242 Mr James Bewley’s Description of a Plant-house. 
portant is, that the outer sashes should fit close, so as to 
admit of no circulation of air between. I do not like 
moveable sashes for top ventilation in any house, and there- 
fore in mine I carry up the glass only to within one foot 
from the top of the ridge; above this are wooden shutters 
or panels for ventilation, and by a very simple contrivance 
they can be opened or shut. | 
Now, as to temperature. My fern-house being 60 feet 
by 48, with a mean height of about 16 feet, contains 46,000 
cubic feet of space; and there being a pair of 4-inch hot- 
water pipes running round it, the heating power is 430 feet 
of pipe, or about 1 foot of pipe to 100 of cubic contents, 
In a single roofed house, I do not think this heating power 
would do more than exclude frost in severe winter weather, 
but with the double roof, the thermometer rarely goes below 
48. I think I once sawit at 46. My estimate is that I 
gain 14 or 15 degrees of heat from the double roof. The 
loss of heat is very slow in cold weather; I think it would 
take three or four nights of severe frost to bring the heat of 
the house down from 52 to 48 ; and probably thirty-six hours 
to cause the same reduction were the fire to be left out 
altogether. With a single roof, this would be expected in, 
I think, about six hours. It is a great comfort to know 
that if, in any house I have, the fire was let out, or neglected 
in the depth of winter for a whole night, its contents would 
suffer no damage. The reverse effects are equally interest- 
ing,—the very slow increase of heat in warm weather. 
This has been a hot summer, yet the heat of the fern-house 
has never, that I am aware of, gone up to 70; with a single 
roof, and the same amount of ventilation, the house would 
run up to 80 or 85 in a single hot morning. There is: 
another interesting fact, and one of great importance in 
plant-growing: there is a steady uniform increase of tem- 
perature in the house according as we ascend from the floor, 
day and night. This arises from the non-transmission of 
heat through the roof. Thus, while I have native ferns and 
other temperate plants growing below, I have tropical plants, 
ferns, and palms, &c. growing on the higher portions of the 
rockwork. And while, in ordinary houses, we remove tender 
plants from near the glass in severe weather, the nearer I 
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