102 REPORT— 1842. 



tal railways and for lines of every degree of acclivity, indicating also the respective 

 corresponding loads, in tons, which may be taken. Thus from a tube of 12 inches 

 diameter, with an 18-inch vacuum, or 9 lbs. pressure per square inch, there is ob- 

 tained an atmospheric power of fully 1000 lbs. ; being equivalent to the average ad- 

 hesive power of a locomotive engine ; and this power, with ever}' deduction for fric- 

 tion and resistance of various kinds (all which were specified and tabulated), will 

 propel 464- tons, or 10 carriages over a horizontal railway ; and 9t tons, or 2 car- 

 riages up an inclined plane of so steep a gradient as 1 in 28. With larger tubes and 

 greater pressure more power could be generated, and of course greater loads pro- 

 pelled. These representations were not based on theory only ; they were the results 

 of the working on a piece of experimental railway for the last two years and up- 

 wards on the West-London line at Wormwood Scrubs, only a few miles from the 

 metropolis. The tube at this place is only nine inches diameter; but there will be 

 a most complete practical demonstration on a larger scale shortly, on the opening of 

 an extension of the Dublin and Kingstown railway to Dalkey, now constructing upon 

 the atmospheric principle ; the tube thereon would be 15 inches diameter, the incli- 

 nation of the railway being about 1 in 110 ; the stationary steam-engine, exhausting- 

 pump, &c. calculated to propel thereon heavily laden passenger-trains at extremely 

 high velocities. 



Reference was made to another peculiarity of this system : — If it were requisite to 

 turn on a lathe with care and scrupulous accuracy the insides of the tubes, the ex- 

 pense would exceed any reasonable limits; but a simple cutter is all that is necessary 

 to pass through the pipes on coming out of the foundry-sand ; they are then placed 

 in a proper receptacle and raised to the temperature of melting tallow ; in that state 

 a mop dipped in tallow is passed through the tubes, followed up by a wooden pis- 

 ton, which spreads the unguent in a complete coating, producing an even interior 

 surface : by frequent passage of the working piston, this tallow lining, or tinning, as 

 it were, becomes perfectly smooth and nearly as*hard as plaster of Paris, and no 

 doubt aids considerably in preventing atmospheric leakage, causing the piston to 

 work, practically speaking, in a tube of tallow, but protected by the iron pipe or 

 casing. 



With regard to the velocity attainable by trains impelled by atmospheric pressure, 

 it may be said to be independent of load or gradient ; in fact it is almost strictly 

 regulated by the proportion between the area of the tube and that of the exhausting- 

 pump ; that is, by the velocity with which the air is withdrawn from the tube by the 

 pump. The exhausting-pump piston will travel at the same speed as the piston of the 

 steam-engine working it, viz. not exceeding three miles an hour ; if the trains are re- 

 quired to run at the rate of thirty miles per hour, then the transverse-sectional area 

 of the air-pump must be made ten times that of the tube, and engine power must be 

 provided accordingly ; and so of other velocities. This is independent of the load ; 

 and gravity being practically an equivalent augmentation of the load to be moved, it 

 is consequently also independent of gradient. The tables exhibited were calculated 

 for various velocities, supposing there was no atmospheric leakage ; this must be 

 provided for, and is computed to require additional engine-power to the extent of 

 six-horse for every mile of pipe ; the chief leakage being at the longitudinal valve, 

 and therefore nearly constant, whatever the diameter of the tube. 



It is evident this is a superior mode of employing stationary power, since 

 there is nothing to be propelled or moved but the carriages, and nearly the full 

 dynamic effect of the force generated is obtained. On the locomotive system, half 

 the load, on the average of all trains, consists of the engine and tender ; and in the old 

 stationary system there is the weight of the rope, with the expense and friction of 

 all the attendant mechanism, which is enormous ; and of this the Blackwall rail- 

 way is a palpable example, although the rope-and-pulley system has probably 

 been thereon carried to the greatest perfection of which it is susceptible. On the 

 atmospheric system, there is substituted for a rope of hemp or wire, a rope of air, 

 which, without weight or friction, transfers a power that may be called inexhaust- 

 ible and boundless ; and there is thus obtained the maximum of useful weight 

 carried with the minimum of resistance to be overcome. 



In pointing out the table containing the several horse-powers of the stationary 

 engines to work air-pumps of different diameters, and to create and sustain the 

 vacuum in tubes of different sizes, an explanation was entered into of the term 



