C8 



to the passing air. The consequences such winds 

 bring upon vegetation is well known to be destruction 

 of its foliage, and, in many instances, death. Air at 

 rest, as in a hothouse, does not absorb moisture so 

 rapidly as air in motion ; therefore if the whole area 

 of its floor was a tank of water, the air confined within 

 the house would never be so saturated with moisture 

 as air at the same temperature passing over water, 

 moist earth, and vegetation, as in the ordinary course 

 of nature. To obviate this, gardeners promote the 

 diffusion of watery vapour through the air of their hot- 

 houses, by placing pans of water upon the flues, by 

 having open gutters of hot water within them, and by 

 even admitting jets of steam. The difficulty attend- 

 ing all these processes is to have the amount of vapour 

 in a natural proportion to the temperature of the 

 house. A little inequality is not of much consequence, 

 but, other treatment being correct, the nearer to the 

 dictate of nature, so much nearer will the plants be 

 to a state of best vigour. 



A consequence of air being duly impregnated with 

 moisture is, that evaporation of water from a given 

 surface exposed to that air proceeds slowly, shown by 

 its causing but little cold. This is demonstrated by 

 the following registries of thermometers, kept at Cal- 

 cutta, during some of the months of 1841 and 1842. 

 In June, August, and September, the air there is 

 saturated with moisture. In December, January, 

 and February, it is driest. 



