at the summits of the piers: these plates are firmly bolted together, and also to a strong horizontal plate, the whole forming what is called a saddle. The saddle is not fixed to the pier, but rests on fifty friction rollers, these resting on a thick iron plate, which is supported by a solid mass of iron and timber girders. The pier itself, being pierced with arches, may be considered to consist of four columns of brickwork; the girders, therefore, are so arranged that no weight is thrown on the arches, the whole weight resting on the columns. The saddle is capable of moving eighteen inches each way, equal to three feet entire motion; so that if either span were crowded, the chains would adjust themselves, and the strain be still perpendicular upon the piers, and have no tendency to pull the pier over. The method of putting up the chains was thus:-Two sets of wire ropes, each consisting of three ropes, were hung from abutment to abutment over the piers, in the exact situation the chains were to occupy, these scaffold ropes, as they may be called, being distant from each other equal to the length of the connecting pin. A few feet above the scaffold ropes, two other ropes were hung in like manner; on these traversed two light boxes, very much resembling a carpenter's bench turned topsy-turvy. These cradles, as they are called, were connected together, and contained two windlasses, like those over a common well; these cradles held the workmen. A barge containing the links was moored under the cradles; four men in the cradles hauled up a link; and when they had raised it above the scaffold ropes, the connecting pin was put through, and the pin being allowed to rest on the scaffold ropes, of course supported the link. The cradles were then moved forward, and two links joined to the single link, then one joined to the two; the chain consisting thus, in the first instance, of alternately two and one links. When this two-and-one-link chain was completed, the scaffold ropes were not required, the two-and-onelink chain forming, as it were, a scaffold for the rest of the links; and thus was this bridge erected without any scaffolding but these few ropes, and without the slightest impediment to the navigation, and without a single accident. The cost was Brick work, £63.000, by Mr. Chadwick. Engineer in chief-Sir I. K. Brunel. Resident Engineer-Mr. P. Pritchard Baly. On the Peculiar Features of the Atmospheric System. A paper was read by Mr. Berkeley, which consisted of a series of questions on the "peculiar features of the Atmospheric System," and Glasgow Prac. Mec. and Eng. Mag. had for its object to elicit opinions upon the comparative practical advantages and disadvantages of the atmospheric and locomotive systems. The chief points which were raised consisted of the mechanical difficulties in the application of the atmospheric system to level crossings and sidings, and the performing the work at the stations, &c., which, in spite of the ingenious device of the engineers who had adopted the system, appeared to entail cost and complexity. The advantages and economy of frequent trains on short lines were admitted, but it was stated that the same plan could be practised with locomotives without any disadvantage. For a long line, the benefit of the plan was questioned. It was shown that greater safety did not exist even on single lines, when the circumstances were equal, and the electric telegraph applied to each; in fact, that when the whole position was considered, the balance of advantage of probable freedom from accident, would appear to be somewhat in favor of the locomotive system: that greater speed had not been usually attained, or that if attained it must involve "inordinate cost." The facility for surmounting steeper gradients was questioned, and the inference drawn, that the enormous first cost would confine the application of the atmospheric system to the same narrow limits as were occupied by other stationary systems; and that it must be classed with them only as a means of overcoming lengths of such bad gradients, as did not come within the limits of locomotive power, or where the lines were short and the traffic was great, terminal and simple. In adverting to the cost of maintenance, the comparative advantages of the two systems were examined, and it was argued, that it was fallacious to compare the expense of keeping up the Dalkey line, which was excavated in rock, and resembled "an uncovered stone drain," with that of maintaining the Dublin and Kingstown Railway, which was a sea embankment, stretching across a part of the bay, and on which the trains were not unfrequently stopped by the waves. examination was entered into, of the difficulty of removing the earth from slips, or doing any of the usual quantity of contractor's work on the line, without having recourse to locomotives; on this point, the observation of Mons. Legrand, the French Minister of Public Works, might be quoted. On his return from inspecting the Dalkey Railway, he said that there could not be any doubt of the applicability of the atmospheric system to some positions, and probably with advantage, "mais après tout il fallait avouer ce n'était pas un cheval à la main, comme la machine locomotive." In the discussion which ensued, the theory propounded by Dr. Robinson in his recent examination before the Parliamentary Atmospheric Railway Committee, that “a steady uniform height of barometer had nothing to say to the velocity," or did not indicate, as Mr. Stephenson had stated, in his report, "a maximum uniform velocity," was examined, and it was admitted that the case which he proposed in illustration of his theory, was practically impossible, and was irrelevant to the subject. The supposition of the existence of a perfect vacuum in front of the piston, would throw aside the question of the uniform action of the machinery, with an accelerating motion of the train, which, it was An shown, must produce an unsteady height of the barometer; the condition of a steady height could not exist, unless both the power of the resistance due to the velocity, were either equally irregular or regular; in either case an exact balance being maintained. In Mr. Stephenson's experiments, the circumstances of regular power and steady height of the barometer, were shown to exist simultaneously, and the inevitable inference was that a regular uniform maximum velocity was obtained. Dr. Robinson's case was allowed "to have been stated only for the sake of argument," but a practical inconsistency in Mr. Stephenson's experiments of a steady height of barometer with a slight accelerating velocity, was put forward as condemnatory of his report, on the supposition that it was more practicable to note the velocity than to observe the indication of the barometer, and that the true reason for this slight acceleration, was the shortness of the line, and that hence no accurate result could be arrived at. The question of the loss arising from the evolution of caloric in the air pump, due to the condensation of the air from its rarified condition in the tube to the density of the atmosphere, was considered, and was admitted to be at least as great as had been stated by Mr. Bergin.-Proc. Inst. Civ. Eng. Roman Tunnel at Marseilles. Athenæum. In your number of February 8th, there was a short notice from the French papers of a very curious tunnel, supposed to be of Roman construction, which had recently been discovered under the mouth of the harbor at Marseilles, connecting the two forts of St. Jean and St. Nicholas. I have just returned from Marseilles, and while there made inquiry for the tunnel, and was assured that they had first heard of such a structure from the Paris papers. time, either, that such a report has been spread. some tradition that such a thing does exist, but kind has yet been made. This is not the first There appears to be no discovery of the April 14, 1845. I am, &c., PHILIP N. BROCKEDON. Report of the Engineer in Chief of the Georgia Railroad and Banking Company, to the Stockholders in Convention, May 17th, 1845. Engineer's Department, Geo. R. R. & Banking Co., } TO THE HON. JNO. P. KING, President: Sir-Since the date of my last annual report, our road has been extended to Covington, twenty-six miles west of its former terminus at Madison. During the same period, the graduation and bridging upon the whole line, with some immaterial exceptions, have been completed. The wood work of the superstructure will be laid in a few days, continuously to the Little Stone Mountain, 17 miles above Covington, VOL. X, 3RD SERIES-No. 2.-AUGUST, 1845. 8 and the iron (which has been delayed by the Yellow River Bridge) to a point some six miles beyond the river. To get thus far, we have had to require the iron to be wagoned across the river, at the expense of the bridge contractor. Within a week, however, the bridge will be finished so as to pass the trains, and there will then be no farther interruption to a rapid continuation of the work to its final terminus. The following statement will show the amount expended on account of the extension of the road, up to this date : "Engineering, Depots, Wells, Divis. Houses, &c., 24,259 30 731,851 11 894,000 00 $162,148 89 Which amount will be sufficient to meet all further demands for construction of road, depots, &c., extend the warehouse at Augusta, and supply such additional machinery as may be required for the road this year. Notwithstanding the interruption to the progress of the work, from the magnitude of some of the bridges, and the almost impenetrable character of many of the rock excavations, I have every confidence that the entire road will be ready for use by the time reported to the last annual convention of stockholders. In connection with the Western and Atlantic Railroad, (which will be finished to the Oostenaula about the same time,) we shall then have a continuous line of railway from Augusta, of 250 miles-nearly double the length of our main line in use at the present time. The extension of the Western and Atlantic Railroad beyond the Oostenaula is, for the present, suspended, in consequence of the absorption of the state appropriation upon the road below it. It seems to ine, however, that its early continuation to the Tennessee, appeals to too many of the incentives that control the actions of individuals and communities, to permit a long time to elapse before the work shall be again resumed. Without this extension to the navigable waters of the West, the state cannot expect to receive a remunerating traffic upon her road. With it, she will not only add greatly to the revenues of her work, but elevate its character, from a mere local improvement, to that of a national thoroughfare, connecting the "fertile West" with all the important markets on the Southern Atlantic slope. The completion of the road to Chattanooga, will also place the Tennessee River in the same commanding position, as an avenue of trade between the West and the Southern Atlantic States, that the Ohio now holds to the northern and middle states, and it will present equal claims upon the general government for appropriations, to render it navigable for steamboats at all seasons, which it is understood can be effected at a much less cost than upon the Ohio. The importance of the early completion of the improvements referred to above, to the prosperity of our enterprise, are too well known and appreciated by our stockholders to have required any notice of them in this report. But as public attention has been called to another route, to accomplish the same object, terminating on the Tennessee lower down, which may divide the friends of the work, and, consequently, delay its execution, I have thought it proper to present a few remarks on this subject, which, it appears to me, is so deeply interesting to us, both as citizens of the state and stockholders in our road. While I am inclined to admit, that a route terminating on the Tennessee, at Gunter's landing, would have been preferable as the original design to that at Chattanooga, I am decidedly of the opinion, in view of the small amount necessary to complete the road as now laid out, and the impossibility of raising the capital required to build it on the route proposed, in a satisfactory manner, that it would be both a waste of time and money, to deviate from the present track. In expressing doubts whether the terminus selected for the state road on the Tennessee, at Chattanooga, was the best that could have been obtained, I am not insensible to the many and strong reasons which influenced its choice, and must confess, that even with all the lights now before me, any preference entertained for the Gunter's landing route, would be surrendered, if the navigation of the river between these points should be perfected. The whole of North Alabama and Tennessee would then be accommodated, and by a short branch to Rome, the rich valley of the Coosa would also be drained. The business of the road, and the expenses incurred in working it, during the year ending on the 31st of March, are shown in the following summary statement. A statement in detail of the several accounts below, will be found among the accompanying papers. Extra Trips with passengers, &c., 33,381 77 |
