"The performance of the Model I electrostatic precipitator sampler in recent field and laboratory tests is described and discussed. Two of the four precipitator-bearing balloon flights during this interval reached the floating altitude of approximates 105,000 feet, and the precipitator operated efficiently on both. One sample was collected at the nominal design flowrate of approximates 100 cfm, and the second at approximates -200 cfm. Comparison of the deposition profiles of the stratospheric samples with those obtained under controlled conditions in the altitude chamber indicates that the field samples were collected with >90% efficiency. The laboratory tests also showed that the performance capability of the precipitator improves with increasing precipitator current, and with increasing altitude. One of the above balloon flights carried two Model A-I altimeters with recorder outputs. The two records were identical within plus or minus 250 feet. In addition, variations in altitude indications were consistent with the less sensitive aneroid barocoder measurements from the same flight. A revised Model A-I altimeter with a telemeterable output signal has been designed and constructed. The frequency of the signal is a function of the altitude. A preliminary design concept for a flowmeter with negligible flow resistance is described. It would utilize …