22 



On the apparent Changes 



to seventy miles high. The principal accumulations of vapours, 

 are indeed considerably short of this height, and being upon or 

 near the surface, their strata may in effect be considered as of 

 various horizontal diameters from 12, to 24, to 30, miles long, 

 as they may be estimated to be of the height of one, two, or 

 three miles. 



