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that the instruments were 'practical and reasonable in price,but a shortage of supplies for manufacture . .. will preventtheir extensive use until the termination of hostilities.'In 1950, four routine ascents were made daily at 5 am, 11am, 5 pm and 11 pm, as recommended by the WorldMeteorological Organisation. Balloons were not releasedwhen the base of the cloud layer was lower than 600 metresabove mean sea level.The balloon was inflated with hydrogen, and rose about500 feet a minute. A theodolite on the Observatory roof wasused to track the balloon. At night, a light was attached tomake tracking easier. Winds at 1 000 feet intervals weremeasured over two minutes (one minute before and oneminute after the balloon attained a particular height). Themethod was restricted by human visual range, and theballoon's rate of ascent was an estimate that could causecalculation errors.A daily meteorological flight from Kai Tak was institutedin January 1949. The observations of dry and wet bulbtemperatures made on these flights were the Observatory'sfirst attempt to measure upper air temperature and humidity.The flights — first by the Far East Flying Training Schooland later by the Hong Kong Flying Club - continued untilNovember 1949, when they were replaced with radiosondeascents.Radiosonde ascents:Radiosonde ground equipment to determine upper airpressure, temperature and humidity was installed in 1949.Obstructions around the launching site caused difficultiesin releasing the balloons, particularly when it was windy.In 1951, the new site was established at King's Park, about1 kilometre north of the Observatory.The first radiosonde ascent was launched in November1949. Combined radiosonde and radar wind ascents weremade routinely once a day from December 1949, usingArmy-operated radar equipment. In 1955, the Observatory119