I may observe generally that we have as yet little or no experience of the effect of tunnels on lines of railroad worked by locomotive engines, where there is a large intercourse of passengers. On the Leicester and Swannington railroad, there is a tunnel of about a mile long, on a part of the road which is nearly level; it is ventilated by eight shafts, and I have frequently passed through it with a locomotive engine. Even when shut up in a close carriage the annoyance is very great, and such as would never be tolerated on a line of road having a large intercourse in passengers. This railroad is chiefly used to take coals from some collieries near Swannington, and there is no intercourse in passengers upon it, except of the labouring classes from the adjacent villages: the engines burn coal, and not coke; and they consequently produce smoke, which is more disagreeable than the gases which result from the combustion of coke. This tunnel also is of small calibre. On the Leeds and Selby railroad there is a tunnel, on a part which is nearly level, the length of which is 700 yards, width 22 feet, height 17. It is ventilated by three shafts of about 10 feet diameter and 60 feet high. There is an intercourse of passengers amounting to four hundred per day, upon this road, and, generally speaking, they do not object to go through the tunnel with a locomotive engine. The fuel is coke. (_l_) In order to show the present state of railroad transportation in the United States, and enable our readers to compare it with the opinions and facts adduced by Dr. Lardner, we take the latest accounts from the Charleston and Hamburgh Railroad. The engines drag a train of cars which carry a load of 130 tons, and perform the distance (240 miles) in three days, travelling only by day-light. With these loads they mount planes having inclinations of 37 feet per mile. The same engines are capable of carrying passengers at the rate of 40 miles per hour, and often perform 30, but their average speed is limited by regulation to 20 miles per hour. This railroad is remarkable for being the largest which has yet been constructed, and is besides an object of just pride, in as much as it was commenced at a time, when according to Dr. Lardner, the subject was but imperfectly understood even in Europe, and all its arrangements are due to native talent and skill, unassisted by previous discoveries in Europe.--A. E. INDEX. A. Atmospheric air, elastic force of, 23 Atmospheric pressure rendered available as a mechanic agent by Denis Papin, 48 Atmospheric engine, first conception of by Newcomen, 61. Description of, 63. Advantage of over that of Savery, 69 B. Barometer, the, 21 Barometer gauge, the, 123 Belidor, 133 Birmingham and London railroad, probable advantages to be derived from, 206 Black, Dr., his doctrine of latent heat, 76 Blasco de Garay, his contrivance to propel vessels, 42