Alberti, Leone Battista, Architecture, 1755

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            <p type="head">
              <s>CHAP. XII.</s>
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            <p type="head">
              <s>
                <emph type="italics"/>
              Of Coverings of ſtrait Lines; of the Beams and Rafters, and of the uniting
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              the Ribs.
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              </s>
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            <p type="main">
              <s>Of Coverings, ſome are to the open Air,
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              and ſome are within; ſome conſiſt of
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              ſtrait Lines, others of curve, and ſome of both:
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              We may add, not improperly, that ſome are
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              of Wood, and ſome of Stone. </s>
              <s>We will firſt,
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              according to our Cuſtom, mention one Obſer­
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              vation which relates in general to all Sorts of
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              Coverings; which is this: That all manner of
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              Roofs, or Coverings have their Ribs, Nerves,
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              Finiſhings, and Shells, or Cruſts, juſt the ſame
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              as the Wall: Which will appear from the
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              Conſideration of the Thing itſelf. </s>
              <s>To begin
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              with thoſe of Wood, and conſiſting of ſtrait
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              Lines; it is neceſſary for ſupporting the Cover
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              to lay very ſtrong Beams acroſs from one Wall
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              to the other; which, as we took Notice be­
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              fore, are Columns laid tranſverſe: Theſe
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              Beams therefore, are a Sort of Ribs; and if
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              it were not for the Expences, who would not
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              wiſh to have the whole Building conſiſt, if we
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              may uſe the Expreſſion, of nothing but Ribs
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              and ſolid Work; that is to ſay, of continued
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              Columns and Beams cloſe compacted? </s>
              <s>but we
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              here conſult Oeconomy, and ſuppoſe every
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              Thing to be ſuperfluous, that without Pre­
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              judice to the Strength of the Work, may be
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              poſſibly retrenched; and for this Reaſon, we
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              leave Spaces between the Beams. </s>
              <s>Between
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              theſe we lay the Croſs-beams, Rafters, and the
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              like; which may not at all improperly be
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              reckoned the Ligatures: To theſe we fit and
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              joyn Boards and Planks of greater Breadth,
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              which there is no Reaſon why we ſhould not
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              call theFiniſhing; and in the ſame Way of think­
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              ing, the Pavement and Tiling is the Outward
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              Shell, and the Ceiling, or Roof, which is over
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              our Head the Inward. </s>
              <s>If this be granted, let
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              us conſider whether there is any Thing ne­
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              ceſſary to be obſerved with Relation to any of
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              theſe Parts, that having duly examined it, we
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              may the more eaſily underſtand what belongs
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              to Coverings of Stone. </s>
              <s>We will ſpeak of them
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              therefore as briefly as poſſible: Firſt, taking
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              Notice of one Thing not foreign to our Pur­
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              poſe. </s>
              <s>There is a very vicious Practice among
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              our modern Architects; which is, that in
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              order to make their Ceilings, they leave great
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              Holes in the very Ribs of the Building to let
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              the Heads of the Beams into after the Wall is
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              finiſhed; which not only weakens the Struc­
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              ture, but alſo makes it more expoſed to Fire;
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              becauſe by theſe Holes the Flames find a
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              Paſſage from one Apartment to another. </s>
              <s>For
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              which Reaſon, I like the Method uſed among
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              the Ancients, of ſetting in the Wall ſtrong
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              Tables of Stone called Corbels, upon which
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              they laid the Heads of their Beams. </s>
              <s>If you
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              would bind the Wall, and the Beams together,
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              you have Braſs Cramps, and Braces, and
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              Catches or Notches in the Corbel itſelf, which
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              will ſerve for that Purpoſe. </s>
              <s>The Beams ought
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              to be perfectly ſound and clear; and eſpeci­
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              ally about the Middle of its Length it ought
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              to be free from the leaſt Defect, placing your
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              Ear at one End of it while the other is ſtruck,
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              if the Sound come to you dead, and flat, it is
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              a Sign of ſome private Infirmity. </s>
              <s>Beams that
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              have Knots in them are abſolutely to be re­
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              jected, eſpecially if there are many, or if they
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              are crouded together in a Cluſter. </s>
              <s>The Side
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              of the Timber that lies neareſt the Heart,
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              muſt be planed, and laid uppermoſt in the
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              Building; but the Part that is to lie under­
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              moſt, muſt be planed very ſuperficially, only
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              the Bark, nay, and of that hardly any, or as
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              little as poſſible. </s>
              <s>Which-ſoever Side has a
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              Defect that runs croſſways of the Beam, lay
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              uppermoſt; if there is a Crak longways, ne­
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              v̊er venture it of the Side, but lay it either
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              uppermoſt, or rather undermoſt. </s>
              <s>If you hap­
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              pen to have Occaſion to bore a Hole in it, or
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              any Opening, never meddle with the Middle
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              of its length, nor its lower Superficies. </s>
              <s>If, as in
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              Churches, the Beams are to be laid in Couples;
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              leave a Space of ſome Inches between them,
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              that they may have Room to exhale, and not
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              be ſpoyled by heating one another: And it
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              will not be amiſs to lay the two Beams of the
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              ſame Couple different Ways, that both their
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              Heads may not lie upon the ſame Pillow;
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              but where one has its Head, the other may
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              have its Foot: For by this Means the Strength
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              of the one's Foot will aſſiſt the Weakneſs
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              of the other's Head; and ſo
                <emph type="italics"/>
              vice verſa.
                <emph.end type="italics"/>
              </s>
              <s> The </s>
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