1849.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



11 



In alluiliriE; to the cupolas previously erected, the chevalier pays 

 a just tribute to the g:enius of our illustrious ^rreii, and recog- 

 nises St. Paul's "as the only existing dome presenting- an irre- 

 proachable solidity." He, therefore, adopted the principle of Sir 

 Christopher, carrying it out in a combination of wrought and cast 

 iron, and hollow pots. 



The walls of the drum of the dome are carried up in solid con- 

 struction of brick, with tiers of stone bond, and ai'e above 8 feet 

 thick. On the level of the top of the cornice of the circular 

 colonnade, which girds the drum, there is a series of twenty-four 

 cast-iron ribs A, the feet of which rest on a cast-iron plate B, 7 feet 

 wide, which runs quite round the circumference. The lowest 

 division of each rib rises to a height of about 23 feet ; in its 

 narrowest part is 3 ft. 4 in. wide, in its broadest 5 feet, with upper 

 and lower ril)s, and the central part lightened by large apertures. 

 At their head all the ribs are attached to a horizontal plate or 

 curb, C, () ft. 3 in. wide, which follows the periphery of the dome. 

 At this height the rib is divided into two «, «', the one ]>art a about 

 2 ft. 6 in. dee]), following the sweep of the inner dome for a height 

 of 20 feet; at its summit bolted to a cast-iron perforated cylinder 

 D, 21 feet in diameter, and 7 feet high: this forms the central 

 aperture at the summit of the inner dome. The other part «', 

 follows the line of an intermediate cone, with a catenary outline, 

 and similar to the one in our St. Paul's: it is also 21 feet long, 

 and 2 ft. 6 in. deep, and perforated to render it lighter. At this 

 height the heads of the ribs are again secured to another horizon- 

 tal plate or curb E, which forms a complete circle, and is 3 feet 

 wide; and this curb and the ribs are tied to the cylindrical open- 

 ing of the inner dome, already mentioned, by radiating beams, e, 

 2 ft. 3 in. deep. The conical ribs have then another length of 

 21 feet, rt", and their heads are again connected by another hori- 

 zontal plate, F, from which spring the circular ribs, a'", about 

 16 feet long, forming a dome to the intermediate cone, and their 

 heads also bolted to a cylinder G,8 ft.G in. in diameter, and 18 inches 

 high. But the upper portion of the ribs diverge at top, so as to 

 form a base for the octagonal cupidino, H, which consists of a 

 series of cast-iron stoi-y-posts, ribs, and bracketings, inclusive of 

 the dome of the cupolino, with its bail and cross at the apex, which 

 last are of brass gilt. The filling-in between the ribs consists of 

 pots, the surfaces of which were subsequently rendered with 

 plaster, and painted with sacred subjects. Tlie sphere of the 

 outermost or third dome, J, consists of a series of wrought-iron 

 T ribs tied to the conical dome by rods, y. The external face of 

 this outer dome is divided by twenty-four bold ribs, and is covered 

 with bronze, gilt in three thicknesses of leaves of ducat gold. 

 The three principal gilders of St. Petersburg were charged with the 

 inspection of the execution of this portion of the work, and rejected 

 every leaf that had the slightest spot or blemish. 



The whole entalilature and flat, and the balustrade over the peri- 

 style of the drum of the cupola, likewise consist of cast and wrought 

 iron framing, faced with plates of co]>per, to form the profiles and 

 mouldings. The twenty-four pedestals of this balustrade carry 

 winged angels of bronze, above 9 feet high, each of a single casting. 



The quantity of metal employed in the dome is as follows: — 



Ducat gold . . . . . . 247 lb. 



Copper .. .. Wl^ tons. 



Brass .. .. ,T_'|J tons. 



Wrought-iron .. .. wi\\ tons. 



Cast-iron .. .. loiiH tons. 



Total .. liwtij tons 3471b. 



The foresight of the architect has provided the following pre- 

 cautions against lightning,— much the more liable, as the summit of 

 each dome is in metal: at the top of the crosses of the hell 

 towers and of the cupolino of the central dome are rods of platina, 

 terminating in a point: each dome at its springing has isolated iron 

 conductors, which go down to the roofs; and in the direction of 

 the cast-iron rain-water pipes are continued in the interior of the 

 walls down to wells in the basement, the overflow of which dis- 

 charges into the town sewers. 



In justification of the system here employed let the architect 

 speak for himself:— "We think," says De Montferrand, "the 

 mode we have adopted superior to that of any other cupola. For 

 what can be more absurd than those vaultings raised 250 or 300 

 feet in the air— whose frightful weight, unceasingly in action, 

 tends to disunite the points of support which uphold 'them. Our 

 new system offers a stable combination, which allows of no dis- 

 union—which has no thrust, and which reduces to a tenth the 

 weight of any previous combination. In our plan, the iron and 

 bronze entablature of the peristyle of the drum is not a mere 

 architectural embellishment: it is a solid girdle, whicli embraces 

 firmly the dome, so as to give it a great stability; and can the 



superiority of this system be contested, when it is considered, that 

 here is employed the material which can alone, with prudent care, 

 brave the effects of a rigorous climate.^" 



The arches and vaults of the na\e and transepts and the soffits 

 of the porticoes are carried out in like manner by means of cast- 

 iron girders, to which are attached the marble facings and decora- 

 tive embellisliments. 



The rooting is wholly of iron, covered with copper. There are 

 thirty-four small columns of cast-iron, resting on the walls and 

 vaultings of the ceiling. These are tied together by a series of 

 invei-ted ([ueen trusses of wrought and cast-iron mixed, about 

 6 feet apart, with wrought-iron lathing to receive the copper. 

 The whole presents a very light effect, and is very simple in its 

 combination; and although the roof rises about 9 feet above the 

 level of the attic outside, yet it is not seen unless by those at a 

 very great distance from the building. 



In determining the thickness of the drum of the cupola, M. de 

 Montferrand has adopted the principle laid down by Fontana, of 

 making the thickness of this cylindrical wall equal one-tenth of 

 the internal diameter; although Rondelet and others allow a 

 much less thickness. Notwithstanding, a substantial base for this 

 great thickness of wall and the projecting architectural embel- 

 lishments of tlie dome, is afforded by the pendentives, which rise 

 from the four great piers of the dome, and form the circle for the 

 cylinder of the drum. 



The raising of the monolithic shafts of the twenty-four columns 

 of the exterior peristyle of the dome, — each of which weighed 

 near 66 tons, — to the height of ISO feet, was an operation re<|uir- 

 ing considerable skill. Each shaft was surrounded by a stout 

 casing, to which were attached strong cables. It was then placed 

 on an immense truck, calculated for the size of the vast block, and 

 drawn by capstans upon an easy incline to a platform, which was 

 on a level with the tops of the columns of the interior order, 

 42 feet high. Upon this platform was a moveable incline, 92 feet 

 high, but with a very sharp rise, and up this the monolitli was 

 again drawn by capstans. At the summit was a large platform, 

 180 feet square, upon which was a nmveable wooden framework, 

 answering the purpose of a crane, with blocks and falls. There 

 were twelve capstans around this framework. The monolith being- 

 dragged up the incline, reached the summit, and, by its own 

 weight tilting over, reached the framework; it was then by it 

 raised to a vertical position, and gradually lowered on a granite 

 die prepared to receive it, and wliich was cased with a bronze base. 



As soon as one monolith was in its place, the moveable incline 

 and the mo\eahle platform and frame were all wheeled round, 

 ready to raise the next column; and so on the operation was re- 

 peated until the whole series were securely fixed in their respecv- 

 tive places. It only required two hours to" raise one of the shafts 

 from the platform on a level with tlie capitals of the inner order, 

 and to fix it on its base. Three hundred men performed this 

 operation: the most perfect order and silence were maintained 

 throughout, and the different movements directed by the sound of 

 a bell. A silver rouble was placed on the base of each column, in 

 a hole sunk for the purpose. 



Tlie first column was raised on the 17th of November, 1837, 

 just eleven years ago from this period; nor was the operation com- 

 menced without prayers to Almighty tiod to bless the undertaking 

 with success. In two months the twenty-four columns were com- 

 pletely fi.xed, and, be it remembered, in the very depth of a 

 Uussian winter. 



The skeleton of the entablature of the peristyle of the dome is 

 of cast and wrought-iron, resting on the columns, and affixed to 

 them by wrought-irou pins, which are let a considerable depth into 

 the shafts; and the framework is also let into the cylindrical wall 

 of the dome, securely affixed to three templates. The cornice, 

 with its modillions and mouldings, rest on cast-iron corbels; the 

 caissons and rosettes of the inner soffit also rest on cast-iron 

 girders. The balustrading above is similarly framed, and the 

 pedestals support bronze figures of angels, already mentioned, 

 liolding their attributes, each 9 feet high, and of only a single 

 casting, weighing i;^ tons. The balusters are also of bronze. 



I may perhaps be permitted to observe that the bronze bases, 

 capitals, figures, and other decorative details of this material on 

 the outside are neither gilt nor painted; consequentlv, the dark 

 tone ot these parts has a heavy appearance, and ill accords with 

 their purpose and the stonework of the outer facing. 



In the presence of such an assembly, so competent to judge of 

 the merits of this important monument of our art, it would ill 

 become me to offer any remarks, other than those which I have 

 already made, upon the most striking points in regard to taste and 

 skill, which distinguish this production of our honorary member. 



3* 



