John Jeffries, a colonial physician, is known for his balloon flight across the English Channel with Jean-Pierre-Françoise Blanchard in 1785. Their first major ascent, on Nov. 30, 1784, was a notable event in London, observed by the Prince of Wales and the Duchess of Devonshire. Jeffries' aim was to conduct a scientific study of the atmosphere, for which he used a thermometer, barometer, electrometer, and hygrometer (not to mention a compass and telescope for navigation). He also carried several bottles filled with distilled water, which he emptied at different elevations and then closed with glass stoppers to capture air at those levels. Twelve observations of temperature, pressure, and humidity were made. The experiment, suggested by Henry Cavendish, provided the first scientific data on air from sea level to more than 9,000 feet. Results from the chemical analysis performed by Cavendish correspond to currently accepted values.
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