THE 



GARDENER'S MAGAZINE, 



JUNE, 1840. 



ORIGINAL COMMUNICATIONS. 



Art. I. On the Means of supplying Atmospheric Moisture to 



Hot-houses, including some Observations on the Use of Steam 



for that Purpose. By John Rogers, Jun., Esq., F.R.S. H.S., &c. 



To imitate nature in the production of artificial climates under 

 glass three things are necessary, heat, light, and atmospheric 

 moisture, each in its proper degree. The agency of the first 

 two has long been known and studiously provided, the latter is 

 less obvious ; it has only lately been recognised, and gardeners 

 have still to seek the best means of providing it. It is perhaps 

 the most valuable practical result of the cultivation of tropical 

 epiphytes, that they have directed our attention to the hygro- 

 metric condition of the atmosphere, and culture in general has 

 benefited. 



The causes whose constant operation renders our artificial 

 climates unnaturally dry are principally two; the condensation 

 of moisture on the glass, and the escape of heated and damp air 

 through the crevices of the building, its place being constantly 

 supplied by dry external air. A third drain of moisture formerly 

 existed in the absorbing surfaces of brick flues, which drank up 

 the moisture of the air in contact with them, and carried it off 

 with the smoke into the outer air. The very general use of hot 

 water in iron pipes has removed this nuisance, and we have now 

 only to contend with the two first mentioned. 



Some idea of the drain of moisture by the escape of heated 

 air, may be formed from the following considerations. The 

 capacity of air for moisture, that is to say, the quantity of water 

 which a cubic foot of air will hold in invisible solution, depends 

 upon its temperature, and increases with it in a rapid ratio. 

 It is doubled between 44° and 66°. The consequence is, that 

 every cubic foot of air which escapes at the latter tempera- 

 ture, carries off with it twice as much moisture as it brought 

 in. Where the difference of temperature is greater, the drain 

 becomes greater also : air entering at 44°, and escaping at 

 80°, carries off three times as much as it brought in, escap- 

 ing at 90° four times. Now the escape of air from our best- 



1840. June. u 



