who are interested that it deserves. There are certainly very plain reasons why this is so. For though study may do much, and men of scientific attainments and inquiring minds, have devoted their time and attention to it, yet the defects in all our public tracts are evident to all, and ruinous in their consequences. But all the speculative opinions upon this subject, that have been put forth, and the numerous experiments that have been made, leave ample space for range. of thought and renewed efforts. In all that we have read, and in all that we have seen, however promising-after suffering numerous disappointments, we now place our reliance upon a simple inquiry"Has it been tested?" We heard and we must acknowledge we were rather sceptic, of a plan different from all others, that has been adopted by the Baltimore and Susquehanna Railway company, in the construction of a section of their road, commencing at the depot. This section was laid according to a plan patented by Mr. Herron, civil engineer, and has been in opperation for upwards of two years. The matter had entirely escaped the memory of the writer, but was brought vividly and in a very interesting manner to his attention, by the following paragraph, which appeared in the Baltimore Patriot of the 23d inst:—

"The improved Railway track.-Two years ago a portion of Railway was constructed near the depot of the Baltimore and Susquehanna rail-road in this city, according to the patent trellis system devised by James Herron, civil engineer; and is now (having withstood the breaking up of two winters' frost) in as perfect order as it was the day it was laid down, although it has not received the slightest repair. It costs less than the old defective system of construction. These facts ought to arrest the attention of all concerned in railroads, and may be verified by reference to Charles Howard, Esq. the enlightened President of the company, who was the first to afford an opportunity of testing the new improvement.

"This short notice was sufficient to excite a desire to become more intimately acquainted with a plan which has given such unqualified satisfaction, after a lapse of time sufficient to detect defects if any existed, and thus I had an opportunity afforded by the reception yesterday, of a neatly printed quarto, entitle a practical decription of Herron's patent trellis railway structure," etc. illustrated by engraved plans, with ample explanations, cost of materials, etc.

"It is my intention, as soon as time will permit, to give a short review of the work, in which I shall endeavor to set forth some of the peculiar claims which Mr. Herron's plans have to the particular consideration of all who are concerned in the construction of railways.

We are happy to learn that this important invention has at last attracted the attention of our government, and is gaining popular favor throughout the community. The inventor, James P. Espy, Esq. well known in this country and in Europe, as the discoverer of the "law of storms," it appears is reaping a richly-deserved harvest for his genius and pesevering enterprise. His apparatus has already been employed for ventilating several of our ships of war, as well as the public buildings at Washington, and answers every desired expectation. It is well adapted to the purpose of ventilating public buildings, ships, kitchens, cellars, cisterns, vats, mines, stables, Also for producing a strong draft in chimneys (and thereby prevent their smoking,) flues to steamboats, locomotives, and a multiplicity of other purposes. It may be described as follows; reference being had to the letters in the above diagram, which represents a vertical section, and a full view of the ventilator attached to a chimney :

etc.

A, denotes a chimney.

B, a sheet-iron pipe, secured upon the top of the chimney.

C, a sheet-iron collar, fitting loosely over the pipe B.

D, a hollow cone, made also of sheet iron into which the collar. C, enters.

E, a vane, to keep the cone pointed to the wind.

F, a spindle, on which the apparatus revolves.

The arrows au, bb, cc, and e, indicate the direction of the currents fo air. Suppose the wind to blow in the directon of the arrowsaa, it will pass along the surface of the cone, from its apex to its base, where it will converge as represented by the arrows bb and cc, and produce a partial vacuum at O, the mouth of the cone, and consequently a strong current of air will rush up the chimney A, in the direction of the arrow e.-Hunt's Merchant's Mag.

(From the Civil Engineer and Architect's Journal.]

MR. VIGNOLES' LECTURES ON CIVIL ENGINEERING, AT THE LONDON

UNIVERSITY COLLEGE.

Second Course-Lecture 1.-Railways.--Mr. Vignoles commenced by saying, that, in pursuance of the order stated in his introductory lecture, he would proceed to investigate the principles upon which railways should be laid out under varying circumstances. In calculating the power (of whatever description it may be) necessary to overcome the resistance of a load to be moved on any railway or road, it may be divided into two parts-viz. that necessary to overcome gravity, and that required to meet friction. The former is, of course, common to, and equal on, all descriptions of roads deviating from the horizontal line, and is in proportion to the sine of the angle of inclination; the latter is regulated by the degree of perfection of the road, and of the vehicles moved upon it, and· includes the resistance of all obstacles to the rolling surface, or periphery of the wheel, in addition to the axle friction due to the load or weight placed upon the carriage. It has been assumed, from experiments and observations, that the average friction upon a railway is 9 lbs. per ton, and that this continues the same at all velocities; but there is reason to believe that the latter part of the assumption must be much qualified. The gravity due to the inclination of the plane being added to, or subtracted from the friction, as the plane rises or falls, the sum, or difference, will give the total amount of power necessary to overcome the resistance of the load. The power necessary to overcome the gravity being expressed by the proportion which the rise of the plane bears to the weight to be raised, (say, for example, a ton,) is found by dividing 2240, the number of pounds in a ton, by the denominator of the fraction which expresses the inclination of the plane; thus, on a plane rising one foot vertically in a horizontal distance of 1000 feet, the fractional expression is and the power (retarding or aiding the load,) will be the thousandth part of a ton, or 21 lb. It is evident that, as we arrive at steeper inclinations, this power will at length become equal to that required to overcome the friction; thus, on an inclination of it will be 22409 lb. per ton, and this being subtracted from the friction, on a railway which is commonly taken at that same amount of 9 lb. per ton, it results that no power is required to move a load down such an inclination, or wherever the gravity and friction are equal, and balance each other. The angle that such an inclination makes is called the angle of repose, but will, of course, vary with the friction, due to various descriptions of roads and vehicles. On steeper inclines than such, not only is no power wanted, but there is a gravitating power due to the descent of the plane, and so strongly does this act in steep inclinations, that it is necessary to put on the break, to retard the veloci ty which it occasions. It is found, however, when a train is allowed to descend a steep plane without retardation, that, owing to the resistance of the air, it will, after acquiring a certain velocity, cease to be further accelerated; many theoretical writers have fallen in

to error, by supposing it dangerous to allow trains to descend inclinations steeper than the angle of repose without applying the break. On railways where there are inclined planes of for several miles together, the trains often commence the descent at the rate of upwards of forty miles an hour, and the speed, instead of being accelerated, has been quickly reduced to little more than the thirty miles an hour, or to such uniform velocity that a railway train will acquire on that inclination, varying a little with the weight of carriages, or the length of the train; such being the case, it is evident that lines of railway for locomotive power, can be safely laid out with inclinations of 1 in 100, and even steeper.

It is of the utmost importance, in laying out a line, to consider power which is proposed to be employed, and the mode of obtaining it; thus, if it be intended to lay out a horseway to carry coal from a collery to a shipping place, the line should be made always to descend, and so regulated, that the number of full wagons that may be sent down be that number which may be taken back empty. But horse-power being extremely limited, recourse is had to steam, and the locomotive steam-engine has been applied to railway travelling, as being better suited to the purpose than animal power. The power of the locomotive engine may be defined, not so much by horse power, or cylinder power, as by boiler power, or capability or rapidly supplying steam to the cylinders, and still more by adhesive power, or the weight insistent on the driving wheels, so as to have purchase, as it were, to drag the load after it, for the wheels will slide, more or less, and, under some circumstances, will merely turn round on the rails, without progressing.Many lines appear to have been laid out under the impression that the locomotive engines would always have to carry a maximum load, and, in accordance with this principle, and to enable them to do so, it was some short time since laid down as an axiom, that no inclination should exceed and that gradients should be constantly uniform through the whole length of the line. Experience has shown, however, that the practical cost of conveyance of ordinary trains over lines greatly varying in their gradients, does not materially differ, the wear, and tear, and fuel, seldom being increased so much as 10 per cent., and the other expenses and contingencies being the same, whatever the gradient of the railway, the difference on the whole expense of working and maintenance becomes very small indeed. In laying out a line, then, the traffic must be considered quite as much in the distribution of it as in the totality; for it is evident that, to accommodate the public, the trains ought to go often, and will, therefore, generally be light; and when we consider the great economy in construction, and the little additional expense incurred in the afterworking, we may conclude that railways may be advantageously laid out with much steeper inclinations than they have in general hitherto been, particularly in the remote districts, where the railway system has not yet been extended. A powerful engine will draw an immense load on a level, whereas it often has not more than twenty tons to draw-consequently, gravity ceases to become an object; and even should the

traffic increase in course of time, it will be better to send frequent and light trains than, in the original construction, to incur heavy cost to graduate the road for heavy trains, which are seldom to be carried. This principle must, of course, be confined within certain limits; thus, lines may be laid out with better gradients, where the traffic is very great, and will justify the expense and inconvenience which might result from an engine having always to go up a steep ascent. Railways in England have cost, on the average, £30,000 per mile, and the first cost of locomotive power does not amount to one-fifteenth of that sum. The interest on the capital is, therefore, very great, while that on the power is small, as is also, comparatively speaking, the daily cost of transit due to the power only. If these proportions were different, the latter being increased, while the larger amount (the interest on the cost of the works) were diminished, the capital sunk in railways might have been reduced fully one-half, with equal satisfaction and benefit to the public, for whose use they were designed, and with greater profit to the shareholders.

Lecture II. Railways-Locomotive Power.-In the last lecture .it had been stated that the adhesive power of the locomotive engine depended upon the weight borne upon the driving wheels. The greatest amount of adhesion of iron upon iron, according to the experiments of the eminent engineer, Mr. George Rennie, as published in the Philosophical Transactions, appears to be about one-sixth or one-seventh of the weight of the insistent load. In the locomotive engine, where the bearing of the wheels is upon smooth surfaces, the adhesion will, of course, be less; and in weather when rime or mist congeals upon the rails, it is very small indeed, sometimes none at all. But in ordinary states of the rails, and of the atmosphere, one-fifteenth may be taken as an average. The vicissitudes to which this power is subject, will often account for the varying rates of railway travelling, and it is only when the resistance of the load is less than the smallest amount of adhesive power which the state of the weather or the rails will admit, that the time of transit of a train over any given distance can be insured. Now, the usual weight bearing upon the driving-wheels of an ordinary locomotive, for passenger traffic, is about seven tons, or 15,680 lb.; one-fifteenth of this will be 1042 lb., or, in round numbers, say 1000 lb., for the average available adhesive power of such an engine for moving a load, and on the amount of this alone will depend the weight which the locomotive engines can draw af ter it. The other principal element which must be taken into account in the locomotive engine-viz. the speed-will depend mainly upon the power of the boiler to generate steam with sufficient rapidity. A boiler may have quite sufficient power to move (at a velocity of three miles an hour) a load of which 1000 lb. shall be the representative, but it must be of a far superior description, and far higher powers, to move the same load at a velocity of thirty miles an hour; and this subject does not appear to have been sufficiently considered, though it is of such paramount importance