LAWS OF HEAT. AIR. 105 



than its full quantity of vapour : we may often 

 cool an object 10, 20, or 30 degrees withou ob- 

 taining a deposition of water upon it, or reaching 

 the dew-point, as it is called. To have had such 

 a dripping state of the atmosphere as the former 

 arrangement would have produced, would have 

 been inconvenient, and so far as we can judge, 

 unsuited to vegetables as well as animals. No 

 evaporation from the surface of either could have 

 taken place under such conditions. 



The sizes and forms of clouds appear to depend 

 on the same circumstance, of the air not being 

 saturated with moisture. And it is seemingly 

 much better that clouds should be comparatively 

 small and well defined, as they are, than that 

 they should fill vast depths of the atmosphere 

 with a thin mist, which would have been the 

 consequence of the imaginary condition of things 

 just mentioned. 



Here then we have another remarkable exhi- 

 bition of two laws, in two nearly similar gaseous 

 fluids, producing effects alike in kind, but dif- 

 ferent in degree, and by the play of their differ- 

 ence giving rise to a new set of results, peculiar 

 in their nature and beneficial in their tendency. 

 The form of the laws of air and of steam with 

 regard to heat might, so far as we can see, have 

 been more similar, or more dissimilar, than it 

 now is : the rate of each law might have had 

 a different amount from its present one, so as 



