24 



On Climate, fyc. 



houses with wooden rafters and lights, and those constructed 

 with curvilinear iron bars, two of which have been erected in 

 the Garden of the Horticultural Society. It might also pos- 

 sibly occasion a greater expansion of the foliage ; for it is 

 known that in houses with a northern aspect, the leaves 

 grow to a larger size than in houses which front the south. 

 Nature thus makes an effort to counteract the deficiency of 

 light by increasing the surface upon which it is destined to 

 act. 



The present method of ventilating hot-houses is also ob- 

 jectionable, upon the same principles which I have been en- 

 deavouring to explain. A communication is at once opened 

 with the external air, while the hot and vaporous atmosphere 

 is allowed to escape at the roof ; the consequence is, that 

 the dry external air rushes in with considerable velocity, and 

 becoming heated in its course, rapidly abstracts the moisture 

 from the pots and foliage. This is the more dangerous, in as 

 much as it acts with a rapidity proportioned in a very high 

 degree to its motion. I would suggest it as a matter of easy 

 experiment whether great benefit might not arise from warm- 

 ing the air to a certain extent, and making it traverse a wet 

 surface before it is allowed to enter the house. 



There is one practice universally adopted by gardeners, 

 which is confirmatory of these theoretical speculations, namely, 

 that of planting tender cuttings of plants in a hot bed, and 

 covering them with a double glass. Experience has shewn 

 them that many kinds will not succeed under any other treat- 

 ment. The end of this is obviously to preserve a saturated 

 atmosphere ; and it affords a parallel case to that of Dr. 

 Wells of the anticipation of theory by practice. 



