128 Mr, Daniell on Climate. [Feb. 



of Horticulture. When it is considered that a temperature at 

 night of 20° is no very unfrequent occurrence in this country, 

 the saturation of the air may upon such occasions fall to 120°, 

 and such an evil can only at present be guarded against by 

 diminishing the interior heat in proportion ; but whether we run 

 upon Scylla or Charybdis is no very desirable choice. 



By materially lowering the temperature we communicate a 

 check which is totally inconsistent with the welfare of tropical 

 vegetation. The chill which is instantaneously communicated 

 to the glass by a fall of rain and snow, and the consequent eva- 

 poration from its surface, must also precipitate the internal 

 vapour, and dry the included air to a very considerable amount, 

 and the effect should be closely watched. I do not conceive 

 that the diminution of light which would be occasioned by the 

 double panes would be sufficient to occasion any serious objec- 

 tion to the plan. The difference would not probably amount to 

 as much as that between hot-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 possibly 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 objec- 

 tionable, upon the same principles which I have been endeavour- 

 ing 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 

 foUage. 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 warming 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 shown them that 

 many kinds will not succeed under any other treatment. The 

 end of this is obviously to preserve a saturated atmosphere ; 

 and it affords a parallel case to that of Dr. Wells of the antici- 

 pation of theory by practice. 



The effect of keeping the floor of the hot-house continually 

 wet has been already tried at the Society's Garden, at my 



