But a still greater evaporating power than this is found among the large en gines working on the Great Western Rail way. In an experiment made by Dr. Lardner with the " North Star," drawing 1101 tons gross, at 301 miles an hour, the evaporation was 200 cubic feet an hour.
On the evaporating power of the en gines, other things being the same, must ultimately depend the speed of railway traffic. For it mutt be apparent that no modification which can be made in the mechanism of the engine, no change in the magnitude of the driving-wheels, nor any other expedient of the same kind, can add any thing to the real working power of the machine. Mechanism is the means by which power is modified and conveyed to the working points, not the agent by which it is produced. The real and the only source of power in the steam-engine is to be found in the phenomena which are evolved in the conversion of water into vapor (for an account of which phe nomena see SrnA31); and therefore the limit of railway speed must always depend on the rate at which the locomotive boiler is capable of evaporating water. The ex periments above explained show the ac tual evaporating powers possessed by the boilers now in use, and every addition to such evaporating power will produce a cor responding, though not a proportionate, augmentation of the speed of railway trains.
Nothing can be more absurdly exag gerated than the accounts which have been put in circulation of the speed at tained on railways. No reliance whatever can or ought to be placed on such reports, unless they are attested by competent persons accustomed to that kind of in quiry, and who have been themselves witnesses of them. In the extensive courses of experiments which, for several years back, have been conducted by Dr. Lardner, he has never in any instance, even with an unloaded engine, exceeded a speed of 45 miles an hour ; nor was that speed ever maintained for any considera ble distance. With the best and most powerful engines on the Great Western Railway at their disposal, Mr. Nicholas Wood and Dr. Lardner were unable to attain a spied in their experiments ex ceeding 45 miles an hour. The question, however, of most interest to the publio is, not the speed which can be obtained in experiments for short distances, with engines put into racing order, but the average speed which can be maintained in the general working of a road. The
returns of the railway companies, so far as they have, been made public, do not supply the means of determining this ; but it is known that the first class trains between London and Birmingham, a dis tance of 112 miles, could not until within the last few years make the journey, under ordinary circumstances, in less than 51 hours; this would give an average speed, including stoppages, of 20 miles an hour. On the Grand Junction line between Li verpool and Birmingham, the journey, in cluding stoppages, was usually made in 91 hours, and the distance is 97 miles ; this again is at the rate of about 20 miles an hour.
The quickest journey on record was made August 26, 1848, on the Great Western Railway, England, by the " Cou rier" locomotive, which ran with an ex press train weighing 60 tons, from Did cot to Paddi gton, a distance of 58 miles, in 49 minutes 13 seconds, or at the rate of 67 miles an hour. The average• speed on railways, in this country, varies from 25 to 33 miles per hour.
A new engine has been placed upon the Boston & Worcester Railroad, manu factured by Mr. Ross Winans, of Balti more, which has some peculiarities about it. It is made for burning anthracite coal, and has a fire-box 6 feet in length, 31 in width, and about 2 feet in depth, which will contain at least a ton of coal. The fire grate is composed of stout, se parate bars, so arranged as to permit the firemen to tarn them and shake out the ashes, even when the doors of the fire box are closed.
It is 28 tons weight, with two driving wheels, 7 feet in diameter, and 8 sup porting or truck-wheels—the driving wheels being in the centre. It is made so that the adhesive power or weight may be thrown upon the driving-wheels, for the purpose of ascending steep grades, and thus adhesive power can be concen trated or spread over the whole of the wheels, according as it is needed. We understand that for a short distance it attained the speed of 60 miles per hour.