On the Prodtiction of Vapor. 77 



form, till we come to the surface ; where there appears 

 to exist a stratum of water of a small insensible depth 

 so rare as to be nearly in a state of vapor. ' 



The arguments and inductions from phenomena that 

 conspire to prove the existence of this cause, are the fol- 

 lowing: 1st. Water is of an elastic compressible nature ; 

 therefore at the surface, where the attraction and pres- 

 sure are the least, it will be more rare than at any assimi- 

 able depth below, where the attraction and pressure are 

 stronger, and consequently the water more dense. 2d. 

 The affinity that exists between the particles of water 

 among themselves, and also between the particles of wa- 

 ter and caloric, is very strong ; and vastly stronger than 

 that between the particles of air, or that between air and 

 caloric. If there were not a powerful attraction between 

 the particles of water, when a strong heat is applied, the 

 whole body of it would undergo a simultaneous expan- 

 sion like air, and be dissipated in vapor at once. And 

 if caloric did not possess a stronger attraction for water 

 than for air, it would abandon the particles of vapor to 

 unite with the air ; hence the position is evident. 3d. 

 The force of attraction between the particles of water is 

 such, that when the whole cause is applied, the contrary 

 force of heat is but just sufficient to balance it ; this is 

 apparent from the small degree in which water is capable 

 of being compressed. 4th. Hence it will follow as a con- 

 sequence, that water will soon attain to nearly a uniform 

 density. For a particle is attracted not only by the one 

 next to it, but by several adjacent ones. But at the sur- 

 face, on account of the absence of the particles above, 

 they will be less attracted, and consequently will range 

 themselves at a greater distance ; there will therefore be 

 a stratum at the surface, much more rarefied than water 

 in its common state. This rarefaction will be surpriz- 

 ingly increased by the investiture of caloric, which the 

 particles of water are then in a situation to assume. At 

 any sensible depth the affinity of aggregation is so strong, 

 that it squeezes out and excludes the caloric ; which 

 will nevertheless, for the reasons before mentioned, be 

 retained at the surface. This also accounts for the cool- 

 ing process in evaporation. As fast as the matter of heat 



