Page images

making disorderly noises as they rushed tumultuously over the rocks. The sloughs seemed even as that famous one of Despond, encountered by the Pilgrim in his noted progress, thick, deep, and almost endless. The structures, frequently composed of three slender sticks only, intended as guides to conduct across the troubled rivulets, mouldered away by the years of a venerable old age, afa. forded but frail support to the tread. The miles indicated by stakes fairly marked with numerals, went slowly by. Plodding onward, often knee deep in the rich black mould, they were at length passed, and the green fields hailed with a degree of pleasure, those only can duly appreciate, who have traversed the wilderness.

The vegetation is luxuriant in the woods of the North. Plants of medicinal virtue, or of beautiful forms, creep along the earth, or twine about their neighbors, in wreaths of brilliant colors, wasting their sweetness unseen. On the high lands tower up the Maple, Beach, and Birch ;, in the lower regions the Cedar, Fir, and Larch are intermixed.

The face of the country is diversitied by gentle undulations and lofty elevations. Streams intersect the vallies in all directions, and the soil, accumulated by the annual deposits of centuries, is deep and fertile, covered with tall trees and thick shrubs. The dim blue heights, the murmuring rivulets, the silver lakes, and the heavy rolling rivers are grouped together, and at no distant period will present powerful attractions for the hunters of the picturesque and beautiful.

Such is the route, destined, at a future period, to be one of the great inlets of communication from Canada. The distance from Quebec to Hallowell, whence the intercourse with the ocean is free, is about two hundred miles, and from the ancient metropolis of the Provinces to Boston, the mart of the Eastern section of the States, does not now much exceed three hundred and fifty miles, and will hereafter be diminished. It is pleasant to anticipate the period when the splendid hotel will invite the weary to rest and refreshment in the waste places, when the hurrying stage coach and the magnificent equipage, filled with the active men of business or the idle votaries of amusement, will roll along the broad and smooth highway on the solitary hills we have attempted imperfectly to describe, and neat cottages clustering in the cheerful towns, will spread along in the spots where the Beach and the Maple now hold undisturbed possession.

SELECTED. FROM THE JOURNAL OF PHILOSOPHY AND THE ARTS. On the general Nature and Advantages of Wheels and Springs of Carriagesa

the Draft of Cattle, and the Form of Roads. TAKING wheels completely in the abstract; they must be considered as answering different purposes. • First, they transfer the friction which would take place between a sliding body and the comparatively rough, uneven surface over which it slides, to the smooth oiled peripheries of the axis and box, where the absolute quantity of the friction as opposing resistance is also diminished by leverage, in the proportion of the wheel to that of the axis.

Secondly, they procure mechanical advantage for overcoming obstacles in proportion to the square roots of their diameters, when the obstacles are relatively small, by increasing the time in that ratio, during which the wheel ascends : and they pass over small transverse ruts, hollows, or pits, with an absolute advantage of not sinking, proportionate to their diameters, and with a mechanical one as before, proportionate to the square roots of their diameters.

Consequently, wheels thus considered cannot be too large ; in practice, however, they are limited by weight, by expense, and by convenience.

With reference to the preservation of roads, wheels should be made wide, and so constructed as to allow of the whole breadth bearing at once; and every portion in contact with the ground should roll on it without the least dragging or slide; but it is evident from the well known properties of the cycloid, that the above conditions cannot unite, unless the roads are perfectly hard, smooth, and flat; and unless the felloes of the wheels, with their tires, are accurately portions of a.cylinder. These forms, therefore, of roads and of wheels are the models towards wbich they should always approximate.

Roads were heretofore made with a transverse curvature to throw off water, and in that case it seems evident that the peripheries of the wheels should in their transverse sections become tangents to this curve, from whence arose the necessity for dishing wheels, and for bending the axes; which contrivances gave some incidental advantage for turning, for protecting the nave, and by affording room for increased stowage above. But recent experience having proved that the curved form of roads is wholly inade. quate for obtaining the end proposed, since the smallest rut intercepts the lateral flow of the water; and, that the barrel shape confines carriages to the middle of the way, and thereby occasions these very ruts,ấroads are now laid flat, carriages drive indifferently over every part, the wear is uniform, and not even the appearance of a longitudinal furrow is to be seen. It may, therefore, confidently be hoped that wheels approaching to the cylindrical form will soon find their way into general use.

The line of traction is mechanically best disposed when it lies exactly parallel to the direction of motion, and its power is diminished at any inclination of that line in the proportions of the cosine of the angle to radius. When obstacles frequently occur, it had better perhaps receive a small inclination upwards, for the purpose of acting with most advantage when those are to be overcome. But it is probable that different animals exert their strength most advantageously in different directions, and therefore practice alone can determine what precise inclination of this line is best adapted to horses, and what to oxen. These considerations are, however, only applicable to cattle drawing immediately at the carriage ; and the convenience of this draft as connected with the insertion of the line of traction, which continued ought to pass through the axis of the wheels, introduces another limit to their size.

Springs were in all likelihood applied first to carriages, with no other view than to accommodate travellers. They have since been found to answer several important ends.

They convert all percussion into mere increase of pressurethat is, the collision of two hard bodies is changed by the interposilion of one that is elastic, into mere accession of weight. Thus the carriage is preserved from injury, and the materials of the road are not broken : and, in surmounting obstacles, instead of the whole carriage with its load being lifted over, the springs allow the wheels to rise, while the weight suspended upon them is scarcely moved from its horizontal level. So that, if the whole of the weight could be supported on the springs, and all the other parts supposed to be devoid of inertia, while the springs themselves were very long and extremely flexible, this consequence would clearly follow, however much it may wear the appearance of paradox ; that such a carriage may be drawn over a road abounding in small obstacles without agitation, and without any material addition being made to the moving power or draft. It seems, therefore, probable that, under certain modifications of form and material, springs may be applied with advantage to the very heaviest wagons; and consequently, if any fiscal regulations exist either in regard to the public revenue or to local taxation, tending to discourage the use of springs, they should forthwith be removed.'

Although the smoothness of roads and the application of springs are beneficial to all carriages and to all rates of travelling, yet they are eminently so in cases of swift conveyance, since obstacles when springs are not interposed, require an additional force to surmount them beyond the regular draft, equal to the weight of the load multiplied by the sine of the angle intercepted on the periphery of the wheel between the points in contact with the ground and with the obstacle, and therefore proportionate to the square of its height; and a still further force, many times greater than the former when the velocity is considerable, to overcome the inertia, and this increases with the height of the obstacle, and with the rapidity of the motion, both squared. But, when springs are used, this latter part, by far the most important, almost entirely disappears, and their beneficial effects in obviating the injuries of percussion are proportionate also to the velocities squared.

The advantages consequent to the draft from suspending heavy baggage on the springs, were first generally perceived about 40 years since on the introduction of mail coaches; then baskets, and boots were removed, and their contents were heaped on the top of the carriage. The accidental circumstance, however, of the height being thus placed at a considerable elevation, gave occasion to a prejudice, the cause of innumerable accidents, and which has not, up to the present time, entirely lost its influence; yet a moment's consideration must be sufficient to convince any one, that when the body of a carriage is attached to certain given points, no other effect can possibly be produced by raising or by depressing the weights within it, than to create a greater or a less tendency to overturn.

The extensive use of wagons suspended on springs for conveying heavy articles, introduced within these two or three last years, will form an epoch in the history of internal land communication, not much inferior perhaps in importance to that when mail coaches were first adopted, and the extension of vans in so short a time to places the most remote from the metropolis, induces a hope and expectation, that as roads improve, the means of preserving them will improve also, possibly in an equal degree, so that permanence and consequent cheapness, in addition to facility of conveyance, will be distinguished features of the M'Adam system.

FROM THE MECHANIC'S MAGAZINE. RELATIVE EFFECTS OF STEAM AND GUNPOWDER. A SERIES of well conducted and decisive experiments were made by Count Rumford, on the expansive force of fired gunpowder, a detailed account of which, together with engravings of the apparatus employed in so hazardous an undertaking, are to be found in the Philosophical Transactions for 1797 ; of the facts and the truth of the results, no shadow of doubt can exist, and they therefore deserve serious attention.

In these experiments the Count put the small quantity of twelve grains of gunpowder into an iron chamber, of which the bore was a quarter of an inch; weights were placed upon a valve closing the orifice; the powder was fired, and it was found to exert a force of 9431 atmospheres. Seventeen grains, when fired in a similar bore, could not raise a weight of 8081 lbs. placed on a valve which had an area of the twentieth part of a square inch; but eighteen grains raised that weight, and thus exerted a force equal to 10,977 atmospheres, or 165,000 lbs. on each square inch.

In these experiments the powder filled only about half the cavity; hence it expanded to double its bulk, and still exerted this amazing force; but when the whole cavity, equal only to one tenth of a square inch, was filled with twenty six grains of powder (a quantity insufficient to charge a pocket pistol) the solid cylinder of hammered iron was burst asunder, though it was in every part an inch and a quarter thick, or five times the bore; to effect which would require a force equal to 54,750 atmospheres, or 410,624 lbs. on the square inch. This latter result rests upon a calculation of the force requisite to burst an iron cylinder of the given dimensions.

I have examined that calculation, and believe it to be correct; but, whatever doubt may be entertained as to this fact, tliere can be none with regard to the former-for, in them, the power was estimated by the dead weight which the fired gunpowder actually lifted when placed over an orifice of a given size. In these we find a valve, the surface of which is but the twentieth part of a square inch, loaded with nearly four tons, and the elastic force overcomes and lifts it—a fact almost incredible; and, compared with which, the load on the valve of the highest pressure steam generator that ever was invented sinks into absolute insignificance.

It has been stated that from seven hundred to a thousand pounds per square inch is the elasticity of the steam used by Mr. Perkins,

« PreviousContinue »