Lesson xix.] EVAPORATION, &c. 109 



form, is sublimation. Evaporation is by them ge- 

 nerally applied to bodies in a state of humidity; 

 and precipitation is the falling down ot any body> 

 dry or humid, which has been held in solution ia 

 any other body. 



There are, indeed, few subjects of philosophi- 

 cal investigation that have occasioned a greater 

 variety of opinions than the theory of Evapo- 

 ration : as such a diversity of opinions yet exist, 

 it is almost next to impossible to advance one, 

 but what may be contradicted, and, in some 

 respect, refuted : however, be this as it will, 

 among the various theories I shall make use of 

 the following. 



Dr. Hamilton, late Professor of Philosophy in the 

 University of Dublin, supposes that Evaporation 

 is nothing more than a gradual solution of water 

 in air produced and promoted by attraction, heat, 

 and motion, just as other solutions are effected. 

 To account for the ascent of aqueous vapours 

 into the atmosphere, this ingenious author ob- 

 serves, that the lowest part of the air being 

 pressed by the weight of the upper against the 

 surface of the water, and continually nibbing 

 upon it by its motion, attracts and dissolves those 

 particles which it is in contact with, and separates 

 them from the rest of the water. And since the 

 cause of solution in this case is the stronger attrac- 

 tion of the particles of water towards the air, than 

 towards each other, those that are already dissolved 

 and taken up, will be still farther raised bv the at- 

 traction of the dry air that lice over them, and thus 



will 



