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Fig. 818. Doric triglyph and frieze, with the usual accessories. AB gives the boundary of shadow on the femora of the triglyph, AC the boundary of shadow on the light sides of the glyphs, and AD of the shadow of the corona on the frieze. 2473. Fig. 849. is a skeleton representation
Fig. 819. of a three-quarter column, forming part of an arcade. The abacus is the mere block of material AK. In the plan ab shows the length of the line of shadow A B, and is determined by the vertical bB. In the same way, CD is found by cd and the vertical dD. KG is the representation of kg on the plan, and by a vertical from g the line GH is also determined; H giving also by the horizontal line FH, in which H is already found, the situation of shadow of the point E of the abacus, as also by a vertical from f. LMN are places of the shadow of the column on the impost moulding of the arch, whereof two
а correspondent points are seen in 1 and n.
2474. The form of shadow of the console in fig. 850. will be seen on inspection to have been found from the lines aa, cc, dd, &c. on the elevation, corresponding with aa, cc, dd, &c. on the section, all which are parallel to the direction of the light, and sufficiently explain themselves.
2475. Fig. 851. is the elevation and section of a hemispherical niche, wherein are shown the shadows cast thereon by the vertical wall in which it is placed. Through the centre O draw DD at right angles to the direction of the light, and from O draw OA parallel to the direction of the light: A will be found the point in the wall casting the longest shadow. Produce AO indefi. nitely; and from a, the corresponding point in the section to A on the elevation, draw aa', parallel to it, which will cut the surface of the niche in a'. Draw the horizontal line a' a' cutting A0 produced in a'", and all will represent in the shadow the point A in the cir. cumference. Take any other point B in the edge of the niche, and by means of a line drawn therefrom horizontally we have the correspondent point b of B in the section. From B draw in the direction of the light the line BV" b'', cutting DD on the diameter in b'"; transfer the point b'' in the elevation to b in the section, and draw bb' in the direction of the light indefinitely. Then with Bb!" as a radius from b as a centre, describe an arc cutting bb'in b'; and from b' draw the horizontal line b' b'', cutting Bb" produced in b'', and b' will be the point in the shadow corresponding to B in the elevation. To avoid the confusion which
wherein the upper story is occupied by an attic in the centre, against which, on each flank, the sloping roof is terminated. aa on the plan in the direction of the light, produced to intersect the hip at b, gives, by a vertical to B on the elevation, the Jirection BB of the shadow thereon ; and BB cut by A A in the direction of the light, the length BA of the line of shadow, which may, by letting fall the vertical Aa, determine the length aa on the plan. The line of shadow ac is determined by letting fall a vertical from C, where the line of shadow is intercepted by the hip of the roof; and from c the shadow will be found on trial to return as shown in the diagram. E and D on the elevation are found, as seen in previous examples, in ee, and d on the plan, and their shadows at e'e' and d'. 2480. What is called an attic base is given in plan and elevation by fig. 856.
The me thod of obtaining the shadows thereof in plan and elevation is now to be explained. It is an example which constantly occurs in architectural subjects, and should be well studied and understood. The operations requisite for obtaining a representation of the lines of shadow of the different mouldings in this example depend upon the principles developed in the preceding subsections. The lower portion of the figure exhibits the plan, and the middle portion the elevation of the attic base in question. The uppermost portion of it presents three sections of the mouldings of the base in question cut in three different places parallel to the direction of the light. This last portion of the figure is not absolutely necessary, inasmuch as the profiles in question might have been obtained upon the elevation; but we have preferred keeping it separate to prevent a confusion of subsidiary lines. There is moreover another advantage in thus separating the parts from each other, namely, that of immediately and more distinctly seeing the lines at each selected place, in which the rays of light separate the parts actually in light from those in shadow; and where the student is likely to meet with
Fig. 856. matters of perplexity, nothing should be left untried to save his time, and, what is often more important, his patience. The mode to be adopted is as follows:
Make on the plan any number of sections a'a'a'a', b'UU'b' in the direction of the light, and draw on the elevation the corresponding sections aaaa, bbbb. LL being the direction of the light, draw parallel thereto tangents to the curves of the convex mouldings, and the bounditries of their shades will be obtained, as will also those of their shadows, by continuing them from such boundaries till they cut the other parts in each section, as will be more especially seen at cc. It will be recollected that in our first mention of the projected representation of the line of light and shadow we found that it was an angle of 54 44' of the diagonal of a cube. This angle is set out in xyz on the plan. We have therefore another mode of finding the boundaries of shade and shadow on the moulding, by developing the sections a'a'a'a', b'b'U'b', &c., as at A, B, and C, and drawing tangents yz to the convex mouldings for
boundaries of shade thereon, and continuing them, or otherwise, for the other parts, as shown in the diagram.
2481. In fig. 857., which represents the capital of a column, a similar method is used to that last mentioned for obtaining the shades and shadows, by means of a'a'a'a' and b'b'b'b', which are shown on the elevation by aaaa and bbbb. We apprehend this will be understood by little more than inspection of it.
It is obvious that the means here adopted for obtaining the lines of shadow are precisely similar to those used in the preceding example. In this, however, the sections of the capital parallel to the direction of the light are made on the elevation, and it will be seen that many of them are not required to obtain an accurate boundary of the lines of shadow sought; for after having obtained those points from which the longest shadow falls, and on the other side those where the line of shadow commences, a curve line of an elliptical nature connects the points found. If the drawing to be made be on a large scale, it may then be worth the architect's while to increase the number of points wherefrom the shadow is to be projected, so as to produce the greatest possible accuracy in the representation.
2482. The shadows of an Ionic capital are given in fig. 858. The shadow of the volute on the column is obtained by any number of lines A A, BB, CC, &c. from its different
Fig. 858. parts and verticals from their corresponding ones aa, bb, cc, &c. on the plan, and similarly the shadow of the capital on the wall. In this example, as in those immediately preceding, the employment of sectional lines parallel to the direction of the light is again manifest. The use of them is most especially seen in the example of the Corinthian capital whieh follows. As a general rule, it may be hinted to the student of sciography, that in the difficulties that may occur, they will be most expeditiously and clearly resolved by the use of the sectional lines, whereon we have thought it proper so much to dilate.
2483. The Corinthian capital in fig. 859. will require little more than inspection to understand the construction of its sciography; and all that we think necessary to particu. larise are the developed projections A, B, C, D, E, F of the abacus and the leaves, whereon the termination of the shadows at angles of 54° 44', as explained in fig. 856., give their respective depths on the elevation.
There is another method of arriving at the result here exhibited, by drawing sectional lines parallel to the direction of the light through the different parts and leaves of the