Read novel on _Conic Section._--Having the form of or resembling a cone. Formed by cutting off a cone at any angle. See line A.
158. _Conoid._--Anything that has a form resembling that of a cone.
159. _Cycloid._--A curve, A, generated by a point, B, in the plane of a circle or wheel, C, when the wheel is rolled along a straight line.
160. _Ellipsoid._--A solid, all plane sections of which are ellipses or circles.
161. _Epicycloid._--A curve, A, traced by a point, B, in the circ.u.mference of a wheel, C, which rolls on the convex side of a fixed circle, D.
162. _Evolute._--A curve, A, from which another curve, like B, on each of the inner ends of the lines C is made. D is a spool, and the lines C represent a thread at different positions. The thread has a marker, E, so that when the thread is wound on the spool the marker E makes the evolute line A.
163. _Focus._--The center, A, of a circle; also one of the two centering points, B, of an ellipse or an oval.
164. _Gnome._--The s.p.a.ce included between the boundary lines of two similar parallelograms, the one within the other, with an angle in common.
165. _Hyperbola._--A curve, A, formed by the section of a cone. If the cone is cut off vertically on the dotted line, A, the curve is a hyperbola. See _Parabola_.
[Ill.u.s.tration: _Fig. 167.-Fig. 184._]
167. _Hypothenuse._--The side, A, of a right-angled triangle which is opposite to the right angle B, C. A, regular triangle; C, irregular triangle.
168. _Incidence._--The angle, A, which is the same angle as, for instance, a ray of light, B, which falls on a mirror, C. The line D is the perpendicular.
169. _Isosceles Triangle._--Having two sides or legs, A, A, that are equal.
170. _Parabola._--One of the conic sections formed by cutting of a cone so that the cut line, A, is not vertical. See _Hyperbola_ where the cut line is vertical.
171. _Parallelogram._--A right-lined quadrilateral figure, whose opposite sides, A, A, or B, B, are parallel and consequently equal.
172. _Pelecoid._--A figure, somewhat hatchet-shaped, bounded by a semicircle, A, and two inverted quadrants, and equal to a square, C.
173. _Polygons._--Many-sided and many with angles.
174. _Pyramid._--A solid structure generally with a square base and having its sides meeting in an apex or peak. The peak is the vertex.
175. _Quadrant._--The quarter of a circle or of the circ.u.mference of a circle. A horizontal line, A, and a vertical line, B, make the four quadrants, like C.
176. _Quadrilateral._--A plane figure having four sides, and consequently four angles. Any figure formed by four lines.
177. _Rhomb._--An equilateral parallelogram or a quadrilateral figure whose sides are equal and the opposite sides, B, B, parallel.
178. _Sector._--A part, A, of a circle formed by two radial lines, B, B, and bounded at the end by a curve.
179. _Segment._--A part, A, cut from a circle by a straight line, B. The straight line, B, is the chord or the _segmental line_.
180. _Sinusoid._--A wave-like form. It may be regular or irregular.
181. _Tangent._--A line, A, running out from the curve at right angles from a radial line.
182. _Tetrahedron._--A solid figure enclosed or bounded by four triangles, like A or B. A plain pyramid is bounded by five triangles.
183. _Vertex._--The meeting point, A, of two or more lines.
184. _Volute._--A spiral scroll, used largely in architecture, which forms one of the chief features of the Ionic capital.
CHAPTER IX
MOLDINGS, WITH PRACTICAL ILl.u.s.tRATIONS IN EMBELLISHING WORK
MOLDINGS.--The use of moldings was early resorted to by the nations of antiquity, and we marvel to-day at many of the beautiful designs which the Ph[oe]necians, the Greeks and the Romans produced. If you a.n.a.lyze the lines used you will be surprised to learn how few are the designs which go to make up the wonderful columns, spires, minarets and domes which are represented in the various types of architecture.
THE BASIS OF MOLDINGS.--Suppose we take the base type of moldings, and see how simple they are and then, by using these forms, try to build up or ornament some article of furniture, as an example of their utility.
THE SIMPLEST MOLDING.--In Fig. 185 we show a molding of the most elementary character known, being simply in the form of a band (A) placed below the cap. Such a molding gives to the article on which it is placed three distinct lines, C, D and E. If you stop to consider you will note that the molding, while it may add to the strength of the article, is primarily of service because the lines and surfaces produce shadows, and therefore become valuable in an artistic sense.
THE ASTRAGAL.--Fig. 186 shows the ankle-bone molding, technically called the _Astragal_. This form is round, and properly placed produces a good effect, as it throws the darkest shadow of any form of molding.
[Ill.u.s.tration: _Fig. 185. Band._]
[Ill.u.s.tration: _Fig. 186. Astragal or Ankle Bone._]
[Ill.u.s.tration: _Fig. 187. Cavetto. Concave._]
[Ill.u.s.tration: _Fig. 188. Ovolo. Quarter round._]
THE CAVETTO.--Fig. 187 is the cavetto, or round type. Its proper use gives a delicate outline, but it is princ.i.p.ally applied with some other form of molding.
THE OVOLO.--Fig. 188, called the ovolo, is a quarter round molding with the lobe (A) projecting downwardly. It is distinguished from the astragal because it casts less of a shadow above and below.
THE TORUS.--Fig. 189, known as the torus, is a modified form of the ovolo, but the lobe (A) projects out horizontally instead of downwardly.
THE APOPHYGES (p.r.o.nounced apof-i-ges).--Fig. 190 is also called the _scape_, and is a concaved type of molding, being a hollowed curvature used on columns where its form causes a merging of the shaft with the fillet.
[Ill.u.s.tration: _Fig. 189. Torus._]
[Ill.u.s.tration: _Fig. 190. Apophyge._]
[Ill.u.s.tration: _Fig. 191. Cymatium._]
[Ill.u.s.tration: _Fig. 192. Ogee-Recta._]
THE CYMATIUM.--Fig. 191 is the cymatium (derived from the word cyme), meaning wave-like. This form must be in two curves, one inwardly and one outwardly.
THE OGEE.--Fig. 192, called the ogee, is the most useful of all moldings, for two reasons: First, it may have the concaved surface uppermost, in which form it is called ogee recta--that is, right side up; or it may be inverted, as in Fig. 193, with the concaved surface below, and is then called ogee reversa. Contrast these two views and you will note what a difference the mere inversion of the strip makes in the appearance. Second, because the ogee has in it, in a combined form, the outlines of nearly all the other types. The only advantage there is in using the other types is because you may thereby build up and s.p.a.ce your work better than by using only one simple form.