running about 40 miles. It is, therefore, worth one cent per mile run, to cut the wood for this object. To load the tenders, where the business is regular and great, is worth about 20 cents per cord, or a half cent per mile run. The cost of raising the water depends more on the conveniences afforded by the situation. If we assume the average lift at 30 feet, the labor of a man will be equal to raising about 40,000 pounds per diem. Engines usually evaporate from 300 to 400 pounds of water per mile run, which brings the cost of pumping to about the of a day's labor-or about 8 mills per mile run. These items make together 2 cents per mile run.

The result of experience for two roads is given in the following TABLE.

Locomotive Power.-We have now gone over the items in detail which compose the cost of locomotive power, and are, therefore, prepared to sum them up, and compare the aggregate of the averages with the amount at which it is stated in the formula, proposed for the computation of the aggregate annual expenses. These items are

Repairs of engines and tenders per mile run,

Cents.

7.0

9.0

8.0

.9

Sawing wood, loading tenders, and pumping water, per

2.5

Oil for engines and tenders, per mile run,

mile run,

Cost of locomotive power per mile run,

27.4

It will, of course, be recollected that this result is independent of the injury to the road, which we have considered under the usual head of "extraordinary expenses."

The only division of these expenses which is liable to material variation, is the cost of fuel, the price of which varies with the localities. I have already offered an approximate correction of this item, which may be employed for general investigations; and shall shortly take occasion to present a more accurate formula for its computation, based upon a very extensive experience.

It might seem to the general reader, that after presenting the cost of repairs of the road, engines, and cars; the value of fuel and wages of train hands; the consumption of oil, and the injury to the iron, that there would remain but little more to adduce in the premises; but I have yet a very important division of the subject to discuss, which is much too frequently overlooked in investigations of this character.

There are other extraordinary expenses, and certain contingencies which go far to swell the annual charges on every line-without any exception in behalf of the most favorably situated, or of those which are most economically administered.

I proposed, in a former article, to offer an estimate of the probable expenses for the present year, on a railroad in active operation, which is now the object of much attention and interest, in order to exhibit an application of the formula in anticipation of the publication of the company's next report. I take the Philadelphia and Reading Railroad for this purpose; and assume that it will this year give transit to 250,000 tons of freight, and 40,000 passengers. The application of the formula to this work-making proper allowances for its gradients and drawbacks, the facilities for unloading, and having due respect to its age-will produce, for the aggregate expenses, the sum of $265,000. This estimate, of course, refers only to the apparent expenses, and includes no part of those reserved charges-such as the wear of the iron --which are usually denominated "extraordinary expenses," because they are not generally of annual recurrence. The durability of iron rails I assume at about 800,000 tons-while they are estimated by the enthusiastic friends of the road, at 12,500,000 tons, and sometimes at infinity. Where such immense differences exist, time must decide the question. I trust that time may not show that I even am too sanguine, and expect more from the railroad system than it is capable of rendering. (To be continued.)

Mr. Vignoles' Lectures on Civil Engineering, at the London University College.

(Continued from vol. vi, p. 394.)

SECOND COURSE-LECTURE XVII.

Before proceeding to a summary of the second course, Mr. Vignoles observed that there was a material point connected with the subject which had not been sufficiently discussed, viz., the motive power to be employed; on this greatly depended the principles on which a line of railway should be laid out, the end and object being to convey the greatest extent of traffic at the least cost: this cost was compounded, first, of the interest of the capital expended, which should be considered a constant charge; and second, of the periodical working expenses-the work to be done being summed up in the general expression of "overcoming all obstacles to facility of motion." What are these obstacles? They might be divided into two great heads-Gravity and Friction. 1st. Gravity is a natural cause existing under all circumstances, and, affecting lines deviating from the horizontal, in direct proportion to the sine of the angle of inclination. Engineers, therefore, have considered that the first principle of laying out roads, should be (under limits) to approximate as nearly as possible to the horizontal, in order to exclude one of the great causes of obstacle; since, with maximum loads, the retardation arising from gravity is most felt. When such could not be effected, then to dis

tribute the total rise (or effect of gravity) along the easiest ratio of slope. But, in practice, the occurrence of maximum loads, in ordinary passengers and merchandize traffic, forms the exception, instead of constituting the rule, and it is only when a regular and constant heavy trade is to be anticipated, that horizontal communications should be insisted on. 2nd. Friction, is a physical cause, varying according to the perfection of the road, and of the vehicles moving on it. In the practical working of a railway, however, so many expenses arise under the heads of "conducting traffic, management, &c.," common to most lines, whatever the gradient, that they tend to make the cost of overcoming friction, and even gravity, (particularly with the ordinary light loads) but a small fraction of the total charges. Comparing the amount of obstacles on a railway with that on the ordinary road (where the friction, meaning thereby axletree friction, and surface resistance, may be called sixteen to twenty times greater than on a railway,) and assuming the inclination on railway and road to be the same, the general result is that the perfection of the railway surface moved over, and the improvement of carriages, or rather that of their wheels and axles, cause the effect of gravity to be felt in the most sensible degree on railways; while the imperfection of the road causes it to be comparatively scarcely appreciated. Hence with the wretched surfaces of the old roads, and the clumsy wheels of our primitive vehicles, the hills seem to have scarcely added to the obstacles to be overcome. As the road surfaces and carriages improved, and increased speed, and heavier loads were introduced, the necessity for the greater perfection of the ordinary road became apparent, and the remedy was applied in various degrees during the last 100 years until it was completed as far as possible, in the extensive improvements by 'Telford and Macneill on our great highways. But in carrying out this principle on railways we have run into the opposite extreme. We should first take in one sum the retarding causes of gravity and friction, viz., the friction, being constant, or nearly so, putting aside the resistance of the air, at high velocities, vary only in the perfection of the wheel axles, and in the mode of lubricating, (the surface resistance on railways being, practically speaking, nothing,) and the maximum gradient, or rather the gravity due to it: their sum will be the constant divisor for the motive power, of whatever description that motive power might be; and, in considering the latter point, it must be the distribution of the traffic, or what may be called the average hourly load throughout the year, which is to determine the question. In many instances, in this point of view, it would probably often be found most economical to use animal power, (as is done on the Edinburgh and Dalkeith Railway,) were not velocity required-which, on railways, enters so materially into the calculation, that mechanical power in some shape becomes necessary; and this divides itself into stationary power, or when the mechanical means are fixed, and locomotive power, or when the machine travels along with the load. There are two serious difficulties connected with the latter system; first, a great addition to the load, equivalent, on the average, to doubling it; and next, that the fulcrum through

The

which the motive power must be transmitted-that is, the rail on which the locomotive driving wheel impinges-is greatly affected by atmospheric causes, occasioning great variation in the adhesion, and consequent uncertainty from slipping of the wheels, so that, as explained in a former lecture, the load after a locomotive engine is really limited by its adhesive power, and not, as might at first be supposed, either by the cylinder power, or boiler power. Considered abstractedly, stationary power is cheaper, and always would be so if the traffic were certain and regular, with maximum loads and very moderate speed, even with the present obstacles of ropes, sheaves, and all their contingent complicated apparatus; but at high speed, with a great length of rope, the experience of the working of the Blackwall Railway has shown that for passenger trains only, there was, compared with the most expensively worked lines on the locomotive system, to say the least, no economy in the motive power, though other conveniences arising from the peculiar arrangements on that line, were, perhaps, in this special case, more than an equivalent. A most serious obstacle to stationary power, was the necessity of absolutely stopping, and disengaging and refixing the trains at each station, which stations could not be conveniently, and certainly not economically, placed further apart than three, or five miles, for it could readily be proved, than on a continued distance of six or seven miles of railway worked by a rope, the power of the largest engine that could well be erected, would be absorbed in moving the rope only. Professor then went largely into a consideration of applying stationary engines as the motive power in working inclined planes under a variety of circumstances, and recommended to the students to consult the valuable work of Mr. Nicholas Wood on this subject, and indeed on all the details of railway working, of which, particularly in the third edition, there was most of the latest information. In many situations, however, where water power could be obtained, the stationary rope and pulley system might be advantageously introduced. Gravity became the motive power, on what where called self-acting inclined planes; that is, when the gravity of a descending train of laden carriages brought up a train of others empty, or partially laden; or where skeleton wagons, or water tanks on wheels, could be used as artificial counterbalancing weights in either direction alternately; the circumstances under which self-acting inclined planes could be properly introduced were rare. Mr. Vignoles then gave a clear account of various modes of working self-acting inclined planes; among these was described a curious and interesting one near the great limestone quarries in North Staffordshire; another on the St. Helen's and Runcorn Gap Railway, which he had himself put up, and also the planes for the Great Portage Railway, across the Allegheny Mountains, in the United States of America. Stationary power might also be used to a greater extent on the atmospheric system, whereby, to speak metaphorically, a rope of air was substituted for a rope of hemp, or wire, and where no pullies were required, nor any necessary stoppage at the intermediate engines, where only the carriages had to be. moved, and where nearly the whole dynamic force generated was

made available for motive power. This system had already been explained to the class, and practically illustrated on a railway thus worked, and need not be further alluded to. The Professor was preparing for publication a separate lecture "On the Atmospheric Railway System," to be illustrated with plates, and tables, and appendices, in which that interesting subject would be fully gone into, and all the mathematical and philosophical investigations given, with estimates of the cost of such railways under various circumstances of traffic and gradient; fully enabling the value of the principle, as a motive power, to be appreciated. Although modern practice had almost discarded the use of animal power from railways, it might be proper to refer cursorily to it. A horse seems adapted to drag vehicles, from the mode in which he adjusts his muscular action, so as to throw the greatest effect on the line of draft; in making an effort to draw a carriage, the body of the animal is bent forward, throwing upon the latter the part of its weight necessary to overcome the resistance, the muscular force of the legs being employed in keeping up his traction, and moving the body onward; the effort of the animal being resolvable into these two parts, viz., the action on the load, and that required to move itself by. It may be gathered from writers on this subject, that the force a horse is capable of exerting, is that equal to about one-seventh, or one-eighth part of his own weight: or that, on an ascent of one in seven, or one in eight, the exertion required to overcome his own gravity, is a force equal to that he is able to exert on a load on a level plane. Taking the average weight of a horse, and considering that he is capable of occasionally exerting great extra power on the load, still it seems to be satisfactorily ascertained, that nearly seven parts out of eight of the muscular power of a horse is required to drag his own weight forward, leaving, of course, only one part applicable to the load. But the criterion of a horse's power, in practice, is not the occasional effort of which the animal is capable at a dead pull, or for a short period: we must estimate his strength by what he can do daily, and day after day for a long period, and without breaking him down prematurely. If a horse is to travel at the rate of 10 miles an hour, his power of pulling is greatly diminished, and he can work only an hour or so in the day: at two miles an hour he may give out a power of 150 lbs. on the load: at 10 miles he has scarcely 35 lbs. to spare, and at 12 miles an hour, he can seldom be expected to do more than move himself. This was on the average of horses-all beyond were exceptions. Thus, the application of horses to railways, as the motive power, was very limited; and in laying out lines where they are to be used, to full effect, gravity should be arranged to be always with the load, or, at least, not against it; the rate of traveling only 2 or 24 miles per hour, and the traffic uniform. Mr. Vignoles proceeded to an interesting comparison between locomotive and stationary power up inclined planes, taking the inclination of 1 in 50 as a maximum, and showed that when the traffic was small, and the loads consequently comparatively light, and the daily number of trains not great, locomotive engines, as the motive power, (taking into consideration all circumstances of first cost, and working