" -- -
DOM
276
DOM
the truncated segment of a sphere, considerably less than ahemisphere. The diameter of the dome internally is 142feet 8-| inches ; the circular opening at the top in the centre28 feet 6 inches in diameter ; the height from the top of theattic 70 feet 8 inches. The interior of the dome is orna-mented with five rows of square compartments, and as theseconverge towards the top, each row is considerably larger thanthat immediately above it. Each of the large squares con-tains four smaller ones sunk one within the other. It is sup-posed that these were decorated with plates of silver. Thebase of the dome externally consists of a large plinth with sixsmaller plinths or steps above it ; and in the curve of thedome a flight of steps is formed which leads to the openingat the top of the dome. From the drawings of Serlio , itappears that similar flights of steps were formed at intervalsall round the dome, but these are now covered with lead.The dome is constructed of bricks and rubble. The thick-ness at the base is about 17 feet ; at the top of the highest
step, 5 feet 1^ inches ; and at the top of the dome, 4 feet 7
inches. The circular wall which supports the dome is 20feet thick, but is divided by several large openings, and hasi discharging arches of brick. The dome of the Pantheon is[ incombustible, and is perhaps the cheapest as well as thej most durable and unconsumable roof which could have beenI erected over so large a building.
I The dome of the temple of Bacchus is also internallyi hemispherical, though without coffers. Externally it is now[ covered with a common roof, which may have been thej original form ; such a roof is also to be seen over the dome
! of the temple of Jupiter, in the palace of Diocletian , at
I Spolatro.
j The dome of one of the chambers of the Thermae of Catania j was 111 feet in diameter. In the Thenn® of Titus thereare two domes, each 84 feet in diameter ; and in the bathsof Constantine there was one of 76 feet. There were threedomes in the baths of Diocletian , of which two still remain ;one is 73 feet 6 inches in diameter, and the other 62 feet3 inches. Judging front those that remain, it would seemthat in the Therm® they were lighted from the top, in thesame manner as in the dome of the Pantheon . In the neigh-bourhood of Puzzuoli there is a circular edifice which has adome built of pumice-stone and volcanic tufa : its diameter isabout 96 feet. The temple of Minerva Medica, at Rome ,was on the plan, a polygonal dome of ten sides, without anyopening at the top. Domes were sometimes constructed oncorbels by the ancients. In one of the octagonal rooms ofthe enclosure round the baths of Caracalla the corbels whichsupported the dome still remain, and at Catania there is aspherical dome covering a square vestibule.
The dome of Santa Sophia, at Constantinople , built in thereign of Justinian, ranks next to the Pantheon in point ofantiquity, and is the most remarkable and the earliest con-structed after those of the Romans. Anthemius of Tralles ,and Isidorus of Miletus, were the architects. Anthemius hadpromised to raise a dome over this edifice, of such magnitudeas to eclipse the magnificence of the Roman Pantheon . Withthis view, he erected four pillars at the angles of a square, atabout the distance of 115 feet from each other, and nearly ofthe same altitude. The church was to be of the form of across, and vaulted with stone; he therefore threw archesover the pillars, and filled up the angular spaces between thearchivaults, till he had gradually shaped them into a completecircle, at the level of tiie extradoses of the arches. On thering thus formed, the dome was raised, being the first everbuilt on pendentives The pressure of the eastern andwestern arches was resisted by four walls almost solid, form-ing transepts, and running longitudinally, two from the north.
and two from the south sides of the pillars, to theof about 90 feet. The east and west arches were a ^upon by half-domes, resting on cylindrical walls, w j Slir e ofsupposed, would have been sufficient to resist the p re , j [e ctthe arches on the north and south ; but in this lard* th«was mistaken ; for the superstructure gave way tow ^ [fieeast, and, at the end of a few months, fell, taking wit t |, ehalf-dome on that side. After the death of Anthem*^ ’^jjosuperintendence of the building devolved on Isidor. ’ 0 ;dsstrengthened the eastern pillars, by filling up certai oe ileft by his predecessor ; but when the dome ' v 'J a9 gU ppor tupon them, the east end proved still too weak for ,C work <of So great a load, and again gave way, before the ellS t,
completed. In order to counteract this thrust on
the
linst
the
Isidorus now built strong pillared buttresses
eastern wall of a square cloister that ran round the a po
from which he threw flying buttresses over the v ’ces 3 ’
then raised the dome a third time, but with very li ttie ffe jgUb
for though every precaution was taken to lessen 1 and
by using pumice-stone and other light materials, fiia 1
reducing its thickness, the arches were so much frac , e g oH
he was under the necessity of filling up the large a - oD s , 111
the north and south sides, with arches of less dime
three stories. t j,at ^
We have mentioned these circumstances, to sho' e( j ; vt ete
architects of the age to which this building is re e ^ aU )tii4;’
not so well acquainted with the principles of dome pl . 0 baW
as those of more modern date : for the latter w° u p ve r tb®
have hooped or chained such a dome immediate 1 pe r
arches and pendentives, so as to confine its pressu j,, tj
.. .
the P
raeW
,la
of our countryman, Sir Christopher Wren , inSt. Paul's, at London . The present dome, howeve^ Jtr e *Sophia, was reconstructed by the nephew 0 , a ,.jns
on the square formed at the intersection of the a>
Greek cross ; the diameter being about
in
rbellingaP^ed
pe
dome 40 feet high, and is supported by corbeim's^.the angles of the square. These corbels are sur jj* er y. 'pa kind of cornice on which rests a circular S f* <i
lower
columns on ^ a row of windows
lantern on which i« n0r ’ and tile t0 P is surmounted :‘ ,|U
Isidorus, was Ho 1 Tbe of »
earthquake a few years afti ^ W8S pM - ly
it, the nephew of Lvi t r lts construction. In r f ,at Bhodei and t 1 , d , 01 ' US used a ^ry light white brick,
The dome of St°M. ,g t ter tban tlle common bn< f [he ,W r
973, and that of *'t at Venice, erected about t j,e
eleventh centurv le cathedral at Pisa, built ea! ' 7.i, e pr e ’ceding jn lp fi, aie , botb u Pon the same plan with ( I1 tl>
centufy, has five^dn° f , Saint Mark > budt in
domes ; the central dome being muC - of
’ — -vi.in f
A K
enchisedwithin- ;
tau c - e i
’four P**
than the others. Each dome issemi-cylindrical vaulting, together formingangles of this square are four corbels, \vln c 1 - nll s, tb e ‘TwoHcircular base of each dome. " ‘~^ ’‘ '
I r t! ‘ 0
tec t, repaired t I In lS23 > Sansoviuus, t]l ®pyc
T °und it to Drpv „ s dome > and placed a circleJ>
taken with one of“tl US fldUn S- A similar i“
1735, with the som sma ^ er domes by Andrew
The dome of re sult. .;„us c ° r
st i’uction. The ni. le at Ravenna, is of very cm eff aln (
octagon, supported 1” ° - tbe lower part is that of ® f 0 o> e ’
between tifese ano-l P e>ght piers ilt tlie a,lgieS< .ffin‘ 0 C "lstories. Tim lm‘ b ^ £,re seven hill niches divide 3
with colon, T, er pan of these niches is open, and ^
S ‘ Ii,e remaining side of the dome
l