James Pollard Espy

Today is the birthday of meteorologist James Pollard Espy, born in Pennsylvania in 1785. After attending college he practiced law and taught classics before taking an interest in atmospheric science. Espy is best known for being ahead of his time in grasping the thermodynamics behind the formation of clouds and storms. In his 1841 book Philosophy of Storms, he laid out the basics of atmospheric convection, including the expansion and cooling of air as it rises and the importance of latent heat released when water vapor condenses to form clouds. In 1842 Espy was appointed the first official meteorologist of the US government. In early 1843 he produced the first series of US weather maps, including the one below. Espy later used the telegraph to compile various meteorological observations. Perhaps overconfident in his understanding of storm formation, Espy proposed setting forests ablaze to trigger rainstorms. Congress wisely passed on his proposal.

Date in History: 9 May 1785