THE STORY OF NINE1EENTH-CENTURY SCIENCE 



with which the familiar phenomenon of the evaporation 

 of water was explained. 



Franklin had suggested that air dissolves water much 

 as water dissolves salt, and this theory was still popular, 



STRATUS CLOUDS 



though Deluc had disproved it by showing that water 

 evaporates even more rapidly in a vacuum than in air. 

 Deluc's own theory, borrowed from earlier chemists, 

 was that evaporation is the chemical union of particles 

 of water with particles of the supposititious element heat. 

 Erasmus Darwin combined the two theories, suggesting 

 that the air might hold a variable quantity of vapor in 

 mere solution, and in addition a permanent moiety in 

 chemical combination with caloric. 



Undisturbed by these conflicting views, that strangely 

 original genius, John Dalton, afterwards to be known as 



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