_HOW PAUL IS LED TO RECOGNIZE CERTAIN DISTINCTIONS BETWEEN ETHICS AND
ARCHITECTURE._
When, in the evening, Paul’s report of the lesson was read in the
family circle, M. de Gandelau interrupted the reading at this phrase
incorrectly given, “Good is only the absence of evil.”
“Oh, oh!” said his father; “Charity is something more than the absence
of evil. If you give nothing to the poor man who asks bread of you; if,
being able to swim, you do not try to save a drowning man, you do not
do evil, but certainly you do not do good.”
“That is not exactly what I said to Paul,” replied Eugène, smiling.
“Respecting defects discovered in building, I said, ‘I believe that
the good is the absence of the bad;’ that is to say, in building
operations, and perhaps in many other matters belonging to the purely
material order of things, to avoid what is bad is to do well, but not
to do good. I must, however, admit that I did not sufficiently develop
my thought.
“Two things are needed to make a good builder: clear-sighted
intelligence—which depends on our individual psychical nature—and the
experience we acquire.
“Observation and experience thence resulting enable us to recognize
what is defective and to avoid it; but if, notwithstanding the
advantage thence derived, we are not endowed by nature with
clear-sighted intelligence, experience, though enabling us to avoid
the bad, does not of itself suffice for the discovery of the good.
“Moreover, though in morals the good is absolute and independent of
circumstances, it is not the same with building. What is good here is
bad elsewhere, on account of climate, habits, nature of materials,
and the way in which they are affected by local circumstances.
While, for instance, it is desirable to cover a roof with slates in
a temperate and humid climate, this kind of roofing is objectionable
in a warm, dry, and windy climate. Wooden buildings will be excellent
in one situation and unsuitable in others. While it is desirable
to admit the light by wide openings and to glaze large surfaces in
northern climates, because the sun’s glare is subdued, this would be
objectionable in southern countries, where the light is intense, and
where it is necessary to procure shelter from the heat. A code of
morals is possible, but we cannot establish absolute rules in building;
experience, reasoning, and reflection must therefore always be summoned
to our aid when we attempt to build. Very often young architects have
asked me what treatise on building I should recommend as the best.
There is none, I tell them; because a treatise cannot anticipate all
contingencies,—all the special circumstances that present themselves
in the experience of an architect. A _treatise_ lays down rules; but
ninety-nine times out of a hundred you have to encounter the exception
and cannot rely upon the rule. A treatise on building is useful in
habituating the mind to devise plans and have them put into execution
according to certain methods; it gives you the means of solving the
problems proposed; but it does not actually solve them, or at least
only solves one in a thousand. It is then for intelligence to supply in
the thousand cases presented what the rule cannot provide for.”
LESSON THE THIRD.
“Yesterday,” said Eugène to Paul, when the latter came into his room,
“we visited the cellars and the ground floor; now we shall take a walk
among the garrets of the _château_. But first I must show you what
is meant by a roof _truss_. The simplest truss (Fig. 13) is composed
of four pieces of wood: two principal rafters, a tie-beam, and a
king-post. The two inclined pieces A are the blades; the horizontal
piece B is the tie-beam, and the vertical piece C the king-post. The
upper ends of the blades meet in the king-post, as I show you in
the detail D,—namely, by the means of two tenons E, which fit into
two mortises F, and a shoulder G, which make the whole pressure of
the timber bear into the notch I. The lower ends of the blades are
similarly connected at the two extremities of the tie-beam, as this
other detail H shows us. The king-post is also connected by a tenon,
in the centre of the tie-beam, but loosely, and without bearing upon
this tie-beam. When the tenons are let into the mortises, pegs of wood
are driven into the holes marked to fasten the whole well. The more
pressure there is on the top, M, the more the two blades tend to spread
at the foot; but these, being fixed at the two ends of the tie-beam,
tighten the latter like the string of a bow. The more this tie-beam is
strained, therefore, the less it is inclined to bend, and the object
of the king-post is only to suspend it by its centre, and to connect
the heads of the blades. But between M and N these rafters may bend
under the weight of the roof covering; two struts, O P, therefore are
added, which arrest this bending by bringing the pressure to bear on
the king-post, so that the latter is in its turn strained between M and
P. As wood will not stretch, the point P is fixed, and the two points O
likewise.
[Illustration: FIG. 13.]
“Now that you know what is the simplest roof-truss, let us go up into
the roofs.”
These roofs were old, and had been repaired and strengthened many
times, and formed a complication of timbers difficult enough to
understand.
“Formerly,” said Eugène, “that is, more than a century ago, they used
to make roofs such as you see here: every rafter was framed, that
is, each of the rafters composed a truss, except the tie-beam, which
was introduced only at intervals. Then wood was in plenty, and they
scarcely thought of economising it. At present it is less abundant,
and there is a difficulty in procuring a considerable number of pieces
of large dimensions. The noble forests that covered the soil of France
have been foolishly wasted, and long timbers of heart of oak are rare.
It has therefore been necessary to economise them. The expedient has
been adopted of placing strong trusses at a distance of about 12 feet
from each other. On these trusses have been placed _purlins_, which
are the horizontal pieces you see on this side; and on these purlins
longer or shorter rafters have been placed to receive the lathing for
the tiles, or the battens for the slates. But all timber roofing should
be fixed upon sleepers, which are those horizontal pieces resting on
the top of the walls, which bind and isolate the tie-beams from the
masonry; for it is to be observed that timber is preserved for an
indefinite time in the free dry air, but soon decays in contact with a
moist body, such as stone is. Look here at this piece of wood, almost
buried in the masonry; it is nearly reduced to touchwood, while the
blade above, which is in the free dry air, is as free from rot as if it
were new.
“Formerly upper floors were made by putting joists resting on beams
and the walls. These joists and beams remained visible, as you may see
still in the kitchen and the large hall on the ground floor, which
serves as a store-room. The air therefore could circulate round these
timbers, and they might last for centuries. But it was considered
that thus exposed they were not pleasant to look at—that they were
not clean, and allowed spiders to spin their webs in the interspaces.
Laths were therefore nailed under these joists, and this lathwork
plastered so as to form what we call a ceiling. Timbers thus inclosed
and deprived of air, ‘heated’ (as carpenters call it), that is, they
fermented and soon began to decay. In fact, floorings with exposed
joists which had resisted the action of time for centuries decayed
and broke down in a short time after being inclosed. I may add that
formerly, before using timber in building, they took the precaution of
leaving it exposed for some years to the action of the sun and rain.
They even kept it for some time in water, to free it from the sap (for
sap is the ferment which makes wood rot). When the timber, after having
been barked and roughly squared, had remained in the open air for five
or six years, it was used. But now-a-days we are in a hurry, and make
use of timber that has not been cut more than a year. It is not dry,
it retains its sap, and if it is then enclosed it ferments rapidly, so
that in a few years the largest beams are completely rotten. Prudent
architects therefore hesitate to use wood for floors. Yet its use—even
if only partially dried—would not entail serious inconvenience if it
was not covered with plaster. The worst that could happen would be the
occurrence of cracks and shrinkings. It would dry when in use, as it
would have dried in the open air.
“There is no great disadvantage, then, in employing wood newly cut for
roof-timbers, which are generally left exposed. They dry where they
are. They warp, but do not perish of dry-rot.
“As we shall not be able to find wood absolutely dry for your sister’s
house, we shall leave the floor-joists visible, and endeavour by simple
and economical means to render them not unsightly.
“But you ought to be well acquainted with the qualities of timber.
I will not tell you that nature has caused these large vegetable
growths which we employ to grow for our pleasure or use. Nature is, I
think, very little concerned as to whether the oak or the fir would
serve any of our purposes; and if human intelligence has been able
to take advantage of these materials that spring up before us, it is
after having recognized and verified their properties by experience.
Unfortunately, it would seem as if the results of this experience did
not tend to increase; and judging from the way in which building-timber
is most frequently employed, we might be led to suppose that we are
less informed than were our predecessors, or that we have lost that
habit of observation with which they were familiar.
“Wood, being composed of fibres more or less lax or compact, possesses
a considerable power of resistance to a pressure exerted along these
fibres, but is easily bent or crushed under a pressure exerted across
these same fibres. Thus a log of wood 4 inches in diameter and a yard
or so long, placed on end, will support, without being crushed or
contorted, a pressure of 40,000 lbs.; whereas this weight will break
or crush it if placed horizontally, as you would crush a reed under
your foot. Take a thoroughly sound bit of straw, 4 inches long, and
place your finger on one end of it, holding the straw vertically on a
table; you will have to press pretty strongly on it to bend it, while
the least pressure on the same straw placed horizontally will flatten
it. The straw is a tube. A tree consists of a series of tubes, some
enveloping others. The more numerous, close and fine these tubes are,
the more does the trunk resist pressure, either in the direction of its
length or its thickness. But this shows us that to enable the wood to
retain its power of resistance we must employ it as nature gives it to
us; and in fact this was done formerly. Each piece of timber was cut
from a tree of larger or smaller size, as the case required, but they
did not split the tree lengthwise to get several pieces of timber; for
the heart being harder and more compact than the sap-wood (which is
the spongy envelope beneath the bark), and the concentric layers of
wood being the closer and tougher in proportion to their nearness to
the bark, if you split a tree in two lengthwise one of its faces is
much more resisting than the other, the equilibrium is disturbed, and
flexure is easily produced under a weight. The outer layers, being the
more recent, are more spongy and lax in texture than the older layers
that are near the heart; consequently the process of drying makes these
outer layers shrink more than the inner: hence curvature. Let A (Fig.
14) be a split piece of wood; the layers B are harder and more compact
than those marked C, which contain more moisture and whose fibres are
softer. In drying, therefore, this piece of wood will present a hollow
bend on the outer side, as I show at D. If the wood is left entire, as
at E, the effects of drying will neutralize each other, and the piece
will remain straight.
[Illustration: FIG. 14.]
“Look at this old roof, whose rafters are framed (Fig. 15): the wall
plates, A, are cut from small trunks, the heart being in the centre.
It is the same with the rafters B, the tie-beams C, the collars D,
the king-posts E, the foot-pieces F, and the foot-posts G; all these
pieces, therefore, have preserved their rigidity, and none of them has
been bent, because they were used dry and were unsplit trunks. Observe,
on the contrary, this purlin, H, placed on this truss, I, of recent
date; it is bent not so much on account of the weight of the rafters
it supports as because it is split and the carpenter has unadvisedly
turned the heart on the inside. If he had done the contrary,—if the
heart had been placed next to the rafters,—this purlin would probably
not have bent, perhaps have even become more rigid—that is to say,
it would be convex on the outer side. Carpenters, however, are but
men, and they do not care to give themselves trouble when they think
they can avoid it. The man that put this purlin here found it more
convenient to place it on its sawn side than to turn it the other way
with the flat under the rafters.
[Illustration: FIG. 15.]
“Considering this quality of wood, and of oak especially (whose
internal fibres are harder and closer than the outer layers), when we
have to place a piece of wood horizontally on two points of support or
posts, and wish to give it all the strength possible to bear a weight
acting on its centre, we saw it in two lengthwise, and turning the flat
faces outside, bolt these two pieces together, as shown here (Fig.
16). Then as the heart-wood is outside, and the two pieces tend to
become bent, forming two convex surfaces, as you see at A (Fig. 17), if
they are firmly held by bolts furnished with good heads and nuts, they
must remain straight; the tendency to curvature in the one neutralizing
that in the other, these two opposing forces tend to make the piece
more rigid, so that, if you take a piece of timber that is slightly
bent naturally and then place these two pieces with their hollow
downwards,—that is, after having placed one upon the other, putting the
tail of one against the head of the other,—you will have given this
piece of wood all the resisting power of which it is capable.
[Illustration: FIG. 16.]
[Illustration: FIG. 17.]
“It is in this way that _clips_ and all coupled pieces should be
placed. Here, for example (Fig. 18), you see a pair of clips where the
sawn faces have been turned outside to replace a decayed tie-beam.
We call clips those pieces of wood which, in pairs, usually clench
two or more parts of a framing. These clips, A, hold fast by means of
notchings, the blades B, the king-post C, and the two struts D. Iron
bolts with screw-nuts tightly hold the notchings of the clips, like
a pair of jaws, against the timbers which have to be kept in their
place. But this is enough for to-day, and you will have plenty to do to
make a fair transcript of this lesson in carpentry between now and this
evening.”
[Illustration: FIG. 18.]