1which are turned upon Centres, when they are
cloſed with their Key-ſtones, it will be proper
immediately to eaſe the Props a little, that
thoſe Centres reſt upon; not only to prevent
the Stones freſh laid from floating in the Beds
of Mortar they are ſet in, but that the whole
Vault may ſink and cloſe by its own Weight
epually, into its right Seat: Otherwiſe in drying,
the Work would not compact itſelf as it ought,
but would be apt to leave Cracks when it came
afterwards to ſettle. And therefore you muſt
not quite take away the Centre immediately,
but let it down eaſily Day after Day, by little
and little, for Fear, if you ſhould take it away
too ſoon, the Building ſhould never duly cement.
But after a certain Number of Days, according
to the Greatneſs of the Work, eaſeit a little, and
ſo go on gradually, till the Wedges all compact
themſelves in their Places, and are perfectly
ſettled. The beſt Way of letting down the
Frame is this: When you place your Centre
upon the Pilaſters, or whatever elſe it is to
reſt upon, put under each of its Feet two
Wedges of Wood; aud when afterwards you
want to let it down, you may with a Ham
mer ſafely drive out theſe Wedges by little
and little, as you ſhall judge proper.
cloſed with their Key-ſtones, it will be proper
immediately to eaſe the Props a little, that
thoſe Centres reſt upon; not only to prevent
the Stones freſh laid from floating in the Beds
of Mortar they are ſet in, but that the whole
Vault may ſink and cloſe by its own Weight
epually, into its right Seat: Otherwiſe in drying,
the Work would not compact itſelf as it ought,
but would be apt to leave Cracks when it came
afterwards to ſettle. And therefore you muſt
not quite take away the Centre immediately,
but let it down eaſily Day after Day, by little
and little, for Fear, if you ſhould take it away
too ſoon, the Building ſhould never duly cement.
But after a certain Number of Days, according
to the Greatneſs of the Work, eaſeit a little, and
ſo go on gradually, till the Wedges all compact
themſelves in their Places, and are perfectly
ſettled. The beſt Way of letting down the
Frame is this: When you place your Centre
upon the Pilaſters, or whatever elſe it is to
reſt upon, put under each of its Feet two
Wedges of Wood; aud when afterwards you
want to let it down, you may with a Ham
mer ſafely drive out theſe Wedges by little
and little, as you ſhall judge proper.
LASTLY, it is my Opinion, that the Centres
ought not to be taken away till after Winter,
as well for other Reaſons, as becauſe the
Waſhing of the Rains may weaken and de
moliſh the whole Structure; though elſe we
cannot do greater Service to a Vault than to
give it Water enough, and to let it be
thoroughly ſoak'd, that it may never feel Thirſt.
But of this Subject we have ſaid enough.
ought not to be taken away till after Winter,
as well for other Reaſons, as becauſe the
Waſhing of the Rains may weaken and de
moliſh the whole Structure; though elſe we
cannot do greater Service to a Vault than to
give it Water enough, and to let it be
thoroughly ſoak'd, that it may never feel Thirſt.
But of this Subject we have ſaid enough.
CHAP. XV.
Of the Shell of the Covering, and its Uſefulneſs; the different Sorts and
Shapes of Tiles, and what to make them of.
Shapes of Tiles, and what to make them of.
I now come to cover the Roof. And cer
tainly, if we weigh the Matter duly, there
is no Convenience in the whole Building
greater than the having Shelter from the burn
ing Sun, and the inclement Seaſons; and this
is a Benefit which you owe the Continuance
of, not to the Wall, nor to Area, nor any of
theſe; but principally to the outward Shell of
the Roof; which all the Art and Induſtry of
Man, though they have tried all Means, has
not yet been able to make ſo ſtrong and im
penetrable againſt the Weather as might be
wiſh'd: Nor do I think, it will be an eaſy
Matter to do it; for where, not only Rains,
but Extremes of Heat and Cold, and above
all, bluſtering Storms of Wind, are continu
ally aſſaulting the ſame Place; what Mate
rials are ſtrong enough to reſiſt ſuch unwearied
and powerful Adverſaries? Hence it happens,
that ſome Coverings preſently rot, others open,
others oppreſs the Wall, ſome crack, or break,
others are waſhed away; inſomuch, that even
Metals, which are ſo hardy againſt the Wea
ther, in other Places, are not here able to hold
out againſt ſuch frequent Aſſaults. But Men
not deſpiſing ſuch Materials as Nature furniſh
ed them with in their reſpective Countries,
have provided againſt theſe Inconveniences as
well as they were able; and hence aroſe various
Methods of Covering in a Building. Vitruvi
us tells us, that the Pyrgenſes covered their
Houſes with Reeds, and the People of Mar
ſeilles with Clay kneaded, and mixed with
Straw. The Chelonophagi, near the Garaman
tes, Pliny tells us, cover'd theirs with the
Shells of Tortoiſes. The greateſt Part of Ger
many uſe Shingles. In Flanders and Picardy,
they cut a white Sort of Stone which they
have (which Saws eaſier than Wood itſelf) in
to their Scantlings, which they uſe inſtead of
Tiles. The Genoueze, and Florentines uſe thin
Pieces of a ſcaly Sort of Stone. Others have
tried the Pargets, which we ſhall ſpeak of by
and by. But after having made Experiment of
every Thing, the Wit and Invention of Man
has found out nothing yet more convenient
than Tiles of baked Clay. For all Sorts of
Parget grow rugged in Froſts, and ſo crack and
break: Lead is melted by the Sun's Heat:
Braſs, if laid in thick Plates, is very coſtly;
and if it is thin, it is apt to warp, and to be
eaten and conſumed with Ruſt.
tainly, if we weigh the Matter duly, there
is no Convenience in the whole Building
greater than the having Shelter from the burn
ing Sun, and the inclement Seaſons; and this
is a Benefit which you owe the Continuance
of, not to the Wall, nor to Area, nor any of
theſe; but principally to the outward Shell of
the Roof; which all the Art and Induſtry of
Man, though they have tried all Means, has
not yet been able to make ſo ſtrong and im
penetrable againſt the Weather as might be
wiſh'd: Nor do I think, it will be an eaſy
Matter to do it; for where, not only Rains,
but Extremes of Heat and Cold, and above
all, bluſtering Storms of Wind, are continu
ally aſſaulting the ſame Place; what Mate
rials are ſtrong enough to reſiſt ſuch unwearied
and powerful Adverſaries? Hence it happens,
that ſome Coverings preſently rot, others open,
others oppreſs the Wall, ſome crack, or break,
others are waſhed away; inſomuch, that even
Metals, which are ſo hardy againſt the Wea
ther, in other Places, are not here able to hold
out againſt ſuch frequent Aſſaults. But Men
not deſpiſing ſuch Materials as Nature furniſh
ed them with in their reſpective Countries,
have provided againſt theſe Inconveniences as
well as they were able; and hence aroſe various
Methods of Covering in a Building. Vitruvi
us tells us, that the Pyrgenſes covered their
Houſes with Reeds, and the People of Mar
ſeilles with Clay kneaded, and mixed with
Straw. The Chelonophagi, near the Garaman
tes, Pliny tells us, cover'd theirs with the
Shells of Tortoiſes. The greateſt Part of Ger
many uſe Shingles. In Flanders and Picardy,
they cut a white Sort of Stone which they
have (which Saws eaſier than Wood itſelf) in
to their Scantlings, which they uſe inſtead of
Tiles. The Genoueze, and Florentines uſe thin
Pieces of a ſcaly Sort of Stone. Others have
tried the Pargets, which we ſhall ſpeak of by
and by. But after having made Experiment of
every Thing, the Wit and Invention of Man
has found out nothing yet more convenient
than Tiles of baked Clay. For all Sorts of
Parget grow rugged in Froſts, and ſo crack and
break: Lead is melted by the Sun's Heat:
Braſs, if laid in thick Plates, is very coſtly;
and if it is thin, it is apt to warp, and to be
eaten and conſumed with Ruſt.