THE COTTAGE GARDENER. 
October 20. 
43 
bottom, and were then pressed down firm on the pipes. 
When the pipes were heated, the putting your hand 
inside the pans would enable you to tell which was 
solid and which was hollow. When the pans wore 
filled with water, the solid - bedded ones evaporated 
themselves to dryness three and four times for the 
hollow ones doing it once. I, and many more, place 
such pans and earthenware vessels on pipes and flues 
merely in a moveable state; but we are well aware that 
evaporation does not proceed in an equal ratio it would 
do when joined without cavity to tho heating medium. 
Confined air, therefore, is a first-rate non-conductor of 
heat—a fact, which, neither in gardening nor social 
economics, has taken that place which its importance 
demands as a security against extremes either of heat 
or of cold. Now to proceed. 
3rd. “ 1 have two pieces of ground, about twenty feet 
wide, some forty feet long; one lying cast and west, the 
other north and south. 1 wish to devote that space to a 
pit or pits, to keep plants, propagate plants, and force 
them a little in spring, with little or no fire-beat, with 
such assistance as the refuse of the garden, the drop¬ 
pings of a cow, and the famous “ gardener’s pony" can 
afford, with the addition of some trusses of bad hay to 
the usual covering in bad weather, as fuel has to be 
brought a great distance. Now, whether I have a pit or 
pits, I must have room out of this space for a dry, com¬ 
fortable path all round them, for walking on, examining 
the interior, taking off sashes, &c. Bricks are far to 
drive; I wish to cover some ten or twelve feet in width 
with flags, and I wish to do it as economically as possi¬ 
ble. As respects future covering, &c., I had thought of 
a double-roofed pit, what you call span-roofed, but then 
I see that you, and Mr. B., and Mr. C., and Mr. F., and 
Mr. S., have nothing of the kind, only five or six feet 
wide pits, each, of course, with its high brick wall at 
back. Now do solve'my difficulty?” The above is the 
purport of several communications. The first reply is, 
not to be guided by what we may have done. Where 
utility, and first expense in covering a certain space are 
the objects, the span-roof, even in pits, will take the 
place of the one-sided sloping-roof, because, supposing 
a wide span-roofed pit to hold the same amount of ma¬ 
terial as the narrow pits, the expense of the two high 
back walls is nearly dispensed with; you haviug merely, 
instead, a few supports from the centre, and a ridge 
board, &c., for the rafters and sashes to work against. 
Bear in mind, however, that no one system of build¬ 
ing or enclosing with glass will present you with 
every advantage. For instance, lately, double glass 
walls, enclosing but a narrow space, wore to be 
the panacea for most of the evils attendant upon 
half-hardy plants and fruits; were to finish the lean- 
to-shed-like-houses, and do away with the necessity for 
covering, &c. Now, without any practical working of 
the buildings in question, yet reasoning from analogy, 
and leaving out of view the expense of such houses— 
itself a very great consideration for the space they 
occupy—we could not but conclude that the chief dcfcuce 
they exerted against cold was owing solely to the dryness 
and stillness of the air within ; and that instead of being 
independent of heating, or covering, in severe weather, 
they were much more dependent upon one, or both means, 
than a common lean-to narrow house; inasmuch as they 
contained but little amount of air, and nothing of an 
opaque body for obtaining and then giving out heat, as 
the back of a house, or pit, exposed to the sun during 
the day, would continue to do until the wall became as 
cold as the air surrounding it. Hence, when we build 
a span-roofed-liouse for plants, we do so, first, that our 
plants may have light all round them, and not be drawn 
to one side merely ; and then, again, because, if we ob¬ 
tained the same amount of light from the. same quantity 
of glass on the lean-to system, we should be obliged to 
build a high wall for its back, instead of a short one all 
round for a span-roof; but we never think of managing 
such a span-roofed-bouso without more of a heating or 
protecting power than would bo necessary for the same 
quantity of glass stretched out along the side of a wall, 
merely because the wall is both an absorber and a 
radiator of heat, lienee it is that established gardeners, 
who are getting the chance, as at Woburn and else¬ 
where, whether for fruit or conservative walls, arc adopt¬ 
ing the model of the narrow upright houses at Trentham. 
Keeping all this in view, not forgetting what was 
said at page 8, about shallow pits, and deep pits, and 
well aware that deep or shallow, more care must be ex¬ 
ercised against sudden extremes in a wide span-roofed 
pit than in the same amount of glass, with its upper 
end against a wall; still, in the circumstances and 
premises alluded to, as to ground, bricks, space, ex¬ 
penses, &c., I would decide upon a span-roofed pit, and 
on the ground running north and south, that is, with 
the two sides facing east and west, or nearly so, and 
the two ends north and south; the latter being of glass, 
and the former either of glass or an opaque substance. 
Supposing your pit to be thirteen feet, outside measure, 
you will then have a path of three-and-a-half feet all 
round it, which, in general, will be quite sufficient. 
The sashes may slide up and down in the usual way. 
lu extreme cases, a sash would require to be taken off 
when anything particular was doing. For all common 
purposes, such as watering, &c., each sash as come to, 
could be held upright, by tilting it with a moveable 
triangle, formed of two pieces of wood long enough, 
joined at an acute anglo, and an iron point inserted 
there to suit a hole in the lower part of the sash so as 
to keep it steady. A cross-bar would keep the base of 
the two pieces from spreading. In the case of such a 
pit, where covering is to be the chief means employed 
for counteracting cold, the ridge should not be more than 
from two-and-a-hall' feet to three-and-a-half feet above, 
though if shutters are adopted for covering, at night 
rise six inches more, if particularly desired. Supposing 
that the side walls are from nine to twelve inches above 
the ground level, from two-and-a-half to two-and-tlnee- 
quarter feet high at the ridge would be sufficient for 
keeping half-hardy plants, and three feet would be a 
security from tender things being injured by the damp 
clinging to the glass. Four feet, in such a case, would 
only be required when growing plauts or fruits that 
needed a good amount of sunlight in spring and autumn. 
Provided there was nothing to obstruct the rays, sink¬ 
ing the wall in front six inches would just have the 
same effect as raisiug it behind as much. 1 have fre¬ 
quently covered long sashes when their upper end was 
more than six feet from the ground, but such a mode 
can be adopted in a span-roofed pit only when you had 
a good heating apparatus to fall back upon. 
“ Then what shall I cover such a pit with — mats ? 
I see you use them.” No ! for one twelvemonth I 
question if they are not the most expensive; if you 
take any half-dozen of years they will beat anything 
and everything for dearness. Those, however, who 
must give an annual sum, and nothing more, will be 
forced to continue to give commerce to the Russians. 
In such a caso as your’s you could do nothing with 
them except fastened to a frame, the size of a light, and 
with laths or rods on the light, for the protecting frame 
to slide up and down upon. Asphaltfelt, Frigidomo, 
strong waterproof, or tarred calico, would all beat mats, 
because waterproof; and dryness on the glass are great 
things. Some, for such places, have strong cloth on 
rollers, or a canvass covering, as if for a light waggon; 
but the evil of all these latter is, that in bad weather 
they will freeze when oil', be torn in pulling them out, 
or with a hard piece give the glass a whip, to see which 
was hardest. Everything considered, had 1 such a place 
