road from Worcester to Ryan summit, upon an undulating line, or upon a line with ascending and descending grades of 80 feet. The difference of cost between such a line as we are about to describe, and that upon which the first estimate was predicated, will be about $150,000. This is undoubtedly a large sum to be saved, in grading a piece of road of only 14 miles in extent. But there are so many disadvantages attending a road constructed upon this principle, that the great saving in cost becomes, comparatively, a small consideration. It is proper to remark, that the calculations of the cost of grading this line, are made upon the supposition that the fillings are to be diminished in the same manner that it is proposed to reduce the cuttings; or in other words, that the undulations are carried both above and below the uniformly ascending grade upon which the first computations were made. If, as in the case of the route by Ryan summit, we adopt a line, say, in no instance exceeding 40 feet per mile, but generally at 35 feet, and undulating upon it in such a manner that the grade shall never fall below this line; then the height of the summit will be increased, virtually, by an amount equal to the total sum of descents, viz. 138 feet. But as the object of grading the road upon this principle is to save expense in the cost of construction, and upon this line the cuttings and fillings being nearly equal, that is to say, they are in the ratio of 1 to 1.04, we should, to derive all the benefit from it in this respect, which this mode is susceptible of yielding, extend the grade below the line before referred to, in such a manner, that the quantity of fillings may be diminished, as well as that of the cuttings, if it is carried below, the amount of the descents will be increased 231 feet, and equating these two sums, 138 feet and 231 feet at the rate of 18 feet per mile, we find them equivalent to 7.68 miles, and 12.83 miles, respectively, or enumerating them thus: Upon the lesser, and constantly ascending grade 13.82 miles. Undulating above the uniformly ascending grade 21.47" above and below 66 26.65 66 or, in other words, the cost of transportation upon this line, by these three modes of grading, will be to each other, as 1 :: 1.55 :: 1.92, 1 being the lesser and uniformly ascending grade. This must hold true, unless the engines were permitted to exert their whole power, uniformly as well on the descents, as on the ascents, of the undulating planes, but this could not be allowed, for in practice there are many circumstances, which limit the speed of an engine, both in reference to safety, deterioration of the machinery, and the difficulty of arranging the slides for extreme velocities; or rather of suiting them to the variable velocities, which such a system would render necessary. For these reasons, it has never been considered expedient to calculate upon a velocity, on a descending plane, greater than that which might be permitted upon a level, with safety; and upon such steep planes as 80 feet, not even so great. But in order to compensate for the loss of time in ascending, the velocity required to produce this effect on the descending planes, would be entirely inadmissible; therefore the difference of time in descending by the regulated velocity, and that which would be required to compensate for the loss of time in ascending, would be lost on the undulating line. A very serious objection to this principle of grading, is to be found in this, viz. the route across the summit, in addition to its grade of 40 feet, is necessarily a crooked one, and in order to overcome the total resistance, it is essential that the curves be diminished to the greatest extent practicable. In doing this, we are very often obliged to encounter deep cuts, at the points of the ridges and spurs; and it is at these places that many of the deepest cuts will be found. Applying the undulating principle at these points, and thereby increasing the grades to 80 feet, they might, added to the curves, present a combined resistance, too great, in many cases, for the power of the engine to overcome. In another view, the objection is equally serious. The practical difficulty of working an engine upon such a line would be exceedingly great. To those who have examined the subject, it is known that the engine works to very great disadvantage when the velocity has to be constantly changed; and to work effectively, it is previously regulated for a particular velocity, and the valves arranged accordingly, It is not simply the question of letting into the cylinders a greater or less quantity of steam; but it is in adapting what is technically called the lead, to the velocity which it is designed to travel with. This lead is different in amount for different velocities. A certain velocity is necessary to generate steam; of course this velocity would be attained in the descents; but evidently it would be unsafe to give the engine such a load as might reduce the speed on the ascents below that which would be required to produce steam. To one who has travelled upon roads with steep grades, the truth of this remark must be known-he must have occasionally witnessed the entire stoppage of the train. After giving to the subject the mature consideration which its importance demands, we are fully of the opinion, that nothing has been developed by the recent surveys, which justify us in changing the opinion we expressed in the last Report, and we now respectfully reiterate that we consider the route by Morey summit entitled to your preference, and accordingly recommend that it be adopted. The accompanying Tables (A. and B.) contain a synopsis of routes 13, 14, and 15, referred to in the above Report. They exhibit every detail, necessary for a comparative view of the several routes. The former contains the length, grade, excavation, embankment, cost, &c. of each. The latter contains the length of each curve, with the length of the corresponding radius. WM. GIBBS MCNEILL, GEORGE W. WHISTLER, } ENGINEERS. W. H. SWIFT, RESIDENT ENGINEER. In a number of the first impression the formula at page 31 is erroneously printed, it should be L=1(E+1) g SYNOPSIS OF ROUTES-(Continued.) Sta. Sta. Ft. Ft. From To Rad Cur. From To 15600 300 131001 600 13700116003500 |