return of the engineer-in-chief, together with an index register, should have a proper register made of all the documents returned to him. These documents should be secured against accident by depositing a certified copy of each in a suitable place or places for public

purposes.

The conveyance of an allotment or parcel to a purchaser should recite and include a copy of the maps, measurements, and other parcel documents, certified copies of which should pass to the purchaser, as the description of the grounds. By this means the purchaser may be put into formal possession without going on the grounds, and restrained in case of encroachment on the surrounding parcels or public reservations. The documents so to pass would furnish, ever after, a complete description and the means of identification of the parcel or plot conveyed.

INTAKE OF LAND FOR RAILWAYS, ETC.

After determining the 'centre line' levels, and extent of works, it is necessary to make a survey of the 'intake of land' required for the purpose of the railway, &c., &c. In the field operations for the working section,' the centre line should be pegged at measured points, usually about sixty-six to one hundred feet apart. These peg points are taken up in the levelling of the centre line, and are shown as level points on the working section; their reduced levels should be inserted in the proper column on the field-book of levels. The section should show the extent of works, or the grade lines for the earthworks, and also the reduced level for the grade line, at each peg point. The inclination of the side slopes should be also shown. This information should be in the hands of the surveyor making the survey for intake, and also a working

plan showing the pegged centre line, intersected detail, &c. The surveyor should take levels, and other measurements, in a transverse line at each peg, to determine the surface inclination and limits of intake.

m

Filling

721

Fig. 48.

m

1

These measurements may be made, and the half-widths from centre line computed, and laid down as follows:Let m m' (fig. 48) represent the surface line on cross section (determined by the surveyor in the field); h the centre line at level point; h n the depth of cutting, or height of filling, as the case may be; n b half the width at grade level m b side slope, produced to intersect the vertical of

h in c.

The level of a point din the transverse line

Cutting

d

m

m

ν
t

h

n

hd should be found,

and the distance of the point from h measured. Now, if there be no difference of level between the points h and d,

hc

as in (1), we have × nb = hm, the surface half-width

пс

to side slope. If, however, there be a difference of level between the points h and d, such as th (2), the surface half-widths will not be equal. These may be found as follows:

The surface distance hd, and the corresponding vertical height th, are given. Then dt = (dh2 - ht2)1. By taking dt as a half-width on the level, the corresponding depth tr to intersection of side slope may be found from the

пс

formula x d t = tr. From this hr may be readily

nb

found; and from the similar triangles hrd, h cm, the surface distance h m may be found from the proportion rhhd ch: hm. In like manner, the surface half

width h m' may be found.

If the inclination of the surface line of half-width be not the same as in (3), the side right-angled triangle htd should be found as above, and the surface line h m' td x h m

and vm' =

hd

htxhm' measured. Then hv= hd From these vr may be computed as above, and rc (=m'n) readily found. Now m' may be treated as a centre line point for a depth m'x. The triangle m' t' d' and the depth ť'z should be found in the same manner as the triangle htd and depth vr were found. Then m'm should be ascertained for the depth m'x, as explained in the second case. The surface half-width (h m' + m' m) should be ascertained in this manner. The model scale (illust. 82) may be, in many cases, conveniently used for this purpose.

To the surface half-widths, ascertained as above explained, the widths for fences, drains, &c., should be added to find the extreme half-width, terminating in the boundary line of the intake. The results thus arrived at do not, however, hold good on sidelong ground when the surface inclination varies on the consecutive cross-sections, at peg points on the centre line. To bring out strictly correct results the transverse half-width section line should be selected according to the surface configuration, and not arbitrarily at peg points. It will appear, on a little consideration, that on sidelong ground the halfwidths for opposite sides of the centre line should not be referenced to the same point in that line. The trans

verse lines for the half-widths will be most conveniently measured in vertical planes, perpendiculars to the vertical plane of the centre line at the reference point. In these determinations of the half-widths it should be found that the straight line joining the outer extremities of each consecutive pair of half-widths laid down shall be a straight line in the surface of the ground.

A much more exact mode of laying down the boundaries of intakes for railway or like purposes will be explained in connection with 'intakes,' Chap. VII.

The part of the areas of the several parcels included in the intake may be computed separately from surveys, and the results verified by taking the sum of the products of the successive mean half-widths, multiplied into their respective peg distances, or otherwise, by the Simpsonian rule.

SURVEYING SUBMERGED DISTRICTS.

When it may be desirable, for engineering or other purposes, to ascertain the surface configuration of a submerged district, such as a river bed, the bottom or bed of a lake, estuary, bay, &c., a hydrographical survey should be made in such manner as will furnish data for the representation of the features on a map. A preliminary or base map of the water margins and adjacent dry ground, if one already made be not procurable, should be made from a proper survey of the dry ground district. The prominent features and well defined surface objects should be clearly shown on this map. As the surface of the bottom is not generally visible, its configuration must be ascertained by referring numerous points in it to a known plane, such as the surface of still water. If the water surface be inclined, or not steady at the same level, as in a river with an appreciable current, or a tideway where

the surface fluctuates rapidly through a considerable range at the same point, the inclination of the river water surface should be obtained by levelling, and the fluctuations due to tide flow by observations on a tidal gauge erected, for the purpose, at suitable places.

The depth of the water from surface to bottom is generally obtained with a wire, or cord, weighted at the lower end. This is usually called a 'sounding lead and line,' and the point a 'sounded point.' The depth is called the sounding' of the point.

The bottom of the 'lead' is generally made concave, and filled with some stiff, sticky, and greasy substance, for taking up loose matter at the bottom, such as sand, &c. If the depth be less than 100 feet it is preferable to use a wire chain, or steel tape line, as a hempen cord varies its length with the degree of saturation.

The horizontal position of the sounded point may be determined from land or on water. If from land, it will be found convenient to observe simultaneously at two distant known points on land the surveyor's signal flag. The contained angle at the sounded point should not be less than 30°. The position may, however, be more conveniently determined by measuring with the sextant at the sounded point the angles to three known land objects, or it may be determined, though less accurately, by measuring the magnetic angles of the lines to two or more well defined land objects intersecting in the sounded point.

If the position of two remote sounded points be found by any of the methods just alluded to, the position of intermediate points in the straight line may be found by computation on the lapse of time from starting at an extreme or other point to the arrival at the next intermediate or the other extreme point-the rate of travel