Experiments on Atmospheric Evaporation until the End of the Eighteenth Century

Abstract

The importance of the loss of water due to evaporation was first recognized during the Hellenic period.1 For example, the historian Herodotus of Halicarnassus (484-425 B.c.), who considered all knowledge to be within his jurisdiction and pursued with great enthusiasm his inquiries into a host of different things, was fascinated by the River Ister (Danube), which remained at the same level during summer as well as winter. The reason, explained Herodotus, was not very difficult to find. The Ister flowed at its natural height during winter as there was scarcely any rainfall in that period-only snow. The extra water brought to the river during summer, due to both melting of snow and rainfall, was counterbalanced by the greater power of attraction of the sun, and, consequently, the flow in the Ister remained at the same level as in winter.2 It should, however, be pointed out that his phraseology that the sun attracts or draws the water was probably a metaphorical term intended to denote some more general and abstract conception than that of the visible operation which the word primarily signifies. This abstract notion of 'drawing' is, in the historian, as we see, very vague and loose; it might, with equal propriety, be explained to mean what we now understand by mechanical or by chemical attraction, or pressure, or evaporation.3 Later, the Roman architect Vitruvius was worried about the loss of water due to evaporation and suggested that the aqueducts should be arched over4 to practice water conservation. These ancient