adjoining the road till they can be otherwise disposed of.

Constant attention on the part of a road surveyor is necessary to keeping hedges clipped, and the branches of trees in the fences lopped. The hedges should be cut so as to be as low as they can be kept without making the fence unfit for confining cattle within them. The superior condition of roads, at all times, crossing uninclosed land, shows how valuable a full exposure to the sun and wind is, in contributing to the preservation of roads.

The trustees of a turnpike road should require their surveyor to lay before them, at the commencement of every year, an estimate of the work he proposes to perform in the ensuing year. In this estimate every particular should be specified; namely, the quantity of materials to be provided, the prices to be paid for them, the labour to be employed, &c., &c. The surveyor should be required to make up an account at the end of every month, of the money received and paid by him; and he should also make up an annual account, showing the particulars of the year's expenditure, the quantity of materials bought and carried to the road, the sums paid for day labour, for task work, and for cartage, &c.

In some cases the practice has been introduced of employing a pay-clerk to pay for all the road expenses, in order to relieve the surveyor from all trouble about pecuniary matters, and at the same time to remove as much as possible all temptation to swerve from his duty. This prac

tice has been attended with the best effects, and cannot be too strongly recommended.

CHAP. XI.

ROAD INSTRUMENTS AND TOOLS.

THE principal instruments employed in surveying and laying out roads are theodolites, spirit levels, and sextants.

Theodolites.

Theodolites in careful and experienced hands are the best instruments for laying out a road, and for taking horizontal angles and intersections. The rates of inclination can be determined at once by means of the vertical arch, without any measurement by the chain being required: they are decidedly the best instruments.

Theodolites are made of various sizes and prices; but those that are five inches in diameter, and cost about 177. are the most suitable for road purposes.

These instruments are divided on the limb into spaces of thirty minutes, and by means of a vernier, single minutes can be read off with great precision.

They are furnished with a good telescope and

spirit level, besides two levels on the limb set at right angles to each other, and a magnetic needle or compass in the centre, which is of use in getting the magnetic bearing of any line in the survey, or of taking the bearings independent of the divisions on the limb.

The theodolite is used in the following manner in surveying a road.

When the line of direction is fixed upon, the theodolite is set up over the first point in the survey it is then adjusted by means of the spirit levels, so as to be perfectly level. The eye piece of the telescope is moved in or out until the hairs are seen distinctly; and the object glass is adjusted to distinct vision according to the distance of the levelling staff from the instrument. Zero on the limb is then brought to coincide with zero on the vernier plate, and the limb and plate are then clamped together. After this is done, the whole head is turned round, until the north point on the compass box coincides with the north point of the needle. The limb is then screwed fast, and the vernier plate unclamped and turned round until the staff is seen through the telescope: the vernier plate is then clamped, and the observation completed by turning the tangent screws of the limb and of the vertical arch, until the centre

of the vane exactly corresponds with the centre of the cross hairs in the telescope. The degree and minute on the limb and vertical arches are then read off and entered in the field book.

The distance from the instrument to the staff is then measured by the chain, and all offsets are at the same time measured and entered in the book. The length of the distance line is then carefully entered, and the theodolite removed and again set up directly over the point previously occupied by the levelling staff: this may be done by means of the plumb line usually attached to the instrument. The next operation is to adjust the instrument perfectly level, and to send the staff back to the point originally occupied by the theodolite. The vane having been previously adjusted to the exact height of the centre of the telescope, the head of the instrument is then turned round until the staff is seen in the field of view of the telescope: the head is then clamped, and the bisection made by means of the tangent screw; the vernier plate still remaining steadily clamped to the limb. The vertical arch is then examined, to see if the degree and minute corresponds with those previously observed: if not, the first observation must be repeated. The vernier plate is then unclamped, and the telescope turned round towards the next line of direction