## So To

#ie plan is fig. 20 to be enlarged twice, as in fig. 19. Irregular portions of maps may be copied by adopting offset lines, as in

Example 21, fig. 21, which represents part of a river, which is required to be copied and enlarged as below. Draw any line cd; from any scale set off distances, as c^r = 50, gh = 60, and so on. Next draw a line, as po, corresponding to cd; fromp set off distances corresponding to those in cdf but taken from a scale larger than that of cd. From the same scale as that from which the measurements on cd were taken, measure the lines drawn at the various points at right angles to cd to where they touch the outline of the lowest side of river, 9§,<7 = 40. Make the line t the same distance, but taken from its proper scale; by proceeding thus, points will be found, by tracing through which, an outline will be obtained equal to that of the copy. The pupil should extend this principle of copying irregular figures, by which he will be enabled to judge of its utility in practice.

fig. 22

few examples of the lettering attached to P jL H, I S K OF

maps and plans.

Example 22, fig. 26, shews the compass-mark in plans, by which the directions are obtained. The fleur-de-lis always points to the north.

Example 22, fig. 26, shews the compass-mark in plans, by which the directions are obtained. The fleur-de-lis always points to the north.

Example 23, fig. 27, represents the plan of part of a district through which a road aft is to be cut. The section of this is in

fig. 27.

Example 24, fig. 28. The parts filled in with small dots represent hollows filled up ; the cross-lines point where a cutting is made. The horizontal line cd is termed the ' datum line.' See article 1 Levelling* in, the work on Practical Mathematics in this series.

fig. 29.

Example 25) fig. 29» represents a section of road, shewing method of delineating it. -

Example 26, fig. 30, represents the rocks at the side of a section of a railway cutting.

Example 26, fig. 30, represents the rocks at the side of a section of a railway cutting.

method of delineating an embank-

fig.32.

Example 27, fig. 31, represents t ment faced with rubble masonry.

Example 28, fig. 32, represents a breakwater formed of large stones thrown together, sloping outwpj-ds to resist the action of the waves.

Example 29, fig. 33, is the section of a stone pier, where a a is the face toward harbour; bb that to the sea; the interior is filled with round stones, as cc. The plan of a retaining wall is shewn in method of delineating an embank-

fig.32.

fig. 33.

Example 30, fig. 34, where Jcc is.the stone facing; d the stones used for filling up.

Example 31, fig. 35, represents the footings b of a pier of a bridge resting on a sand foundation at a.

fig. 35. fig. 36.

- Example 32, fig. 36, represents piles of wood driven into the ground, supporting masonry. A section of a coffer-dam in a bed of 1 beton' is shewn in

fig. 37.

Example 33, fig. 37, where cc is the mass of masonry, resting on the mass of beton; dd represents mud; ee the main piles and 'wales,' and ff the cross-pieces ; b represents the clay-puddling between the piles, which serves to "keep out the water from the interior. For explanation q£ the various terma here used, see treatiseon Mechanical and Civil Engineering.

B 10 to 30

B 10 to 30