11·6 bar at a pressure midway between atmospheric pressure and the 0 °C mercury melting pressure.

A multiple crystal holder for simultaneous ultrasonic measurement on several crystals is presented. Four figures are included to show-clearly how-it is assembled and how each component works.