286 MANAGEMENT OF THE ATMOSPHERE. 



interior surface, but not always affecting seriously the internal 

 volume, except in carrying off the rising particles of heated air, 

 the greater portion of which is condensed by the cold air imme- 

 diately as it escapes from the house. The consideration which 

 refers to the escape of air in a deteriorated state, and the conse- 

 quent necessity of admitting a fresh volume in its place, does 

 not appear to offer any insurmountable difficulties to the belief 

 that the admission of fresh air in the months of winter is very 

 frequently carried to an injurious excess. Although plants, in 

 the process of their growth, and in the discharge of their vital 

 functions, abstract matters from the atmosphere around them, 

 there is nothing, even in this, to render the admission of cold 

 air in large volumes at all necessary. In considering the nature 

 of the atmosphere in its relation to heat and cold, its elastic and 

 all-pervading properties must not be lost sight of. Under any 

 circumstances, a considerable effect will be produced by the 

 external upon the internal atmosphere, by radiation alone ; and 

 with the evidence before us of the successful growth of plants 

 in situations so much closed up as in Wardian cases, we cannot 

 do otherwise than believe that the interchange which takes 

 place between the volumes by these causes is sufficient to secure 

 the health and vigor of the plants, so far as the admission of 

 air alone is concerned. If it be argued that deterioration will 

 take place by means of evaporation from flues, or pipes, or any 

 substances confined within the structure, or from the decomposi- 

 tion of organic matter, the same fact is presented of an inter- 

 change continually going on, and is sufficient to meet the case, 

 so far as to show, that, on this ground, at least, the admission 

 of external air in large volumes is not essential. Besides, with 

 proper management, the gases that are generated by artificial 

 heat, or by the decomposition of substances which should find a 

 place in .hot-houses, may be combined with others having an 

 affinity for them, and thereby not only purifying the atmosphere 

 by preventing an excess of particular agents, but also turning 

 those agents to their legitimate purpose, and rendering them 

 beneficial, rather than detrimental, to vegetable life. And, 

 therefore, it can only be in cases where misapplication or gross 



