rails of the road. This last principle was also attempted to be carried into execution upon a common road in Pennsylvania, but failed in both cases; yet it is astonishing how near it came to perfect success, and that the very failure did not lead to the discovery of the mechanical principle that has been finally successful, and will probably, before long, introduce a change in the commerce of the world, not less important than that already introduced by the steam engine in its other applications.

That the friction of the wheel upon the rail is considerable, is well known; and when increased to a certain point, must act in such a manner as to cause a carriage to move forward, and even to draw others after it, is not to be doubted. All, then, that remained, was to increase this friction to the desired limit. In the experiments we have mentioned, but one of the wheels being made to revolve, hence but a fourth part of the whole friction was applicable to this object, and but a fourth part of the practicable effect was produced; could the whole of the wheels be made to revolve by the action of the engine, this greatest effort would be applicable, and this has since been effected by a very simple and ingenious contrivance. By this method, the whole friction of the wheels upon the railway is made to act in the manner of a fixed resistance or prop; and as the friction of iron upon iron, in motion, is one twentyfifth part of the pressure, the effect is the same as if the engine upon its carriages were attached to a revolving chain by a bolt capable of bearing that portion of its weight; if the resistance were to exceed the direct pressure of such a weight, the bolt would break; and for a similar reason, when the wheels revolve upon the rails, no progressive motion would be produced when the resistance exceeded that proportion of the load. But this friction of one twenty-fifth part of the pressure, is not that which opposes the progressive motion of a carriage upon a railway; it is much less in consequence of two circumstances: (1) the physical advantage gained by the rubbing body rolling, instead of sliding upon the plane; and, (2) the mechanical advantage obtained by the action of the wheel as a lever, where the power is applied at the circumference of the wheel, and the resistance at the circumference of the axle.

In the carriages usually employed upon railways, the effective resistance opposed by friction upon a horizontal plane, is found by experiment to be diminished in consequence of the action of these two causes, to one two-hundredth part of the load, or one-eighth part of the friction of the wheel upon the rail. It might hence be inferred, that but one-seventh part of

the whole power is consumed in propelling an engine mounted on wheels with a given velocity, and that it may draw after it, without a diminution of speed, wagons bearing seven times its whole weight, including boiler, water, and carriage; and this has been found to be actually the case in practice.

When the power of an engine exceeds, in however small a degree, the force necessary to set such a train of carriages in motion, the excess will act as an accelerating force, and the velocity of the carriages would continually increase, if the power of the engine could be kept up to its primitive intensity, until the number of strokes performed by its piston reached a maximum. But it is impossible to keep the engine, whose velocity is thus increasing, at a uniform intensity of action; for an increased velocity of the piston demands an increased supply of steam of equal pressure, and as the boiler cannot furnish this, the pressure must diminish, until the excess of power or accelerating force will be zero, at which time the wagons attain their maximum of speed, and the whole system assumes that state, which, by writers on mechanics, is called dynamical equilibrium. The velocity at which this will occur in practice, will depend on the original power of the engine, and the excess of its locomotive power over the friction. Taking all circumstances into account, it is not probable that it will ever be expedient to increase the velocity to more than twelve or fourteen miles per hour; but as this is five times as great as the velocity at which the maximum effort is produced upon a canal, while the load is fully one third of what would be drawn by an equal power through the water, it is evident, that the moment that circumstances will admit the application of the power of steam, railways must be preferred to canals, and in many cases supersede them altogether. The principal of these circumstances is the possibility of procuring a supply of fuel, on such terms as will reduce the cost of the power to a level with animal labour. Hence, when the chief article of transportation is coal, little hesitation need be felt in adopting the railway, with locomotive engines, in preference to any other mode of conveyance.

So also, wherever the number of travellers is great, and the goods to be transported of such value as to render the freight a small object, when compared with certainty, rapidity, and safety, it is to be presumed that rail-ways must be a valuable and lucrative investment of capital. We have in a previous part of this paper, spoken of the materials of which rail-ways are constructed; and we there mentioned that cast iron had superseded wood in Great Britain; wrought iron has also been advantageously introduced in some late erections in that coun

try. We are, however, disposed to think, that in most parts of the United States, wood will be found preferable to either. Under this impression, we have seen with great pleasure, a model constructed by Mr. Fleming, an intelligent civil engineer, who has been domiciliated among us, of a wooden railway; its most valuable feature is its adaptation to small changes of level in the ground, which is attained by elevating every part of it above the surface, except in cases where deep cuts become necessary. A rail-way of this description, if roofed in, like the better kind of wooden bridges, would be very durable, and cost far less than one of cast iron.

Among the modifications of the rail-way that have been proposed in England, is one by Palmer, composed of a single rail, which embodies a similar principal of elevation above the mean surface. We do not, however, mention this with a view of praising it, as we conceive that in every respect the, double wheel track laid with edged rails is preferable, except in the cost of original erection; but to state, that it if have any merit, it may be claimed as having first occurred to an American, Col. Sergeant, of Boston, having invented and proposed a similar kind several years previous to Mr. Palmer. We hope, however, that no national feeling may interpose to lead to the adoption of this plan in preference to others, whose real merits are much greater.

The author of the work before us is an engineer, much distinguished for his science, and for the numerous valuable works of which he is the author. The treatise under consideration, is of all others that we have seen on the subject, the best manual for those who may be called upon to direct the execution of works of the kind. There are others among the great number that have issued from the British press on this subject, that embody matter more interesting to the general and superficial reader, but none that contain any thing like the amount of information that can be usefully applied in forming plans and estimates for new works. The calculations of the strength of rails, the demonstration of their proper figure, and the interesting experiments, and most valuable deductions in relation to the friction of wheel carriages, are new and important additions to the science of the engineer. Should wood be employed in this country, our engineers will find in another treatise of the same author, that will probably become the subject of a subsequent article in this work, all the necessary additional information, founded upon a series of accurate and well contrived experiments, principally made by the author himself. This, work is perhaps, the first of a similar character that has appeared in an

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American dress. . It is an experiment, therefore, in the book trade, and, we hope, will be attended with such success as to induce the enterprising publishers to give us more of a similar character, or even to apply to some competent person to give the American public a full treatise on civil engineering, compiled from the best foreign sources, and containing every valuable addition that has grown out of the practice of our own country. Such a work would be of extreme value; the greatest difficulty our engineers have to struggle with, is the want of knowledge of the practice of Europe, and of the scientific principles of the works they are employed to superintend. The errors committed in road making have been mentioned. We have been more successful in canals, if we take our own state as the instance, but in other directions many failures have occurred that are forgotten in the brilliancy of that important enterprise. Even the canals of New-York are not completed, and competent judges do not hesitate to declare that much remains to be done before they can compete, in correctness and solidity of execution, with those of Europe, however they may exceed in extent any work accomplished within so short a time, and at so small a cost.

LECTURE INTRODUCTORY TO A COURSE OF LECTURES ON APPLIED MECHANICS, DELIVERED AT THE NEW-YORK ATHENEUM, IN THE WINTER OF THE YEARS 1824-25, BY JAMES RENWICK, PROFESSOR OF CHEMISTRY AND EXPERIMENTAL PHILOSOPHY

IN COLUMBIA COLLEGE, NEW-YORK. (Concluded.)

But it is not with these countries that we have any immediate concern; we have derived from them (at least directly) none of our knowledge-and among them, from the neglect of science, the arts are becoming daily less and less perfect. The nations that more naturally excite an interest in our minds, are those of whom a knowledge has reached us through the traditions and histories of the Greeks, and the more authentic and remote, but less circumstantial details, that exist in the sacred records of the Hebrews. These traditions, histories, and records, carry us back to the period when a portion of the human race spread themselves over the plains of Shinar, the mountains and glens of Palestine, and the islands and peninsulas of Greece and Italy, in the state of shepherds, or wandering hunters. In these modes of life, arts are speedily forgotten; when their increasing numbers compelled them to till the ground, and the strong hand of mighty hunters forced them to congregate in cities, their condition must at first have been wretched.

The inhabitant of Babylon, the glory of the world, or of Thebes, with its hundred gates, were devoid of innumerable articles that our meanest citizen considers as absolutely essential. If favourable climates, and even azure skies, rendered them less dependent than we are upon the mechanic arts, still they were deprived of many articles that would have contributed to their comfort, and having no intercourse with foreign nations, were compelled to rely upon their own productions for all that either supports or embellishes life; their luxuries, their comforts, and their conveniences, were restricted within a narrow compass; constantly occupied in labouring for the mere support of a miserable existence, the great mass of the people possessed neither power nor influence, and were the abject slaves of their rulers. While enormous tumuli attest the existence of Babylon-while pyramid, obelisk, and sphinx, indicate the power of the orders of Egypt-no vestige has come down to us of private habitations; they have long since returned to the earth whence their materials were derived. Yet, while we look in vain in these countries for any trace of the buildings that sheltered the mass of the nations, or even for any public works destined to promote the general health, or to improve the state of commerce, we still find either strong indications, or the almost perfect remains, of many great and wonderful structures. These have sometimes been considered as an evidence of high progress in the applied sciences; but more mature reason would induce us to believe them rather the product of mere brute force, applied under the direction of despotic governments, by which the time and even the life of the subject were considered as of no value, than the result of enlightened art. Such was the power and wealth of the ruler, such the abject condition and poverty of the ruled, in those remote times, that any number of men, even to the population of entire nations, might be easily commanded; at the present day, on the contrary, such is the value of labour, such the improvements in the circumstances of the people, as to prevent governments from either executing as stupendous works, or assembling as enormous armies, as they formerly did. The secret of the mighty buildings of the ancients, lies neither in the skill of the artist, nor the application of the aid derived from science-but in the despotic power of the ruler, and the abject submission of the populace. As may be expected from such a state of society, laste in the arrangement of the parts, grace and beauty of form, are wanting in the monuments of Egyptian art; but they are marked by a severe grandeur of shape, and by the minute and VOL. II.

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