226 
ON THE CLIMATE OF HOT-HOUSE>S. 
by the double panes, would be sufficient to occasion any very serious objection 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 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 objectionable, upon the 
same principles which I have been endeavouring 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, inasmuch as 
it acts with a rapidity proportioned, in a very high degree, to its motion. I would 
suggest, 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 obvi- 
ously to preserve a saturated atmosphere ; and it affords a parallel case to that of 
Dr. Wells, of the anticipation 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 own suggestion ; and it has been found that the 
plants have grown with unprecedented vigour ; indeed their luxuriance must strike 
the most superficial observer. To the human feelings, the impression of an atmo- 
sphere so saturated with moisture, is very different from one heated to the same 
degree, without this precaution ; and any one coming out of a house, heated in the 
common way, into one well charged with vapour, cannot fail to be struck with the 
difference. Those who are used to hot climates, have declared that the feel and 
smell of the latter exactly assimilate to those of the tropical regions. But there is a 
danger attending the very success of this experiment, which cannot be too carefully 
guarded against. The trial has been made in the summer months, when the tem- 
perature of the external air has not been low, nor the change from day to night very 
great. In proportion to the luxuriance of the vegetation, will be the danger of any 
sudden check ; and it is much to be feared, that, unless proper precautions are 
adopted, the cold long nights of winter may produce irreparable mischief. I am 
aware that a great objection attaches to my plan of the double glass, on account of 
the expense ; but I think that this may appear greater at first sight, than it may 
afterwards be found to be in practice. It is, however, at all events, I submit, a 
point worthy of the Horticultural Society to determine ; and, if the suggestion should 
be found to be effective, the lights of many frames, which are not wanted in the 
