Comparing the atmospheric with the locomotive system, Mr. Stephenson admits, with light trains upon steep inclines and at considerable velocities, the atmospheric system (in common with all systems in which stationary engines are employed) may possibly exceed the capabilities of locomotive engines; but that if the loads be converted into equivalent loads on a level, then the locomotives have the advantage. Tnu3, taking the experiment No. 4 in the table of the Dalkey performances, (which he considers as indisputably the most favourable one recorded,) the load was 26.5 tons taken up an incline of 1 in 115 at a speed of 34 .7 miles per hour, which he shows to be equivalent to 44 tons upon a level at the same speed of 34.7 miles per hour; but this is much exceeded daily on many lines of railway, and especially by the Great Western, and the Northern and Eastern. On a long series of steep gradients, extending over several miles, and where the nature of the traffic is such that it is essential to avoid intermediate stoppages, the atmospheric system would be most expedient; but if intermediate stoppages are not objectionable, as in the case of the conveyance of heavy goods and mineral trains on the railways in the neighbourhood of Newcastle-upon-Tyne, the application of the rope is preferable to the atmospheric system, as is fully established by the comparison made between the Kingstown and the Euston inclines.

On the questions of expense of construction, and of working a long line of railway, the report is equally unfavourable to the atmospheric system; but upon these points the arguments are necessarily based upon assumptions, as, from the fact of the system not having yet been brought into operation on an extended scale, no reference can be made to experience; and the premises upon which Mr. Stephenson argues are so widely different from those assumed by the advocates of the atmospheric system, that we cannot be surprised at the enormous discrepancy of the conclusions at which they severally arrive.

In computing the cost of construction under the atmospheric system, its supporters always assume that a single line will be sufficient; but this Mr. Stephenson does not admit; on the contrary, he contends that the only means by which the atmospheric system can (if at all) meet the various exigencies of ordinary railway traffic, is to employ a double line of tube: this at once doubles the actual cost of the apparatus, and at the same time disallows those claims to economy of construction, founded upon the smaller quantity of land required, and the diminished size of the bridges and tunnels. We regret that our space will not allow us to give at length the arguments by which Mr. Stephenson supports his opinions, and that we must limit ourselves to his calculations of the comparative cost of the system.

Mr. Samuda, modifying his calculations by his experience on the Dalkey line, gives the following as his estimate of the cost for the apparatus, as applicable to such lines of railway as the London and Birmingham: -

COST PER MILE IN LENGTH.

Vacuum tube 15 inches diameter ...................................................

1,632

Longitudinal valve, etc. ..................................................................

770

Composition for lining, and valve groove .....................................

250

Planing, drilling, etc. ....................................................................

295

Laying, joining, etc. ....................................................................

295

Station valves, and piston apparatus ...........................................

100

3,312

Engine, 100 horse power, with pump, etc. .....................................

4,250

Engine house, chimney, etc. ...........................................................

450

Total for 3 1/2 miles ......................................................................

4,700

Cost per mile in length ..................................................................

1,343

Total cost per mile ....................

4,685

On this Mr. Stephenson remarks, "It will be observed, that Mr. Samuda has only estimated for a single line of vacuum tube, and a single series, under the impression that such an arrangement is adequate to meet every necessity; but from what has been said on this part of the subject, I think it is made evident that such a limitation in the arrangements on any important line of communication would be very inexpedient, to say the least: I have consequently revised this estimate, and the following appears to me to be the minimum expense at which the atmospheric apparatus could be applied to any extensive line of railway:-

COST PER MILE IN LENGTH.

Vacuum tube 15 inches diameter ...................................................

67,000

Two engines, 250 horse power each, at 33,000 lbs, with pumps, etc. complete, at 25 per horse power ....................... ....

12,500

Engine house, Chimney, reservoir or well .......................................

1,500

Total for 3 1/2 miles ........................................................................

14,000

Cost per mile in length ....................................................................

4,000

Total cost per mile ...................

11,000

"This amount exceeds Mr. Samuda's estimate very considerably, but the cause has been sufficiently explained.

"The power of the engines that I have assumed may at first appear large, but taking the engine on the Kingstown and Dalkey railway as our guide, it will be found, that the power reckoned upon does not exceed that which would be required to ensure sufficiently high velocities, with only the average passenger trains which now travel on the London and Birmingham railway; and we must bear in mind that the atmospheric system involves the necessity of employing very nearly the same power with light as with heavy trains.

"The engine at Kingstown may be taken at nearly 200 horse power, and capable of moving a train of about 36 tons, upon a gradient of 16 feet per mile, at 35 miles per hour. If we extend the length of tube to 3 1/2 miles, when the increased leakage is added, the power required to move even such a load (which is below the average load of the London and Birmingham traffic) at this velocity, will be upwards of the 250 horse power, which I have assumed as requisite, and which makes the gross expense 11,000 per mile. *

"By referring to the half yearly statements of accounts of the London and Birmingham railway company, it will be seen that the capital invested in locomotive engines up to 31st December, 1843, was 171,974 17*. 6d. For the purpose of arriving at the whole capital actually invested under the head of power, we must add locomotive engine stations for repairing etc.: this item is not separately stated in the account, but we shall be safe in taking it at 150,000, making the total investment for power, 321,974. It must be understood that I am not attempting here to comprise all the sums which might come under this heading, supposing the accounts to be fully dissected, my only object is to make a comparative estimate, which is done correctly enough without introducing such items as would be common to both systems. The comparison of capital expenditure for power upon this basis on the London and Birmingham railway, would stand thus: -

Locomotive engines and stations ................................................

321,974

Atmospheric apparatus for 111 miles, at 11,000 per mile ...........................................................................................

1,221,000

making a difference in favour of the locomotive system, as far as capital in power is concerned, of 899,026. This large disparity in the cost of the two descriptions of power might, it is urged, be more than saved by a reduction in the original cost of construction of the railway. This is partially true in the case of the London and Birmingham railway, but not by any means to the extent generally imagined.