Imagens das páginas

and the experiments made with the instrument will show how very important it is to the country to have the public roads constructed and maintained on true principles.

In some instances metal rails are laid on the sides of turnpike roads, with the same undulations and rates of inclination as the road; yet on these railroads a horse will usually perform as much work as five or six horses will do on the common road. This great difference in the useful effect of horses can alone be attributed to the friction of the road surface exceeding that of the metal rails; for the friction of the axles of the waggon will be nearly similar, and the resistance of gravity, arising from the inclinations, is, in this case, the same; hence the superiority of the one road over the other depends entirely on the surface.

The greatest resistance which a horse has to encounter, when in draught on turnpike roads, arises from gravity, which begins to act the moment the road ceases to be horizontal; and when the inclination exceeds one in thirty, which it often does, the additional power required is very great, as may be seen by the table of corrections; at the same time, the power of the horses is from the same cause much diminished. It is, therefore, the more necessary that the surface of the hills should be hard, solid, and composed of such materials as the wheels of carriages cannot penetrate.

By making experiments with this instrument on every part of a turnpike road, both in summer and winter, and forming an exact table, showing the resistance of the surface, and the materials with which it is repaired, a complete register would be had of the state of the road; and any improvement or falling-off in the general management of the repairs of each part would be clearly perceptible, as also the amount of such improvement, or the reverse.

The following is an extract from the Appendix of this Report, containing Mr. Macneill's description of the experiments referred to: —


For the purpose of ascertaining the draught up different hills, with different velocities, the instrument was attached to a common stage coach, which weighed 18 cwt., exclusive of seven passengers. Stations were marked out on different parts of the road, of which the inclinations and the lengths were accurately determined, and the time of passing over each was ascertained by means of a stopwatch.

The results of these experiments are detailed in this table.

The first column contains the number of each experiment; the second, the rate of inclination of the hill; the third, the number of observations made on each; the fourth, the length of the hill or inclined plane, in feet; the fifth, the number of seconds in which the carriage was drawn up the hill; the sixth, the corresponding velocity in feet per second; the seventh, the velocity in miles per hour, calculated to the nearest quarter; and the eighth column contains the corresponding draughts, or force applied, in pounds.

Thus, in the first line of the first experiment, where the inclination of the hill was one in fifteen and a half, and the velocity three miles and a half per hour, the draught was 271 lbs.; and when the velocity was increased to twelve miles per hour, as shown in the fourth line of the

* Table No. 1. contains a detailed account of the experiments made on the Holyhead Road, and Table No. 2. the corrections for gravity according to the inclinations of the road.

same experiment, the draught was also increased from 271 to 325 lbs.

The part of the roads elected for these trials was of an uniform surface, the resistance of which was previously ascertained by drawing a waggon over it, to be an average between the worst and most improved parts of the Holyhead road; and although the velocities are not so varied, or so high as might be wished, yet several conclusions may be drawn from these experiments, of considerable importance in road engineering; one of which is, that the draught of a stage coach on a common turnpike road increases in a less ratio than the velocity increases, and not as the square of the velocity, which many persons have supposed, as is found to be the case in the steam carriage on a rail-road. From this it appears, that the resistance, arising from friction, of a steam carriage on a rail-road, and the resistance of a stage coach on a good turnpike road, are governed by the same laws of motion; and that whatever advantage may be gained by a quick transport of passengers, by means of a steam coach on the former, may also, probably, be attained by the same means on a well-made turnpike road.

[merged small][table]
[merged small][table]
« AnteriorContinuar »