Something valuable has been furnished and may still be furnished by the falling down of old walls: for when they fall after standing many years, we have, generally, a right to suppose they were almost strong enough, and from their profiles we can easily calculate the force which overturned them, and which they should have been able to withstand.

Ten well-reported cases of this kind would be worth more, probably, than any set of experiments, however elaborate or skilfully conducted.

Such reports should make known, fully:

(1.) The nature of the embankment, the weight of a cubic foot, and the natural slope of earth, as well as can be ascertained.

(2.) The character of the wall, the weight of a cubic foot, and the pulling force necessary to separate a square foot of surface-the force acting at right angles to the joint of separation.

(3.) The nature of the foundation, whether mud, sand, clay, gravel, &c., and whether compressible or incompressible.

(4.) The exact profile of the wall, embankment, and artificial foundations, as first constructed; and, if the rotation was gradual, the change in the direction of the faces prior to the fall.

(5.) The extent of the wall overthrown: and all other particulars calculated to throw light upon the case.

The formula for the thickness of vertical revetments, if the principles advanced in this paper are correct, 'should stand thus:

in which k is the coefficient of stability, and C about one-tenth the pulling force necessary to separate a square unit of surface-otherwise more accurately determined by the means described in Mr. Barlow's work.

Making h = 12 feet; h' = 12 feet; a = 45°; S = 156 lbs. ; s = 125 lbs.; and C 500 lbs. ; that author obtains, a 2'.435; which our formula also gives when we suppose k = 1.38. For k =2, a common value, we have x

= =

2'.933.

It is, doubtless, proper in many cases to take the cohesion of masonry into view. It would not, however, be proper to graduate, in view of any such aid, walls of fortifications liable to be battered by cannon; or walls of any structure exposed to unequal settling and consequent cracks.

In conclusion, it is necessary to remark, in justice to Mr. Barlow, that he himself has pronounced the investigation in question "a very imperfect sketch," and that it has evidently received much less of his attention than many other matters treated of in his book.

A new Method to Project Circles Isometrically.

PROSSER, C. E., New York.

By THOMAS

Fig. 1. Draw the two Isometrical diameters; (i. e. the two equi-conjugate diameters of the ellipse which is to represent the circle,) unite their vertises so as to form a rectangle with its diagonals; circumscribe the whole with a circle passing through each angle of the parellelogram, the sides of which will thus form chords to its segments; with the chord of half the arc of a lesser segment as radius, describe another concentric circle cutting the diagonals of the rectangle, at a, a, a, a.

From each angle of the rectangle as centres, and with its largest side as radius, describe arcs cutting each other within the rectangle as at b, b. From the same centres, and with the diagonal of the rectangle as radius, describe arcs on the opposite side of the figure, as at

c, c.

From each of the points a, a, a, a, as centres, describe arcs passing through the vertises of the isometrical diameters which are on the same side of the conjugate axis, but on the opposite side of the transverse one. From the points b, b, and c c, as centres, describe arcs in continuation.

Note.-b, b are on the transverse axis of the ellipse, and c, c, on a line in continuation of the conjugate axis on either side of it.

On the Comparative Advantages of Atmospheric Railways. The paper by Mr. P. W. Barlow, on the Comparative Advantages of the Atmospheric system of Propulsion on Railways, was the result

of an examination of the system, with a view to determine as to the propriety of adopting it on the Tunbridge Wells Branch of the South Eastern Railway. The author first examined the comparative advantages of the atmospheric system over that of traction by a rope; and then he stated the reasons for supposing it to be inferior to the locomotive system. He premised that on lines similar to the Greenwich. and Blackwall, where the traffic was nearly uniform, and at short intervals, the power used admitted of mathematical computation; but that on railways generally, the power required must be irregular, both as the amount required and the duration of its employment, and that ⚫ therefore a power which was restricted to carrying between certain given points only, and certain intervals, would lead to great inconvenience in practice. It would be inconvenient also to have a power which could not be employed for the ordinary repairs of the road, ballasting, removing slips, conveying building materials, working the coal and lime traffic at sidings, moving goods, trucks, carriages, &c. at the stations, all which was done at present by the locomotives with a great saving of time, and of the expense of men and horses. If locomotives were employed for these purposes only, it must be at a great expense; as the keeping up a small locomotive establishment was very costly, and morcover the gradients and curves of the line must be adapted for working locomotives, and thus do away with one of the great arguments in favor of the atmospheric system. It was contended that the subsidence of embankments which at present constantly occurs without interrupting the usual traffic or being perceived by the passengers, would suffice to rupture the air-pipe or strain it in such a manner that the valve would not close, and thus cause a stoppage of the line. Many other and similar practical objections. were stated against the system; but the main point was in the comparative cost of haulage, when examined with stationary and with the locomotive engines. With the former it was contended, that on lines with unfrequent trains, the small portion of time the power was actually employed, and the number of hours for which the steam must be kept up in order to be always ready, would be so disproportionate as to make the stationary engine system far more expensive than locomotive power. The lines with steep gradients were of course excluded from this position. It was considered also that with the atmospheric system, steep gradients increased the expense of power in the same ratio, as the power must always be exerted in whatever way it was applied. Several experiments were then given to show the great expense of fuel per ton of goods on the atmospheric railway, the results were decidedly in favor of the locomotive. The cost of construction was then examined, and it appeared, that referring to the calculation of the cost of working the London and Birmingham line, to lay down the atmospheric apparatus of a double line with a pipe of the required area, would not be less than 10,000l. per mile, or a total cost of 1,120,000l., the interest of which sum at 5 per cent. would be 56,000l., or 500l. per mile, which sum nearly equalled the average cost of working the line by locomotives, and was greater than on many lines. In fact, that a contract might be entered into for

working a line by locomotive power, for the interest of the sum which would be expended in the establishment of an atmospheric apparatus. -The general results deduced were in accordance with these observations, and it was assumed that the atmospheric system could be most advantageously adopted on short lines, with frequent traffic near large towns, where the absence of noise was important; and that railways on steep inclines in one direction, as at Dalkey, was most favorable to the system. In the discussion which ensued, it was contended that many of the objections urged by Mr. Barlow were not well founded, and that many of the practical difficulties he had advanced, had been overcome by the mechanical arrangements now in progress of execution on the more extensive lines, which were destined to be worked on the atmospheric system. That both sidings and level crossings were practicable; by a very simple contrivance, a selfacting platform could be so arranged as not only to guarantee the pipe from any injury by the traversing of a cart across the line, but that by the action of the vacuum in the main, a barrier could be raised on the passing of a train which would effectually prevent the traversing of any vehicle, and thus avoid the possibility of accidents.That instead of the assumed liability to be thrown off the rails, it was shown that the leading carriage being tied down to the piston, greater security was attained, and that on one occasion the leading carriage on the Dalkey line had started before its time, and had actually traversed the distance at a speed of nearly 70 miles per hour, going round curves 130 to 180 yards radius. That the power stated to have been expended in the conveyance of a given gross load, was assumed at too high a ratio, and the fuel also; and that as to the question of cost by haulage by the adoption of small steam power worked only for pumping water, to be used only at the time of forming the vacuum. for unfrequent or for light trains, a system of propulsion might be established, which would be more economical than that by locomotives under the best management.

Trans. Soc. Arts.-Athenæum.

Vulcanized India Rubber.

At a meeting of the Institution of Civil Engineers, February 4, 1845, Mr. Brockedon exhibited some specimens of his "Vulcanized" India Rubber for diminishing the vibration of railways, by a layer of the material being introduced instead of the patent felt, between the base of the chair and the surface of the sleeper. The preparation was a mixture of caoutchouc and sulphur. Its elasticity was of a surprising character, and was stated to be preserved under intense pressure for a long period. It had been tried on the Great Western with success.

London Athenæum.

AMERICAN PATENTS.

List of American Patents which issued in the month of November, 1844, with Remarks and Exemplifications. By CHARLES M. KELLER, late Examiner of Patents in the U. S. Patent Office.

1. For an improvement in the apparatus for the Treatment of Fractures of Limbs; Livingston Roe, White plains, Westchester coun-ty, New York, November 6.

The improvement in question is applied to the well known frame which is provided with joints and extension bars and screws to adapt it to limbs of various sizes, and to extend and retain the limb in any desired position, and consists of "three troughs or movable splints made of wood and so shaped as to correspond with the half of the leg and heel. The three differ in size only, and may be adapted to legs of all sizes. On the lower or convex side of these troughs or splints, and at about equal distance from the extremities thereof, is fastened a plate of metal with flanches on each side of it, and at such distance from each other as to fit the bar when the splints are placed upon it. And the design of them is to secure the said movable splints when sliding on the bar to which it is secured by a key. The object of the movable splint is to enable the surgeon, by removing one and substituting another, to employ which of them he pleases, according to the size of the leg, &c.; and also to enable the surgeon to adapt and treat with one trough only a greater variety of sizes than can be done with any known apparatus. There are other splints adapted to the outer and inner surfaces of the leg and ancle-these are also of different sizes, and have on the outside leather studs, through which the straps for binding them to the leg, &c. are passed. Another splint is adapted to the under side of the thigh, and made movable and secured to the thigh piece of the frame by means of a screw. And three other splints lined with leather are adapted to the sides and top of the thigh, and secured by straps, &c.

Claim. "I do not claim the mode described of flexing and extending the framework; nor do I claim the mode of extending or shortening the splints as described. But what I do claim, is the combination of the splints (whether adjustable or not) with the hinged bar or framework; said bar being extended and flexed in substantially the manner described, and said splints being independent of the bar, and so constructed as to be readily attached or detached at pleasure, for the purpose herein described; the whole construction being substantially as herein set forth. I have applied the same principles of construction to the upper extremities, the modifications being only in form to suit the shape and motions of the upper limbs."

2. For an improvement in the Straw Cutter; E. Taylor, Rochester, Monroe county, New York, November 6.

The movable knife of this straw cutter is operated by having one