1744-1819

American scientist and physician who was the first to make scientific observations from a balloon. Jeffries made two ascensions by balloon with Pierre Blanchard, the first in 1784 and the second in 1785; they were the first to cross the English Channel in this manner. On the first ascent, after reaching an altitude of 9,309 feet (2,837 m), Jeffries took samples of air for analysis and made other observations with a thermometer, a barometer, and other instruments.