DOI Page / Citation link:
https://doi.org/10.11588/diglit.62828#0175
ellipfis between o and / into as many equal parts as it is required
to have ribs in one quarter of the dome, as at o a b i j k I, tending
to the center b.
From thefe center lines draw parallel lines on each tide,
which fhall determine the thicknefs of the ribs, and at the fame
time fhow how broad each rib will be required, in order to give
it its proper twill fo as to fuit the ellipfis; for here it mult be
obferved, that every rib, excepting the one that is upon each
femidiameter, mult have a winding form, both iniide and
outfide, in proportion to the length of the oval with its
breadth.
Determine, next, how much the dome is to rife from the
teller, which, in this example, I confider to be equal to half
the Ihort diameter; and therefore the arch of the rib B is a
quadrant of a circle, drawn from the center b. This arch will
ferve for two ribs, that is, B and its oppolite. Likewife, from
the arch B, we determine the outline of every other rib thus:
divide the femidiameter a b into five and an half equal parts,
and raife perpendiculars till they touch the arch B. Divide the
plan of the rib a b at No. 2 into the fame number of equal
parts, and raife perpendiculars at pleafure; to which perpendi-
culars transfer the feveral lengths of thofe at No. 1 to the cor-
refponding ones at No. 2, as acdefg-, by which the rib A
will be formed. The ribs for b ij and k are formed in the
fame
to have ribs in one quarter of the dome, as at o a b i j k I, tending
to the center b.
From thefe center lines draw parallel lines on each tide,
which fhall determine the thicknefs of the ribs, and at the fame
time fhow how broad each rib will be required, in order to give
it its proper twill fo as to fuit the ellipfis; for here it mult be
obferved, that every rib, excepting the one that is upon each
femidiameter, mult have a winding form, both iniide and
outfide, in proportion to the length of the oval with its
breadth.
Determine, next, how much the dome is to rife from the
teller, which, in this example, I confider to be equal to half
the Ihort diameter; and therefore the arch of the rib B is a
quadrant of a circle, drawn from the center b. This arch will
ferve for two ribs, that is, B and its oppolite. Likewife, from
the arch B, we determine the outline of every other rib thus:
divide the femidiameter a b into five and an half equal parts,
and raife perpendiculars till they touch the arch B. Divide the
plan of the rib a b at No. 2 into the fame number of equal
parts, and raife perpendiculars at pleafure; to which perpendi-
culars transfer the feveral lengths of thofe at No. 1 to the cor-
refponding ones at No. 2, as acdefg-, by which the rib A
will be formed. The ribs for b ij and k are formed in the
fame