Table B. - Loss Of Power With Different Weights Of Train

wasteful application of power which high velocities inevitably en til. We have in the experiment No. 4, the effective application of a power of 150 horses, of which 78 horse power, or upwards of 50 per cent., is absorbed by the resistance of the atmosphere at a velocity of about 35 miles per hour.

We would call the reader's attention to the power absorbed in obtaining a vacuum, as ascertained by a comparison of column 8 with column 9, and set forth in column 10. Mr. Stephenson observes, "It may not be at first clearly understood why the power of this column (8) exceeds so greatly that given in the next (9), which is the actual power required to work the air pump; but this will be apparent when it is remembered, that the positive power has been here increased in the proportion of the total time the air pump was at work to the time required for the train to pass over the entire distance at its maximum velocity, which increase has been made in order that a direct comparison may be instituted between this total power and the power required for each of the various resistances of the train." We think this point has not been sufficiently kept in view when the power required in the atmospheric railway has been in question, and that, if not a fatal, it is at least a formidable objection to the atmospheric system under any arrangement, and that it goes far to neutralize one advantage claimed for the system, - that the dead weight of the engine and tender is got rid of.

To illustrate this, let it be supposed that the vacuum in the main is produced, not by a pump worked by a stationary engine, but by a travelling piston in the tube, connected to a locomotive engine, the train being connected to another piston detached from the former; and that the distance between the pistons at starting is equal to the length of a section of the tube - say 2 miles: then, if the resistance of the train be equivalent to a pressure of 15 inches of mercury on the area of the piston, or, in other words, if the air in the tube be rarefied to half the density of the atmospheric, it is clear that the locomotive piston must travel two miles before the train begins to move; and if we suppose the engine to be pro\ided with means of cutting off the steam, so as always to proportion it exactly to the resistance, still the power employed in producing the vacuum requisite to set the train in motion will be nearly that required to propel the train half the length of the section, or to propel half the load of the train the whole length of the section.

If the resistance of the train required the air in the tube to be rarefied to one fourth of the density of the atmosphere, equal to a pressure of 22 1/2 inches of mercury, the locomotive would haveto travel over six miles ere the train would begin to move, and the power thus expended would be equal to that required for propelling the entire train three-fourths of the length of the section, or to propelling three-fourths of the train the entire length of the section: in other words, the effect is the same as if an addition had been made to the dead weight of the train, equal in the first supposed case to half, and in the second to three-fourths of the weight of the train. Now, by referring to the table it will be seen that the 18th train, weighing 59.8 tons, required a vacuum in the tube equal to 23 .6 inches of mercury; the power lost, therefore, in this case, will be equivalent to an addition of a dead weight to the train of more than three-fourths of the whole weight, or more than 45 tons. But the weight of the largest engine with its tender on the Great Western railway we believe does not exceed 26 tons, and it is stated that one of these engines would take 156 tons of gross load at 45 miles per hour; in this instance, therefore, the dead weight of the locomotive is only about five-ninths of that of the atmospheric, and constitutes only one-sixth of the gross load; whereas, on the atmospheric line, it is equal to three-sevenths of the gross load.

In the above calculation no account has been taken of leakage, which would of course increase the amount of power lost.

Having given the results obtained on the Dalkey line, Mr. Stephenson proceeds to draw a comparison between the working of the Atmospheric and the other systems. As an example of fixed engines with ropea, he selects the incline on the Birmingham line, between Camden Town and Euston Square, because it presents a case which is similar to that at Kingstown; or, at all events, the disparities are not such as will materially interfere with the comparison. The following table exhibits the results of experiments upon this incline, with the calculations founded thereon; observing that the friction of the several trains is taken (as on the Dalkey line) at 10 lbs per ton, added to the gravity due to the average gradient.

Table Of Experiments At The Camden Town Station

Constants

Average gradient 1 in 106: length worked by rope .91 miles; weight of rope 7 tons; area of both cylinders 2904 square inches; velocity of pistons 224 feet per minute; mean pressure on piston 2 .9lbs and 3 .0 lbs per square inch; friction of engine 13 H. P.; friction and gravity of rope 45 H. P.; velocity of train 20 miles per hour; friction and gravity of train 31 .1 lbs per ton of train.

Mr. Stephenson then compares the fourth train in the last table with the eighteenth train in the preceding table, being two cases which present the closest analogy in the amount of their resistances and velocity. The loss of power from working the rope, as shown in the table, is 30 per cent of the whole; but this must be increased in the proportion of the mean to the maximum velocity, which in this instance is ascertained, from experiments made, to add thirty-seven horse power to the loss, making the total loss by the rope on the Euston incline 45 per cent. whilst on the Dalkey line the loss by the atmospheric apparatus is 74 per cent. This result is obtained with what may be regarded as an average train on the Euston incline; it is evident therefore that in this particular instance the rope is considerably more economical than the Atmospheric system. Assuming other weights of train, as the weight of the train is diminished the proportionate loss by the atmospheric decreases, and the loss by the rope augments; whilst by increasing the weight of the trains the proportionate loss by the atmospheric is augmented, and that by the rope is diminished.