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Two models of acoustic micrometeoroid detectors were flown piggyback on several Canadian rockets, one of which was launched in the spring of 1963 and the others in the winter and fall of 1964 from the Churchill Rocket Range. The micrometeoroid detecting systems and the calibration technique based on the elastic impact of polystyrene spheres are described. The detector response is found to be proportional to m0.8vl.l. Responses recorded during six flights are presented and analyzed. The analysis is developed in detail to illustrate the uncertainties in interpreting the data and to establish qualitatively the accuracy of the results. Responses attributed to impacts of micrometeoroids are treated collectively. An average impact rate of 1.4/mz sec and a threshold mass of 10-11 g a t 30 km/sec are ascribed to the data. A high density of small particles is apparently indicated. Impact rates for successive 5-km intervals to a height of 167 km indicate a variation with height. Regions of increased activity, roughly double the average rate, are observed centered on the height intervals 145 to 150 km and 125 to 130 km. A region of slightly less activity exists near 90 km, and a sharply defined region appears a t the 105 to 110 km interval. T h e relative stability of all or any of these active regions has yet to be established.

A new technique for the collection of large cosmic dust particles from balloons is described. Two flights have been completed successfully. Preliminary results are given.

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