Edmund Halley

From HydroWiki

Edmond Hailey was an English scholar that lived from 1656-1742 and was one of the premier scientists to understand quantitative hydrology at the end of the 17th century to begin to understand basic hydrological principles of the hydrological principles. His experiments and theories helped better understand the phenomenon of evaporation from seawater. He also went on to calculate an estimate of the amount of water that flows from the Thames River into the Mediterranean Ocean and the amount of water that evaporates from the Mediterranean Ocean to help explain the hydrological cycle in a quantitatively manner.

He began his career as an astronomer (Halley’s Comet) and while on a research project in the mountains of St. Helena, England. He observed that a great deal of condensation in high altitudes was fogging up his glasses and the paper was unusable because it was absorbing a great amount of water even though there was not any mist in the air in a clear day. He concluded from this study that evaporation of water occurred when water was heated that the water atom would expand 10 folds, decreasing its mass to lighter than air, and allowing it to rise in warmer temperatures because warmer air could hold more vapor. Prevailing winds would carry this vapor into the mountains and then the water would be condensed in the lower temperatures and then flows down the hills and into the springs that feed into the rivers and then into the sea.

He defended his theory of the hydrological cycle that all the water that fills the springs and oceans comes from ocean evaporation through extrapolating his calculations to estimate the amount of evaporation that occurs in the Mediterranean Ocean. He did this by calculating the amount of water that evaporated from a pot in a certain amount of time and then correlating and estimating it to the amount of water that would evaporate from the Mediterranean Ocean. He then calculated the amount of water that the Mediterranean would receive from the Thames river and the estimated amount from the rest of the 9 major rivers that in the Mediterranean. He concluded that the amount of water calculated to evaporate from the ocean was significantly enough to supply the amount of water flowing into the rivers of Mediterranean Ocean creating an equilibrium water balance of the Mediterranean Ocean. This quantitative explanation of the water cycle by Edmond Halley was a huge step in the history of hydrology.

Figure 1: Portrait of Edmond Halley

Figure 2: Halley’s concept of the hydrological cycle

Sources: Biswas, A.K. “History of Hydrology.” Amsterdam, Pub North Holland, 1970. http://www.venusovergang.nl/images/plaatjes/parallax/edmund_halleybig.jpg http://www.jstor.org/view/00359149/ap020037/02a00040/5?frame=noframe&userID=80761892@psu.edu/01cc99332700501b50c8d&dpi=3&config=jstor