Stone bridges so rarely occur upon the roads of America, that they hardly need remark.  The Starucca Viaduct, by Mr. Adams, upon the New York and Erie Railroad, and the viaduct over the Patapsco, near the junction of the Washington branch with the main stem of the Baltimore and Ohio Railroad, show that our engineers are not at all behind those of Europe in this branch of engineering.  From the civil let us pass to the mechanical department of railroad engineering.  This latter embraces all the machinery, both fixed and rolling; locomotives and cars coming under the latter,—­and the shop-machines, lathes, planers, and boring-machines, forging, cutting, punching, rolling, and shearing engines, pumps and pumping-engines for the water-stations, turn-tables, and the like, under the former.  Of this branch, little, except the design and working of the locomotive power, needs to be mentioned as affecting the prosperity of the road.  Machine-shops, engine-houses, and such apparatus, differ but slightly upon different roads; but the form and dimensions of the locomotive engines should depend upon the nature of the traffic, and upon the physical character of the road, and that most intimately, —­so much, indeed, that the adjustment of the grades and curvatures must determine the power, form, and whole construction of the engine.  This is a fact but little appreciated by the managers of our roads; when the engineer has completed the road-bed proper, including the bridging and masonry, he is considered as done with; and as the succeeding superintendent of machinery is not at that time generally appointed, the duty of obtaining the necessary locomotive power devolves upon the president or contractor, or some other person who knows nothing whatever of the requirements of the road; and as he generally goes to some particular friend, perhaps even an associate, he of course takes such a pattern of engine as the latter builds, —­and the consequence is that not one out of fifty of our roads has steam-power in any way adapted to the duty it is called upon to perform.

There is no nicer problem connected with the establishment of a railroad, than, having given the grades, the nature of the traffic, and the fuel to be used, to obtain therefrom by pure mechanical and chemical laws the dimensions complete for the locomotives which shall effect the transport of trains in the most economical manner; and there is no problem that, until quite lately, has been more totally neglected.[3]

Of the whole cost of working a railroad about one third is chargeable to the locomotive department; from which it is plain that the most proper adaptation is well worth the careful attention of the engineer.  Though it is generally considered that the proper person to select the locomotive power can be none other than a practical machinist, and though he would doubtless select the best workmanship, yet, if not acquainted with the general principles of locomotion, and aware