early 13c., aspy, from Old French espier (12c., Modern French épier), from Vulgar Latin *spiare, from a Germanic source (cf. Old High German spehon "to spy;" see spy). Related: Espied. For initial e-, see especial.
American meteorologist who is credited with the first correct explanation of the role heat plays in cloud formation and growth. His use of the telegraph in relaying meteorological observations and tracking storms laid the foundation for modern weather forecasting.