CELERY. 37 



is raised, and of course must lose it when- 

 ever that temperature is suddenly reduced. 

 Thus there is much more water in the air 

 at noon on a hot July day, than on one in 

 November when we can scarcely see a 

 dozen rods through the thick mist. Rain 

 is produced in this manner, by the sudden 

 condensation of watery vapor, and dew 

 by the contact of warm moisture-laden 

 atmosphere with the cold ground. 



In the hot-bed the same law holds 

 good. The moisture which we have 

 added to the soil is heated and eva- 

 porated by the heat above and the heat 

 below, and as the glasses of the sash are 

 several degrees cooler than itself it is 

 forced to deposit in beads, as above 

 stated. 



