holders and the citizens, on the favorable aspect of our enterprize, and its obvious beneficial effect on the business and prosperity of our city in particular. I think we may venture to say, that there is not a city south of the Potomac which has, during the unprecedented pressure of the times for the last two years, shown so decided indications of improvement as Savannah; there has been a greater number of buildings erected during that time than for the same period in many years; our population is rapidly increasing, while that of neighboring cities is declining, and our citizens are animated with the brightest hopes of the future.

Savannah, Nov. 7th, 1842.

Letter from Charles Moering, Esq., Engineer, to Messrs. Eastwick

8. Harrison, Locomotive Builders, corner of Twelfth and Willow Street, Philadelphia.

GENTLEMEN:—In complying with your request to give you my opinion about your Locomotive Engines, I feel called upon to state the grounds that make this opinion what it is.

I do this in view of the interests of science, not intending to pass a mere encomium upon the productions of your establishment. Every engineer is, no doubt, conversant with the fact, that the power of a locomotive engine not only depends on the harmonious proportions of boiler and cylinders, and on the clever mechanical arrangement to work the pistons and transfer motion to the driving wheels; but every engineer must be also aware of the importance of another fact, viz: the manner in which this power is made available in order to draw a maximum load, at a maximum speed, on a railroad.

In examining this point, we find that a fulcrum is required to enable the steam power to act upon the weight, or the load to be drawn. This fulcrum in the locomotive engine, is evidently the grip of the driving, wheels on the rails, meaning the friction between both, or adhesion, as it is technically called. Let a locomotive engine be ever so powerful, but take away the aforesaid friction, and the wheels will slip, the engine will draw nothing. This adhesion, derived from the pressure of the weight of the engine, must, therefore, bear a certain proportion to the latter. Its maximum will be obtained by throwing the largest, its minimum by placing the smallest amount of the engine's weight on the driving wheels. The minimum, however, has at no time been a desideratum, as the largest amount of adhesion is required for enabling an engine of a given power to draw a maximum load at a maximum speed.

In the six wheeled American engine, (the true offspring of American mechanical talent, as possessing a fore truck, which affords a most opportune facility for turning curves, there is but one axle to bear the aforesaid proportion of weight; and this axle is the driving

On its position, therefore, depended the amount of weight to be made available for producing friction. As it was found impossi

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ble, as well as improper in practice, to place this single driving axle under the centre of gravity, for the purpose of equilibrating the entire weight of the engine, there remained but two other positions, viz: behind and close before the fire-box.

To illustrate the effect in both cases, let us suppose two engines, A and B, each of 12 tons weight in running order, with cylinders, boilers, and driving wheels of the same dimensions, and performing the same amount of duty, on two roads of exactly the same kind.

In the engine A, with the driving axle behind the fire-box, it was found that only half of its weight was brought into action for the

12 purpose of producing friction, amounting in this case to = 6 tons. In the engine B, with the driving axle before the fire-box, two

2 x 12 thirds were found available for the same purpose, equal to 8 tons. The ratio of adhesion is, therefore, A:B = 6:8, meaning that the engine B possesses a surplus of two tons in its adhesive pow. er, and, consequently, in its capability of drawing loads.

In further examining our subject, another question arises, concern ing the effect of the given ratio of adhesion on the rails. In the en. gine A we have, as mentioned, six tons on the driving axle, and, therefore, three tons on each driving wheel. In the engine B, however, we find eight tons on the driving axle, and, consequently, four tons on each driving wheel. The proportion of weight on the rails is, accordingly, A:B = 3:4.

Supposing these two engines to run at the same speed, s, and assuming the stress by impact upon the rails to be represented approximately by the speed multiplied into the weight imposed upon each driving wheel, then each line of rails would be percussed by A, with Sx3=3 S, and by B, with S x4=4 S.

This gives a ratio of impact A:B=3S:4 S or A:B=3:4; meaning, for the sake of practical illustration, that the engine B will ruin the rails, take them to be thirty eight pounds per yard, after the lapse say of nine years; whilst the engine A will produce the same deterioration only after the space of twelve years, supposing the amount of traffic and other conditions to be the same in both cases.

Although no actual observations of this nature have been made with regard to the rails, yet the average duration of the wrought iron tires on the driving wheels, proves the above proportion not to be an incorrect one. The duration of tires on engines, with the driving axle behind the fire-box, has been found to exceed the duration of those on engines with the driving axle before the fire-box; and taking the latter to be nine months at an average, the duration of the first has been found to amount to from twelve to fourteen months.

Wrought iron rails being manufactured in the same way as tires, it can be but a fair assumption, that the duration of rails will admit of the same proximate scale given in the above proportion of impact.

This brief exposition, backed by the ratio of tractive power, A:B = 6:8, and by the proportion of duration, A:B=3:4, makes it ob

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vious why the diminution of impact in the engine B, possessing a superior power of traction, was found of such great importance, and has thus constantly occupied the attention of the American machinists and engineers. In pursuance of this notion, the eight wheeled engine was started with two driving axles, one before and the other behind the fire-box.

Supposing such an engine C, to weigh twelve tons, in running order, and of the same dimensions as A and B, the weight on the two driving axles was found to be also two-thirds, or eight tons, yet press

8 ing upon the road, on the four points of contact, only with 2 tons.

4. The proportion of adhesion, or tractive power, is, therefore, A:C =6:8, B:C=8:8, A:B:C=6:8:8.

The ratio of impact, or deterioration of the rails, being C:A=2, 3, C: B= 2:4, C:A:B= 2:3:4.

From this we may infer that rails lasting but nine years under the performance of the engine B, and twelve when traveled upon by the engine A, will not meet with their ulterior destruction before eighteen years, when engines of the kind C, are running upon them under the aforementioned suppositions.

can, therefore, but applaud your resolution of building systematically no other engines but those with eight wheels—four driving and four truck wheels. However, I feel myself called upon to impress you with the advantages that must necessarily result when the number of driving wheels can be augmented to six or eight, without losing that beautiful characteristic of the American engine, viz: the free vibrating truck, which in its office of piloting the engine along the track, I think invaluable for the American railroads, with their sharp turns and light superstructure.

An engine, D, with three, and an engine, E, with four driving axles, lending an opportunity to make their whole weight available for adhesion, which then would be that due to the maximum weight of twelve tons, in the given case, would certainly possess the greatest tractive power, and yet injure the road in a much less degree. The proportions of adhesion, or tractive power, would be the following ones, supposing in every case that the engine possesses sufficient power to slip her wheels in pulling against a fixed point, A:B:C:D: E=6:8:8:12:12; and the proportions of impact, or deterioration of the rails, B:A:C:D:E=4:3:2:2:11.

I am aware of all the difficulties attending what I propose, but I feel, nevertheless, confident that “flexible coupling rods, permitting all the axles, with the exception of the main driver, to conform to the radii of curves, are within the pale of practical feasibility. Only on this condition should I think myself justified in preferring engines with a greater number of driving axles than two, were I even inclined to overlook the greater complication that such a mechanical arrangement must require. I reckon simplicity to be one of the cardinal virtues in any mechanical apparatus, and of the most absolute necessity in the locomotive engine.

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