44 
THE FLORIST AND POMOLOGIST. 
[ February, 
The result of grouping glass walls together, or forming them into gardens, is 
a clear gain over brick walls of from 2° to 5° in favour of glass. Possibly the 
thickness of the glass (rough plate weighing about 2£ lbs. to the square foot) has 
a good deal to do with this superior temperature. The dryness- of the wall, and 
the impossibility of any moisture penetrating its substance, or clinging to its 
smooth, glossy face, may have more. There is yet another reason for the genial 
temperature of glass gardens. Both sides of the wall are heated to nearly the 
same degree, and the earth on each side is heated also; they have two south 
North. 
walls and two south borders, instead of one only, as is of necessity the case with 
opaque walls. It is well known that the north side of these, and the ground 
also, is intensely cold ; the contrast is great, the interval between very small; 
the heat and the cold almost touch each other, being only 9 in. or 14 in. apart 
at the most. 
Nature is ever working to an equilibrium of temperature. To this end heat 
speeds on restless wings (I do not affirm that it is material) for evermore. By 
night and by day the contest rages around every opaque wall, on which one side 
Fig. 2. Ground Plan, with cross walls E. and W. FiG. 3. Ground Plan, with diagonal walls. 
is colder than the other. The combatants are heat and cold, or rather more 
heat and less heat. No quarter is ever asked or given, no armistice signed 
between them, neither is an absolute victory obtained by either side; and yet 
the result is far from nil. It is that one side is not so cold, and the other is not 
so hot, as either would have been apart. It is this near proximity of a cold wall 
and a cold border that depresses the temperature on the south side of walls. 
The policy that heats one side at the expense of the other is something like 
keepin g a fire at one end of our rooms and a large heap of ice at the other. The 
i 
