NOTES. NOTE A. Page 50. HOLYHEAD ROAD. STOWE VALLEY IMPROVEMENT. Investigation of the best Plan to be adopted for improving the Road through Stowe Hill Valley. By John Macneill.* In a great public work of this kind, where a considerable sum of money is to be laid out, it becomes of the greatest importance to ascertain not only what would be the best plan to be adopted, but also to what extent it should be carried, or, in other words, what sum of money should be laid out on the works so as to produce the most advantageous result. Without altering the entire line of road, as originally proposed by Mr. Telford, which would unquestionably have been the wisest measure, there does not appear to be any means of effecting an improvement of the present line of road, except by embanking across the valley, or lowering the ridges, or by both. It is evident that each of these plans will admit of * This paper, which was prepared for the Parliamentary Commissioners, was, with their permission, read at the Institution of Civil Engineers. This and the following notes have been furnished by Mr. Macneill. different degrees of perfection, according to the sum of money expended on the works; but it is not evident which of these plans is the best, nor does it follow that the same sum of money would produce an equally beneficial improvement, if laid out in raising the valley without lowering the summits, or in lowering the summits without raising the valley. In order to solve this important problem, and to arrive at an accurate result in this and similar investigations, it is necessary to know correctly the expense of horse labour under the varying circumstances of velocity and force of traction on different inclined planes, and also the draught of carriages, and the ratio of the increase of draught in consequence of increase of velocity. By the experiments lately made on the Holyhead Road by order of the Parliamentary Commissioners, these circumstances have been accurately ascertained from practical experience, which has enabled me to deduce the necessary formulæ from actual practice, without having recourse to theoretical investigations or abstruse calculations. To go into the detail by which these formulæ were deduced would be in this place unnecessary; it is sufficient to state that correct tables have been calculated from these formule, which show the expense of drawing a given weight with a given velocity over every rate of acclivity and declivity, and length of inclined plane. By means of these tables the expense of drawing a ton weight over any line of road may be determined with great accuracy. Hence all that is necessary in the present investigation is, to calculate by the tables the expense of transporting a ton weight over the existing line of road, and also over the proposed improvements. The difference will be the saving in expense of drawing one ton with the given velocity over the proposed improvement. This, multiplied by the number of tons that pass over the road each day, and by the number of days in the year, will give the annual saving, which, compared with the interest of the money necessary to be expended in making the improvement, will clearly show whether the saving in horse labour is commensurate with the proposed expense. By applying the same criterion to each of the proposed plans, it will at once be made evident which of them should be adopted, as that which would produce the most beneficial result at the smallest expense. By this method, which is new, and founded on correct principles, I have endeavoured to determine the most advantageous method of improving the present line of road across the Stowe Hill Valley from the sixty-fifth milestone to the Crown publichouse at Foster's Booth, a distance of two miles. PLAN, NO. I. By this plan it is proposed to leave the present road near the sixty-fifth milestone, and to pass at an elevation of twenty-seven feet lower than the present road: from thence it would descend through a natural valley at a rate of inclination of one in thirty to an angle in the Lichborough and Northampton road: from this point it would pass in a straight and horizontal line, at an elevation of fifty feet over the brook, to the junction of the present road; here it would cross the road, and, skirting along the side of the hills at an inclination of one in thirty, running nearly parallel to the present road, and at about fifty yards distance from it, would pass the summit at twenty-seven feet lower level, and join the present road, near the Crown public-house. |