the requirement for equal i ty of the gas temperatures in the forechamber and in the meter ing volume (sensor). The condit ion for equi l ibr ium of the gas in communica t ing , differently heated volumes in the transition region is determined exper imenta l ly . The orif ice method for de termining gas stagnation temperatures is widely used in exper imenta l gasdynamies. Normally its appl icat ion is l imi ted to a cont inuum; the possibil i ty of using this method for rarefied gas experiments has not received adequate study. The purpose of this paper is to invest igate the use of the method in the transition and f ree-molecular regions. 1. The method can be explained as follows. The dependence of the c r i t i ca l discharge rate G. on the s tagnat ion tempera ture T O and pressure P0 for a gas with constant specific heat ratio n has the form [ i ]