Upon the Newcastle and Carlisle railway, where the trains, to accommodate the traffic, travel with less loads, the consumption is about 1 lb. per ton gross, per mile.

Retaining the formula previously laid down, we have the friction and resistance of the Liverpool engines, with a load of 73 tons, =621 lbs. ; the friction of the load and tender, 255 lbs. ; the consumption of coke, 29.3 lbs. 29.3 × R+P = the consumption 876

per mile; consequently,

of coke per mile, according to the experiments. This we find, however, exceeded in practice, owing to the quantity of coke required to raise the steam at starting, waste, &c., in the proportion of 5:9; which would 52.7XR+P

make the theorem,

876

which, we find, does not

materially differ from that formerly given.

M. Pambour gives a different theorem than this, which is, perhaps, more strictly correct; the above, however, is less complicated, and will, we are inclined to think, be found sufficiently correct for general practice.

Art. 8.-Power of Locomotive Engines.

We come now to consider the effective performance of these engines, or the quantity of work they are capable of performing, on given lines of railway.

In the first edition of this work, we stated the performance of the best locomotive engines, at that period in use, as equal to forty tons, conveyed at the rate of six miles an hour; four years after this, or in 1829, according to the table given by Messrs. Walker and Rastrick, they fixed forty-eight tons and a half, conveyed ten miles an hour, as the greatest performance, the directors of the Liverpool railway could expect from them,

and, therefore, at that time little progress had been made in their improvement.

We cannot subscribe to the conclusion of Messrs. Walker and Rastrick, that the same engine, capable only of moving a load of sixty tons, including itself, at the rate of five miles an hour, will propel thirty tons at the rate of ten miles an hour. This is supposing, what is not the case, that the friction of the engine is not greater per ton than the carriages. We have shewn, in Experiment VIII., that the friction of the moving parts of the old engines, when divested of the action of the steam, is equal to 214 lbs., and this was with an engine, the weight of which, including the tender, was nine tons; this is, therefore, the least friction we can calculate upon, being the resistance of the engine without a load. We have previously stated, in respect of the consumption of fuel, that the whole resistance, or that which results when the engine is loaded, should be taken into account. Supposing, however, the resistance of the moving parts only be considered, without reference to the additional resistance, by the pressure of the steam and load, we have the friction of the engine = 200 lbs. If we, now, take the friction of the load at 10 lbs. per ton, or 500 lbs., the whole resistance will be 700 lbs., or 700 × 5=3500, the effect at five miles an hour.

=

Then 3500÷10=350, the resistance which the same power is capable of moving at the rate of ten miles an hour; whence 350 200 150 lbs., the useful effect which the engine is capable of producing, or fifteen tons gross, equal to ten tons of goods.

Our estimate of forty tons, at six miles an hour, would, according to the above calculation, give sixteen tons gross, conveyed at the rate of ten miles an hour.

Supposing, however, Messrs. Walker and Rastrick's standard, to have been at ten miles an hour, and that the proposed engine would take nineteen tons and a half gross, or thirteen tons of goods, at that rate of speed; this would give only six tons and a half gross, or four tons of goods, at the rate of fifteen miles an hour, or at the average rate of travelling upon the Liverpool and Manchester railway at present.

We see, therefore, that in 1825, and for four years afterwards, there did exist some grounds for arriving at the conclusions, which, subsequently to the Liverpool experiments, led to some very satirical remarks, in some of the journals, on the performance assigned in the first edition. As a practical work, it would, especially in that year of excitement, have been very reprehensible to have assigned performances, in anticipations of improvements, which might, or might not, have taken place.

On a reference to that edition, it will be seen, that sufficient stress was laid upon the improvements, of which it was said those engines were susceptible; but it would have been departing from the character of the work, to have assigned performances in anticipation of improvements, that might lead to the adoption of those engines, and which, when adopted, might have been found inadequate to perform the work assigned to them.

We feel the above remarks necessary, in explanation of an error which we have been accused of disseminating, but which, we trust, will have been productive of less injurious consequences than if we had erred in the opposite way.

Apologising for this digression, we shall now endeavour to fix some standard for the present performance

of these engines. In doing so, we, however, feel a difficulty of no ordinary kind. These engines have just, or scarcely yet, perhaps, emerged from a course of improvements, as rapid as they have been astonishing. Little more than eight years ago, we find them incapable of effecting any great rate of speed, four, and, at most, six miles an hour, being their ordinary rates of travelling upon the railways on which they had been introduced; and now we find their regular day's work, with goods, averaging more than twelve miles, and in their daily work with passengers, averaging more than twenty miles an hour, with the utmost ease.

With improvements such as these in progress,-for every engine yet made seems superior to that preceding it, we need scarcely say, that it is extremely difficult to decide upon any fixed standard, without erring on either one side or the other. Perhaps, even before the work issues from the press, their capabilities may be very considerably increased. We are, however, notwithstanding the error into which we are accused of having previously fallen, inclined to fix our data, rather upon their present powers, than upon any speculative capabilities, which, we do not doubt, they may hereafter be made to attain.

We shall, in doing so, be obliged to confine ourselves to the engines on the principle of Messrs. Stephenson and Co.; for, although Messrs. Braithwaite and Erickson, and others, may produce engines, capable of competing with those, in performance, at some time or other, yet, we have, at present, no data, on which we can assign any tangible performance to these engines. We understand, that in an engine, made by Braithwaite and Erickson, for the Liverpool railway, those gentlemen abandoned the principle of forcing the air through the

fire, by means of the bellows, and adopted that of exhaustion, by means of a fan-wheel, applied, in a chamber, at the chimney end of the generator. We have, however, no opportunity of giving correct data of the performance of these engines; and we, therefore, abstain from any opinion whatever as to their merits. An experiment made at Mr. Laird's works, at Liverpool, upon a low-pressure boiler, by an exhausting apparatus, of Messrs. Braithwaite and Erickson's principle, having shewn a surprising result, as to economy of fuel, may induce some to adopt this principle. The length of flues, in this Experiment, (see Note E, Appendix,) was, however, forty-five feet; a length, we should imagine, rather difficult to obtain in a locomotive engine, and to which, we suspect, the economy of fuel in this experiment was attributable.

Both the engines of Messrs. Stephenson and Erickson may, therefore, be said to be on the same principle, viz., that of exhaustion, by mechanical means; the former, by the application of the steam into the chimney, after its passage through the cylinders, and the other by a fan. It remains yet to be ascertained, which, in the first place, produces the most complete exhaustion, and then, which of the two requires the greatest power to effect it; the power required to work the fan, on the one hand, or the loss of power, occasioned by the contraction of the exit pipe, to produce a jet of steam into the chimney, on the other. The principle of exhausting, or producing a current of air for combustion, by mechanical means, allows the whole of the useful heat to be abstracted; none being required to produce a draught in the chimney, as in engines, the process of the combustion of the fuel of which is kept up by the rarefaction of the air in the chimney; and, therefore,