42 
THE COTTAGE GARDENER. 
October 20. 
it, that you, and other gardeners, do not act more 
upon the principle; as you seldom seem to have any 
such ventilators as you mention? ” Few gardeners that 
have seen or travelled much will think these low veil 
tilators of no importance. I should not be acting 
right, did I recommend one system I made to answer, 
when I had proved that another mode would answer 
with less trouble and risk. Amateurs should bear in 
mind, that there are but few gentlemen’s gardeners that 
can chop and change as to them seems fit. There are 
no drawbacks as to what is expected from a garden, 
quite the reverse; but taken as a rule, there are but few 
extras allowed in the way of changes and improvements. 
In building, therefore, as well as many other things, 
amateurs would act wisely in taking the advice of a 
good gardener in the neighbourhood, instead of im¬ 
plicitly building and working as he had done. If you 
would prefer imitating, instead of advising, as a general 
rule, you will act more safely in going to a prosperous 
commercial establishment, rather than a private one. 
The latter, as a rule, must make the most of circum¬ 
stances ; the former will make all circumstances give 
way to ultimate advantage and profit. 
2nd. “ My bricklayer says, that a Hue built in a nine- 
inch wall, of the size proposed, will neither stand nor 
draw, and will get choke full directly.” Get the furnace- 
bars fifteen or eighteen inches below the level of the 
bottom of the flue, and it will draw fast enough. With 
common fuel, the very quickness of the draught will 
prevent choking, though, of course, it will require 
cleaning at times. I have previously described such a 
small Hue running beneath the paved floor of a small 
house that answers admirably. If you had any doubts, 
however, put two bricks on edge, instead of one, ,aud 
then you would have a flue, four inches by nine, amply 
sufficient for anything. The weight above will keep 
the wall strong enough, if you do not strike it violently 
opposite the flue. I mentioned this flue in the wall, 
not as the best position, but as involving the greatest 
economy of space and materials in the circumstances. 
I have worked such many years ago. 
3rd. “ I should like such a flue amazingly, but if I go 
deeper than three feet for a stock-hole, J shall come to 
water, and even then a place that would hold a store of 
coals, arched, &c., would cost nearly as much as the 
bricks of the pit.” Raise your pit more above ground, 
and then there will be no necessity for a deep stock- 
hole, and thus you would escape, alike the presence of 
water, and the necessity of sinking a well or drain to 
take it away. But what necessity is there for having 
a place like a huge coal-cellar for such a pit ? A bushel 
or hall-a-bushel of fuel would be enough at a time ; and 
a small place, some four feet by three, would be quite 
large enough. A flap-door over it would keep it dry. 
A little concreting or tarring of the ground would render 
it more so. Large or arched stock-holes for such work, 
is as useless as throwing money in the Thames. 
4th. “ I cannot see how surrounding the fined part of 
such a wall with earth, with the exception of a cavity all 
round, is to prevent the flue heating the cavity and then 
the earth, instead of being directed principally to the 
interior; and, therefore, I propose following out your 
suggestions as to the cavity ; but having several holes 
to be opened or shut at pleasure, communicating with 
the op>en air, and then have several pipes, taken from 
this cavity, through the wall, above the flue into the 
pit, so that when I open the outside holes there will 
not only be fresh air admitted, but it will be dried and 
heated before it gets into the pit, and thus I shall gain 
the advantage of the heat of the outside part of the flue.” 
I have no objection whatever to the plan. Of course, 
on the plan proposed, whenever you allow the external 
air into the cavity, you do away with its non-conducting 
heat property. But you will gain a great advantage in 
dull, cold weather, in thus boing able to send a portion 
t of fresh air into the pit; and a very small lifting of the 
i sashes behind will be sufficient to put the air in motion, 
j In fact, if your sashes are not glazed at the laps, there 
will be little necessity, in muggy weather, to lift the 
sashes at all. You have thoroughly got the right end 
of the admission-of-air theory in all cases of forcing, 
&c.; and when, even in cold pits, there is a great 
difference between the internal and external atmosphere. 
In very particular cases, gardeners are now anxious to 
have the means of heating cold air before it is admitted 
among delicate plants in a hothouse, by bringing that 
air previously in contact with a heating medium. 
Wanting these means, air, at such periods, is given, with 
great care, only at the highest part of the house, and 
then chiefly after the reflection of the sun on the glass 
has rarified the air contiguous to it. 
Though I thus approve of your plan, it is no less true, 
that an air-tight cavity will very greatly retard the con¬ 
duction of heat. Confined air, in fact, is considered one 
of the best non-conductors. Hence, a hollow wall, air¬ 
tight on both sides, will be loss influenced by tempe¬ 
rature than a solid wall of the same thickness. In such 
a case, when the inside wall is heated by the sun, or 
artificial means, it is not cooled by transmitting its heat 
easily to the outside wall. And on the contrary, when 
that outside wall is cooled down by frost, it would be 
long before the inside wall was aflccted through that 
medium. Many years ago, I made some rough experi¬ 
ments to satisfy myself on this subject. In the case of 
walls, hollow, but air-tight, and in that of others, hollow, 
but the holes filled with non-conducting material, as 
sawdust and charcoal, I could perceivo little or no 
difference; but both were different as respects heat and 
cold when covered, when contrasted with a solid wall. 
I may mention another trilling experiment, as showing 
my young friends, as well as a large one, the non-con¬ 
ducting properties of confined air. Two small tin jugs 
were taken possession of. An old ope, a size larger, 
was cut, so that the bottom of one stood inside the 
bottom of this old one, leaving a space of half-an- 
inch between them. The cut part of the old jug that 
joined the side of the whole one was securely luted or 
soldered, to prevent .any access of air; both vessels, 
filled with water, were set on red embers without 
flame. Supposing, that in these railing days, you 
were one of these unfortunates that could not 
clean yourself in a morning without hot-water, and 
had to wait contentedly until this double - bottomed 
vessel contained liquid hot enough; would you not be 
worthy of being enshrined along with Patience on a 
monument? Even with the conduction of heat rising 
by the sides of the vessel, which could not be prevented, 
the single-bottomed vessel, in these circumstances, could 
be boiled several times before the other was well heated, 
and the balance between them only get restored when, 
after several trials, the lower bottom of the double- 
bottomed one got a hole burned in it. 1 think I men¬ 
tioned, some time ago, another simple evidence of the 
same fact, but will repeat it here, as these little matters 
often become of considerable importance. 1 was getting 
some zinc pans, for evaporation, placed on some round 
four-inch pipes, the bottom of the pans being semi¬ 
circular to clasp the pipe. The mechanic who made 
them was fixing them by placing a thin layer of red 
lead along the inner edges of the sides and ends of the 
pans, and then pressing them firmly down on the pipes. 
It struck me that thus there would be a cavity between 
the pipe and the pan, in proportion to the thickness of 
the red lead used in fixing them. The workman was 
well aware of the properties of enclosed air, but he 
could not think it could tell in such a minute affair as 
this. There is nothing, however, liko practical proof. 
Other pans had a slight coating of red lead all over the 
