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times only one staff is used, in which case it is removed from the first to the second station after the observation is made. When very great accuracy is required, the level is set up by measurement exactly in the centre between the two staffs, for by this means the errors of adjustment and any slight deficiency in the instrument are compensated and mutually destroy each other.
The small pocket sextant is a most useful instrument in making road surveys; after a little practice, it can be used with great facility, and will be found a superior instrument to the common surveying needle, and much more accurate, besides affording the most expeditious method of making surveys of any yet known.
In some parts of the clay districts, a narrow spade, considerably curved in the blade, technically called a grafting tool (Plate VII. fig. 10.), is much used, particularly in cutting deep drains in stiff clay.
The best description of shovel for road work is pointed in the blade, and has a curved handle to allow the workmen to bring the blade flat to the ground without stooping. (See Plate VII. fig. 13.) Trucks.
When metal rails can be laid down, the truck or small waggon is the best description of carriage for removing earth. A drawing of one of these is given in Plate VII. figs. 11 and 12: they usually hold a cubic yard of earth. The body is generally made of elm, the frame of oak, and the wheels and axles of iron.
Two descriptions of hammers, which are the most useful in road works, are represented in Plate VII. figs. 15 and 16. The handles should be flexible and made of straight grained ash, particularly those used for breaking pebbles: the small hammers should have a chisel face, and the larger ones a convex one, about five-eights of an inch in diameter. Those made of cast steel are the best; and though expensive in the first cost, they wear much better than wrought-iron ones, and very seldom break at the eye.
Pronged shovels are useful for filling stones, when broken, into carts or barrows: a drawing of one is given in Plate VII. fig. 7- A man is enabled to lift stones with much greater ease and more expeditiously with one of these shovels than with a common one; besides, he lifts them without taking up any earth with them.
Scrapers are sometimes made of wood shod with iron, but those made of plate iron are preferable: they should be six inches deep, and from fourteen to eighteen inches long in the blade, according to the materials of which the road is composed; the softer and more fluid the mud, the longer the scrapers should be; they should be turned a little round at the ends, to prevent the mud from escaping. The best scrapers are made of old saw plates, stiffened on the back by a rib of wrought iron, or by riveting the plate to a board of elm, cut to the proper width and length, and about half an inch thick.
Patent Road Scraper.
The following is a description of a patent road scraper: —
"This machine consists of a series or row of scrapers placed in a frame, and mounted on wheels; it is worked crosswise on the road, and deposits the dirt or dust on the side.
"The machine is easily used by one man, and cleans above a mile of road per day, or about five times as much as can be done with the common scraper, and the work is better performed.
"The advantages from the use of this implement may be stated shortly as follows, and will be readily appreciated by surveyors : —
"1st. Improvement of the surface of the roads, which cannot be kept hard and firm unless the road be frequently scraped.
"2d. The facility afforded to fast travelling, by removing a great obstruction to the progress of carriages.
"3d. The preservation of the roads, by removing the dirt, which absorbs and retains water on the surface.
"4th. Assistance rendered to the surveyor, by enabling him to take advantage of favourable periods of weather for cleaning his roads.
"5th. The saving of money, which will be applied in strengthening or otherwise improving the roads.
"Wherever it has been tried, the machine has given great satisfaction, and the patentees are willing to send machines on trial." *
* Messrs. Bourne and Harris, of Ilchester, Somersetshire, are the patentees of this machine.
The following letter respecting it is from the engineer of the Holyhead Road: —
"Sir, Holyhead, 3d March 1837.
"On receipt of your letter this morning, I spoke to the foreman, and also to the labourer who attends to the road round this harbour, as to the comparative merits of the old and new scrapers: both of them gave the preference to the latter, as doing its work quicker and better than the former.
"When last I was at Corwen, Hugh Roberts the inspector told me that two of his men had had a dispute as to which of the scrapers was the best; they set to work, one with the common, the other with the patent scraper, and the result was, that the patent scraper took the dirt off cleaner than the other, as was proved by that part of the road on which it had been used remaining for a longer time without requiring to be scraped again than that part on which the common scraper had been employed.
"I am, Sir,
"Your most obedient servant,
"John Pro Vis."
These instruments have been long used in Scotland, where they are called plashing tools: they are made of different sizes; that represented in Plate VII. fig. 14. is the most useful. When a labourer is a little practised in the use of them, he can trim a hedge as well as a gardener with a pair of shears, and much more expeditiously. They should be made sufficiently light to enable a man to use them with one hand, and care should be taken by the maker that they are properly balanced on the handle, otherwise a workman will not be able to wield them with proper effect. The great error in making these instruments in England is that of making them too heavy, and curving the blade too much.
Working levels are absolutely necessary in laying out new works, and in repairing old roads. These instruments are easily used by common workmen. One of the best kind of these levels is represented in Plate VII. fig. 8., in which ABC represents the level, upon the horizontal bar of which are placed four gauges, a, b, c, d, made to move perpendicularly to the line A C, in dove-tailed grooves cut in the horizontal bar. When any of these are adjusted to project a proper depth below the line A C, it may be fixed by a thumb screw, which will retain the gauge in the desired position.
Fig. 9. shows a section of the horizontal bar drawn to a larger scale, as marked upon the edge