By a comparison of the returns published by Dr. Lardner, in his work already quoted, with the more recent results which we have already given, it will appear that within the last two years not less than 3,700 miles of railway have been opened for traffic in the United States. Among these are included several of the most important lines, among which are more especially to be noticed the great artery of railway communication extending across the State of New York to the shores of Lake Erie, the longest line which any single company has yet constructed in the United States, its length being 467 miles. The total cost of this line, including the working stock, has been 4,500,000_l._ sterling, being at the average rate of 9,642_l._ per mile--a rate of expense about 50 per cent. above the average cost of American railways taken collectively. This is explained by the fact that the line itself is one constructed for a large traffic between New York and the interior, and therefore built to meet a heavy traffic. Although it is but just opened, its average receipts have amounted to 11,000_l._ per week, which have given a net profit of 6-1/2 per cent. on the capital, the working expenses being taken at 50 per cent. of the gross receipts. One of the great lines in a forward state, and likely to be opened by the close of the present year, connects New York with Albany, following the valley of the Hudson. It will no doubt create surprise, considering the immense facility of water transport afforded by this river, that a railway should be constructed on its bank, but it must be remembered that for a considerable interval during the winter the navigation of the Hudson is suspended from the frost. A great line of railway, which will intersect the States from south to north, connecting the port of Mobile on the Gulf of Mexico with Lake Michigan and the lead mines of Galena on the Upper Mississippi, is also in progress of construction, large grants of land being conceded to the company by the Federal Government. This line will probably be opened in 1854. It is difficult to obtain authentic reports from which the movement of the traffic on the American railways can be ascertained with precision. Dr. Lardner, however, obtained the necessary statistical data relating to nearly 1,200 miles of railway in the States of New England and New York, from which he was enabled to collect all the circumstances attending the working of these lines, the principal of which are collected in the following table:-- Tabular analysis of the average daily movement of the traffic on 28 of the principal railways in the States of New England and New York.