MESSRS. EDITORS—In No. 32 of the present volume of the SCIENTIFIC AMERICAN, you say in your article entitled "Canals and Railroads," that "the wisest policy to pursue, apparently, is to utilize the canals, since we have them, as long as they pay their expenses, allowing them to die out gradually." You also assert in substance that railroads will supersede the Erie Canal, but-surely you have not looked at the revolution its enlargement must produce in transporting the vast products of the West from the great lakes to the city of New York. No railroad can ever compete with it either in cheapness or expedition. The present year this canal is to have six feet of water its whole length, and next year seven feet. This will allow it to be navigated by steam propellers, which will reduce the expense of motive power full two-thirds and time one-half. One hundred thousand barrels of flour and half a million bushels of grain can be taken at Buffalo, and delivered alongside the storehouse or ship in New York in much less time, in better order, and at half the cost that it can be done by railroad. A boat carrying 240 tuns, say 2,400 barrels of flour, or its equivalent in grain, can berunfrom Buffalo to New York in five days, with four men, at a net cost of not exceeding $50, besides a fair allowance for use of boat and the tolls. It would require twenty-fourfreight cars to take this freight—the cargo of a single boat—and when on the cars, look at the multitude of .cartmen and the handling it must undergo to get it on shipboard. The idea is preposterous that the immense produce of the West could be transported from the great lakes to the seaboard without the aid of the enlarged Erie Canal, and further, no railroad can ever compete with it in cheapness or expedition. The propriety of taxing railroads or making them pay the same tolls as are charged on the canal is another matter—one, however, which I deem just under the circumstances—but which will be wholly unnecessary when the Erie Canal shall have been enlarged. I assert that the produce of the West must henceforth be transported on the Erie Canal to tidewater, and that railroads cannot compete with it, and must therefore abandon that branch of their business. It is wise, then, to complete the enlargement in the least possible time, and no section of the Union is more interested in this result than the city of New York—a city whose greatness depends on this canal and whose stupidity has always fought against it—from the days of "Clinton's ditch" to this present time. X. Y. Z. Lockport, N. Y., May, 1858. [We have no selfish ends in view in expressing opinions, pro or con, in relation to the Erie Canal. It has no doubt been of great benefit to the whole country, but when those who advocate its enlargement state that freight can be carried on it cheaper than on railroads, and at the same time advocate the imposition of taxes on railroads for the benefit of this canal, we must say that their statements and conclusions are contradictory, and their logic and sense of justice are very different from ours. Our article referred to was principally aimed at the act of injustice whieh was intended to be perpetrated against our railroads, by the late Legislature, for the benefit of the canals, but our correspondent has taken up the matter in reference to the superiority of the Erie Canal over railroads for transporting freight. He anticipates an improvement in the Use of steam on the canal in place of horses for towing. That, no doubt, will be an improvement, as coming nearer to the principle of railroad operations; but another greater improvement would be the adoption of the railroad on the banks of the canal, for the purpose of towing the boats by locomotives. There are some very general and mistaken notions afloat regarding the capacity and economy of railroads for carrying freight. It is our opinion that a double track railroad, of broad gage, built through the center of New York, and employed for no other purpose than carrying freight could be operated as economically, and could carry freight even cheaper than can now be done on the canal. The Beading Railroad, Pa., carries nearly as much freight per annum as the Erie Canal, and there can be no doubt but a railroad of the character we have named could do the same in New York. Our correspondent states that when the Erie Canal is enlarged, a boat will be able to carry 240 tuns of wheat from Buffalo to New York in five days. A locomotive could do the same work on a railroad in two days, running at the slow rate of ten miles per hour. We have not the least objection to the enlargement, repairing, or anything else being done to the Erie Canal from its own resources, but, in strict justice, neither the public nor railroad companies should be taxed for any such objects.