MANAGEMENT OF THE ATMOSPHERE. 285 



The admission of cold air as the sole or principal agent in 

 regulating the internal temperature of a hot-house during win- 

 ter, seems to be perfectly unjustifiable. There are, indeed, 

 times when it can hardly be avoided, during the application of 

 artificial heat; but these are exceptions, rather than the rule. 

 Heat, when applied in early forcing, or to maintain the temper- 

 ature of plant-houses, is artificial, and, therefore, so far unnatu- 

 ral. And it appears still more unnatural to apply more than is 

 necessary, for the purpose of admitting the external to cool 

 down the internal atmosphere, without having secured any 

 equivalent advantage, but rather lost, by the change. It is much 

 more reasonable, as well as economical, to apply as much heat^ 

 and no more than is necessary, to raise the temperature to the 

 minimum point, or, at least, as near this point as is possible. It 

 may be supposed that it would be unsafe to keep the tempera- 

 ture so close to the minimum point, lest the sudden external 

 changes, to which we are subjected in this country in winter, 

 might have an unfavorable effect upon the internal atmosphere ; 

 and, under certain circumstances, this would be the case, — such 

 as an imperfect heating apparatus, a badly glazed house, or a 

 want of skill in the management of it. The necessity of main- 

 taining the minimum rather than the maximum temperature 

 has been already adverted to in the preceding chapter ; and, 

 instead of being the exception to a general rule, it is rapidly 

 becoming the rule itself. We must consider that the object to 

 be kept in view is to improve upon the means at present in use 

 to obtain these results, and to obviate the risk and inconvenience 

 which might otherwise ensue by their adoption. It will be 

 observed, that it is not when the mild and genial weather of 

 spring is experienced that these remarks have any forcible 

 eflfect, but when the outward elements are unfavorable to the 

 development of vegetable life. 



2. The atmosphere of a hot-house is very much influenced 

 in winter by the glazing of the sashes, and the adjustment of its 

 various parts. When the laps of the glass are open, there is a 

 continual egress and ingress movement in the atmosphere adja- 

 cent to the apertures, extending generally over the whole of its 



