TRANSACTIONS OF THE SECTIONS. 101 



worked out the suggestion of Medhurst to practical utility, in a way at once simple, 

 efficient and capable of enduring the rough usage necessarily attendant on constant 

 and rapid motion. 



Reference was then made to certain of the drawings and sections representing, 

 drawn to the full size, an atmospheric apparatus equivalent in power to an ordinary 

 locomotive engine, but occupying much less space. It is described to be a cast- 

 iron pipe or tube of twelve inches in diameter, laid, in lengths like water-pipes, be- 

 tween the railway bars, and attached to the same cross-sleepers which support 

 them ; on the upper part of this tube is a narrow longitudinal slot or opening, 

 covered by a valve, the peculiar mode of opening and closing down and sealing 

 whereof constitutes the ingenuity of the contrivance. The valve is a simple flap 

 of leather, one edge of which is fastened down, so as to act as a hinge ; the upper 

 surface of the leather being plated in successive links with flat bar-iron, and the 

 under surface also plated, but with links of a segmental form, to complete the inner 

 periphery of the tube when the valve is closed down. In the tube moves a piston, 

 made air-tight by one or more leather collars ; at the end of the rod of this piston 

 is a counterweight, to keep the rod parallel to the axis of the tube : a connection is 

 made (by one or more plates of boiler-iron of sufficient size and strength, and called 

 the coulter,) between the piston-rod and the perch of a leading carriage or guiding 

 truck, in front of the train moving on the railway. In practice, the piston being in 

 the tube, and at some little distance in advance of the opening of the valve, through 

 which the coulter passes, a vacuum, more or less perfect, is made in that part of the 

 tube in front of the piston by an air-exhausting-pump worked by a steam-engine or 

 other stationary power ; the' air enters by the open valve, and presses at once and 

 directly at the back of the piston ; the opening through which the coulter passes is 

 raised only for a few feet-length at a time, and the valve is rapidly closed down again, 

 as the piston, carrying forward with it the train, moves on ; and being closed, the 

 edge of the valve-opening is hermetically sealed up, and the tube rendered air-tight 

 by a composition of bees'-wax and tallow, varied in certain proportions, according to 

 season and climate : this composition is laid at the valve-edge, in a groove, into which 

 it is pressed by a copper slide, kept just warm by heated charcoal in an attached box. 

 The whole of the mechanical arrangements of rollers, heater, &c. are very far from 

 being complicated, not liable to get out of order, and easily adjusted when deranged ; 

 the operation being completely effected when the carriages travel at exceedingly 

 high velocities, as has been repeatedly done, leaving the tube ready to be again ex- 

 hausted of its air, and allow the next following train to be impelled by the atmo- 

 spheric pressure. In familiar illustration of the principle on which the piston-rod in 

 the tube connects through the valve with the carriage outside, the movement of an 

 ordinary pencil sliding in its case was referred to. 



One leading characteristic of this new system is that of substituting stationary 

 for locomotive power, and in this substitution the advantages will in many cases 

 be great. Even the old system of stationary power, connected with all the obstacles 

 of ropes, sheaves, &c, has still its supporters, both where passenger as well as mi- 

 neral traffic have to be carried on : but with the numerous economies which might 

 be combined in the atmospheric system, the stationary engine, with steam or water 

 as a prime mover to work the exhausting-pump, may once more take the field 

 against the locomotive. This stationary power is to be erected at long intervals on 

 the line of railway, and may certainly be placed at three or four miles, and pro- 

 bably at five, or even six or seven miles apart, working the exhausting-pump, which 

 will be connected by branches with the main tube lying between the rails. 



The air being drawn out by the pump, a certain amount of vacuum is produced 

 in front of the piston, creating a corresponding pressure on the opposite side of it, 

 being about half a lb. on every square inch of surface acted on by the atmosphere, for 

 every inch rise of the barometer. In the ordinary practical working of the apparatus, 

 the usual amount of vacuum obtained may be taken at that corresponding to 16 to 

 18 inches of mercury, or 8 lbs. to 9 lbs. per'square inch ; and experiments have fully 

 proved that the whole, or very nearly so indeed, of the pressure due to the degree of 

 exhaustion is obtained. 



The measure of the power for producing motion is the product of the transverse 

 sectional area of the tube in square inches, multiplied by the number of lbs. pressure 

 due to the vacuum ; various tables of these powers were exhibited, both for horizon- 



