A brief description is given of a new refrigerated expansion chamber apparatus based on an Australian C.S.I.R.O. design for measuring ice nuclei concentrations. The compatibility of results between five instruments of similar construction, a comparison of data obtained with a simple version of the mixing chamber method, and homogeneity of rapid expansion measurements at sites 8 and 100 miles apart are investigated. Except for uncertainties regarding the extrapolation of results to natural clouds, all indications are that, with care, the nucleation level in the atmosphere is capable of objective, compatible measurement with standardized equipment. However, a series of measurements verified the existence of significant differences between the rapid expansion and mixing chamber techniques. Both methods reflected similar trends during appreciable increases or decreases in nucleation activity. A surprisingly uniform geographical distribution of aerosols responsible for ice crystal nucleation is suggested in some of the results.