This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
165. Plate XXX shows an Ionic portico or porch attached to an edifice circular in form. The circular hall is six entablatures twenty parts in diameter, and the thickness of the wall is fifty parts. The perimeter of the hall is divided by pilasters of a smaller order than that on the exterior into twelve bays, as shown in the plan in Fig. 29. The difference in size is due to the pedestal, ninety parts in height, on which the pilasters are placed.
The scale for this interior order is obtained by dividing the total height of the pilaster and its entablature into five parts (each part representing one entablature of the interior order).
166. This circular hall is covered by a spherical cupola or dome, divided into caissons or coffers, the drawing of which constitutes the most interesting part of this exercise; it will therefore be explained as clearly as possible. It is illustrated on Plate XXX.
167. The projection of the interior pilasters being ten parts (at the scale of that order) from the face of the wall, the interior diameter of the springing of the cupola is six entablatures. Draw a half plan of the cupola, dividing its circumference into twelve equal parts and then draw the radii; lay off on each one of these radii, outside the circumference, the profile of a rib and the two coffers one on each side of the rib, each eighteen parts wide, and the two coffers seven parts each and three parts in depth. Next draw in on the plan two semi-circles, one of three entablatures and three parts radius, the other of three entablatures six parts radius. Having thus established the whole profile of the springing of the cupola, draw from each division a radius to the center; then show above this plan, centering on the same axis, the section of the cupola, whose center will be found forty parts below the first horizontal course. This height of forty parts forms a conge with an astragal above the cornice. The cupola is divided into five rows of caissons whose height is relative to their width. Notice that the first band above the astragal is fifteen wide; draw the vertical line from the point A (section) to the point A (plan); draw the quarter circle A which intersects at E and F the lines of the rib. Take from the plan the width EF and lay it off from A to B along the curve on the section, thus obtaining the height of the first row of caissons. From the point B (section) draw a vertical to the (plan) and draw the quarter circle through B' in plan intersecting the radii at G and H. This distance (G H) laid off along the curve from B to C shows the width of the second horizontal band. Now project the point C (section) to C (plan) and draw the quarter circle C' on which CD' will give the height of the second row of caissons which will be laid off from C to D along the curve in the section. Continue this operation up to the fifth row of caissons. As to the widths of the coffers, they are found on the plan of each row of caissons and consequently diminish gradually with them. The profile of the caissons is formed in the section in this way and their location is found in plan. From
PLATE XXXIII. (A reproduction at small size of Portfolio Plate XXXIII.)
PLATE XXXIV. (A reproduction at small size of Portfolio Plate XXXIV.)
WENDELL PHILLIPS HIGH SCHOOL, CHICAGO, ILL.
Wm. B. Mundie, Architect. Built in 1904. Cost, $300,000. Note the Use of Ionic Pilasters each angle of the profile of the caisson draw a horizontal line through the section; this will give the horizontal lines on which all the points of intersection will be found in projecting the verticals from the corresponding points in the plan. Thus, from the point I (plan) which is found on the upper line of the topmost row of caissons, draw a vertical up to the point I (section) which is on the corresponding line in the section; from the point J (plan), which is found on the lower line of the same row of caissons, draw a vertical to the point J (section). Thus the circle I (plan) is represented in the section by the horizontal line I; the circle J, in the plan, by the horizontal J in section, the circles K, L, M, and N in plan by the horizontals K, L, M, and N of the section. The points of intersection of the radiating ribs in plan with the circular segment I, should be projected vertically to the horizontal I in the section. Those of the circle J, to the horizontal J; those of the circles K, L, M, and N, to the corresponding horizontals in the section. In this manner on each horizontal of the section, are found the points by means of which the curves of the bands may be drawn.
168. To draw the elevations of the stones of the circular part, it is necessary to show their location in plan, and, starting from the semi-pilaster which forms the junction of the portico with the circular walls, the stones are of the same length as those of the straight wall at the back of the portico. For the dentils of the circular cornice, the divisions in plan must also be made. The plan of this temple is shown in Fig. 29.
169. In Plate XXXI is shown a temple that is entirely circular in plan and surrounded by a circular colonnade of Corinthian columns. The ceiling of the domed interior is similar to that of the building shown in Plate XXX, while the ceiling of the narrow porch outside the wall of the building is ornamented with coffers or panels, as is shown on the plan below. This temple is also to be drawn out to the size of 13 x18 inches.
170. The axis of the colonnade is a circle of a radius of three entablatures and twenty parts, this circle being divided into twenty equal parts which give the spacing of the columns. The width of the portico, from the axis of the columns to the circular wall which is thirty parts thick, is one En. The colonnade is raised on a circular platform reached by seven steps, while the floor of the hall is raised one step above this level. The entrance to this hall is a doorway two entablatures seventy-nine parts in height by one entablature and twenty parts in width. Half of the plan shows the arrangement of the columns and shows that their capitals are placed square with the radii which pass through the columns. It will be necessary in drawing an elevation, to draw the plan of all the capitals since each one is seen in a different position, and it is only by means of the plan that the position of the details which make up the capital can be determined. Notice that the plinths of the bases, which, up to the present time have been square in plan, are here circular because their corners would partially block up the spaces between the columns. The other quarter of the plan shows the disposition of the ceiling of the portico, the soffit of the exterior cornice, and the caissons of the cupola.