## Engineering Drawing

In this section we purpose explaining, chiefly by appropriate illustrations, the methods of delineating those subjects which form more particularly the branches of what is generally designated as Civil Engineering, whether these be shewn as plans, maps, elevations, or sections. As the rules, or more properly the methods, to be observed in copying subjects of pure outline, where the drawing-board and instruments are available, will obviously be very similar to those which we have already detailed in the First Section, we do not consider it i>eceissary to multiply examples of outlines, such as bridges, &c. The pupil desirous of studying Civil Engineering as a profession will find numerous examples which may serve as 4 copies' in the more technical and strictly professional works which it will be his duty to consult. We shall content ourselves with giving one or two examples of the method of setting out copies of bridges, <&c.

Example 1, fig. 1. Bisect any two of the piers, as ab, cd, in the points ' a and c. Draw lines am, cd; put in the piers ; divide ac into two equal

portions at the point h; parallel to cd draw hi; measure to i This will be the centre of die arch. In like manner the aqueduct arches in

Example 2, fig. 2, may be drawn; the lines d, c, a, 5 being the lines of the piers; g the centre of the under, and h that of the upper arches. The various parts of an arch are shewn in

Example 3, fig. 3, where db is the (span' of the arch; ed its 'rise

The method of delineating the various features of a country or district in a map is shewn in

The exterior or upper curve d is the 'crown* of the arch, called the 'ex*-trado8.}

Example 4, fig. 4, is an elevation of bridge with semi-elliptical arch. For method of describing this form see Practical Geometry.

Example 5, fig. 5, is elevation of the timber framing or 'centering' of a bridge.

The method of delineating the various features of a country or district in a map is shewn in