76 On the Production of Vapor, 



the gravity of the atmosphere is increased, it prevents 

 the rise of vapor by its pressure upon the water, it might 

 be repHed, 1st. That the presrsure is not such as to pre- 

 vent even a small force from agitating the surface of the 

 water, and if it is incompressible, and alway of the same 

 density, no reason can be given, why an equal force should 

 not dislodge as many aqueous corpuscles at one time as 

 another, 2d, In water, a body will ascend with the same 

 facility at the depdi of an hundred feet, as at one ; and if 

 an increased pressure alters not the tendency of a body 

 to ascend in water, it cannot in air. 



The diiference in the heights of the several strata of 

 clouds observed by the gendeman at Pepperell, cannot 

 easily be accounted for, on known principles. For as 

 the gravity, and consequently the pressure of the atmos- 

 phere that morning was gradually decreasing, the vapors, 

 ivhich arose at the several times observed, as far as that 

 cause had influence, would all gradually and equally ex- 

 pand ; and would eventually ascend to an equal height. 

 And as the heat was continually increasing, we should 

 conclude that the column of vapor which arose last, 

 would be more rarefied, and take the highest station, 

 contrary to what was observed. 



To account for these phenomena, it seems necessary 

 to unfold some other principle ; and from the several ap- 

 pearances that attend the formation and ascent of vapor, 

 it is probably this ; that water is in a small degree com- 

 pressible. The contrary doctrine has been held by phi- 

 losophers. But the experiments of Canton have proved, 

 that the commonly received opinion is erroneous. He 

 inclosed water in spherical glass vessels, from which a 

 narrow neck proceeded, like that of a thermometer, the 

 water was found to occupy a larger space when the pres- 

 sure of the atmosphere was removed by the air-pump, and 

 a less space when a greater pressure was added by the 

 condenser. If water is compressible, it follows, that like 

 the atmosphere, it has a variable density, decreasing 

 more or less, according to the degree of compressibility, 

 from the interior towards the exterior parts. In the at- 

 inosphere the density gradually decreases as we ascend 

 |rom the earth. But in water the density is nearly unl^ 



