the Ramsauer-Townsend minimum in the momentumtransfer cross section. Hence, the total cross section in the neighborhood of the minimum is given by the P-wave phase shift while the momentum-transfer cross section is approximately given by the difference between the P-and D-wave phase shifts. Therefore, one would expect the minimum momentum-transfer cross section to lie deeper than the minimum total cross section. The fact that the results of Frost and Phelps 16 did not find such a deep Ramsauer-Townsend minimum must be attributed to their necessarily broad distribution of electron energies.In the case of argon, where there is a strong energy dependence of the cross section, it is quite clear that a much better measure of the momentum-transfer *