1438

THEORY AND PRACTICE OF ENGINEERING. Book II.

To facilitate the opening of a door or casement inwards, the arch is constructed in themanner shown in the accompanying diagram: in France this method was first practised atMarseilles ; these voussoirs or vault headings are formed by right lines intersecting threearcs of circles: the first is shown on the plan at E K, in the elevation at E S P, and on theprofile or section at PE; the second is the arc RTE, and the third the arc RO:from the point R on the elevation draw the line R V, perpendicular to the arch ESP;

Fig . 2CC0.

Fig. 2501

Fig. 2504,

Fig. 2505.

Fig. 2502.

JOINTS ,

/ 2503.

Fig. 2509.

Fig. 2512.