A low-temperat ure patch Lest for sounding· balloons is described. In t hi s Lest a cil·eular piece is cut out of the rubber film , clamped around its circumference, and inflated un til it bursts. Equations applying to the patch test and to the flight of soundin g balloons arc dev eloped. Th e important properties in determining the flight elevation are found to be the flaccid length of the balloon and the elongatiQl1 ciJ the rubber film. The effecti,·e elongat ion is defined as the average

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... gation of the e ntire balloon film at t he pressure at which Lhe "·eakest part of the balloon will fail. A me thod of estimating this effective elongation from patch test data is given. Correlation was found between patch-test data and nighLflight elevations. On the basis of fl ights made with thennistors both inside and oulside t he balloon , the te mperature of the balloon film at burst is estimaLed to be 0 to 4 Celsius degrees colder than t he surrounding air at night and 20 to 30 Celsius degrees wanner ·than the s urrounding air in Lhe daytim e.