THE CONSTRUCTION AND HEATING OF GARDEN WALLS. 
THE CONSTRUCTION AND HEATING OF GARDEN WALLS. 
By Mr. P. WALKER, Gardener to H. Skkxne, Esq. 
^?0 horticultural erection is so generally met ■witli as garden walls, and nothing so frequently shows 
the want of proper care. Walls may be built either of brick or stone, as is most convenient in 
the locality. Bricks are generally preferred, but their superiority in radiating heat is not so great as 
to be worth incurring extra expense, for stones make a wall fit for all purposes required, if care be 
taken by the masons to make proper joints, and they are 
not permitted to fill up mth large seams of mortar, 
which fall out the first winter, leaving crevices capacious 
enough to shelter an army of insects, sufficient to eat all 
the fruit. The objects of a garden wall are specifically 
twofold: first, protection from radiation during the ab- 
sence of the sun, by which excessive cold is avoided. Dr. 
Wells's experiment on dew illustrates this. A thermo- 
meter, protected by a handkerchief held horizontally, was 
found, by repeated experiments, to be from 4 to 6 degrees 
higher than one openly exposed on a grass plot. This 
is the conservative power of the garden wall, and it is 
one of great importance ; for the greatest radiation takes 
place dm-ing calm, clear nights, and may be so much in 
excess as to produce fi'ost ten months in the year in oiu- 
climate. The second object of the garden wall is accele- 
rating vegetation, by increasing the temperature of the 
atmosphere in which the tree grows. When the waU is 
heated by the rays of the sun, it, in common with all 
heated bodies, radiates its caloric in ratio to the square 
of its distance : thus, if at one foot fi'om the wall we have 
a power of 1 degree, at one inch we have a power of 144 
degrees. The reflection of all the imabsorbed rays of the 
sun, impinging on the surface of the wall, increases the 
temperatm'e of the atmosphere considerably. This power 
I will term forcing. That it may be as efiicient as cii'- 
cumstances wUl admit of, the coping must only project 
two inches over the top of the wall, that it may not 
prevent the rays of the sun falling on the trees, but at 
the same time be sufficient to protect them fi'om rectilinear 
radiation by night. 
The conservative power is often aided by canvas, nets, 
straw, or spruce fii' branches. Of these, canvas spread by 
night, and removed by day, is the best, for increasing the 
forcing power, which is imperatively necessary for Peaches 
and Nectarines, in cold, cloudy seasons, when they make 
late growth, are badly ripened, that is, they are un- 
productive next year, which often ends in the total des- 
truction of the tree by canker. If the wall is fined, and 
fii-e heat is introduced by smoke, these flues ai'e unfortu-. 
nately found in practice too difficult to clean, and con- 
sequently di'aw badly when damp or foul, from theii' great 
length and necessarily tortuous course. Hot water pipes 
have been used with better efiect; but the expense in 
procuring and fixing them, has prevented theii' use in a 
general way. 
The method of heating that I recommend, with hot 
air, is one which may be effected at no more expense than fiues ; and — however doubtful may be the 
propriety of introducing aii-, deterioted by passing over a highly heated surface, for the sujiply of 
animal and vegetable organization, in tliis case, — it can be productive of no evil, being merely 
introduced into the interior of the wall. In height, the wall should not be under eight feet, from 
SECTION OF A HOT AIR STOVE-CHAIMBER, AND 
FLUES FOR HEATING A GARDEN WALL, 
w, Furnace. 
6, First iron plate on wMch tlie fire acts. 
c, Second iron plate. 
d, Brick arch. 
e, Air liolcs, opening into the hot air chamber. 
/, Hot air chamber. 
//, Flue, communicating between hot ail" chamber and 
flues h, Ii, &c. 
7i, Flues in the interior of the "wall. 
?', Door to slide open when it is desirable to accelerate 
the circulation of the air. 
/.', Soot door and damper. 
I, Door for removing dust from the bottom of the hot 
ail" chamber. 
Tlie heating apparatus, being placed below the gi'ound 
level of the wall to be heated, is, as much as is prac- 
ticable, situated at the lowest point of the ground level 
of the wall. The furnace is bricked, (w, m.) that a 
supply of the coal may be coked, thereby reducing the 
consumption of fuel, and lessening the attendance re- 
quisite. The air in contact with the plates h, c, being 
expanded by heat, will flow into the chamber/, coming 
into contact with colder air there, it will acquire a rota- 
tory motion, retaining a tendency to ascend in ratio to 
its rarefaction, and, in consonance with which tendency, 
it will flow along the flues /;, as indicated b}' the arrows. 
When the heated air- is found to circidate sluggisldy, in 
consequence of its peculiar electric condition, sliding 
open the door /, will accelerate its circulation. 
I 
