130 REPORT — 1853. 



the wind was found already to influence the velocity of railway trains. Why should 

 not its resistance be made available in a case of apprehended danger? For example, 

 let shutters or solid doors, of the height of the train itself, be fixed along at intervals, 

 and at a distance of about three or four feet on each side of each railway carriage. 

 Let a rod or a series of rods run along the floor-line of the whole train, by the motion 

 of which the engine-driver might instantaneously cause the whole of these doors or 

 flaps to fly open and remain at a fixed angle immediatelj' that he sees any danger of 

 a collision. Could it be doubted that such a contrivance would materially impede 

 the speed of the moving train, and assist in its retardation ? He suggested, as an 

 additional retarding agent, a large fan of sti-ong wood-work, which might be made 

 to lie folded at the back of each railway carriage, but which, by the contact of an- 

 other rod, might be made to fly open simultaneously with the shutters or flaps before 

 described. 



Another idea which had suggested itself to the author's mind, was the employment 

 of elecfro-magnetism as a retarding agent, making the iron rails themselves the basis 

 of operations. He then proceeded to detail minutely a plan for fitting up in the last 

 carriage of each train an electro-magnetic battery of soft-iron magnets, which mag- 

 nets could be charged or uncharged by the single contact of a piece of connecting 

 wire with a galvanic battery, to be placed in the charge of the engine-driver or his 

 assistant. A downward pressure of several tons might thus be easily gained, which 

 might be brought to bear on the surface of the iron rails, and which would have this 

 additional advantage, that it might be applied either instantaneously, or, by a simple 

 arrangement, magnet by magnet, as desired. And, finallj-, the author concluded by 

 suggesting an improved method of turning off" the steam, so as to drive it through a 

 series of minute jets facing the front of the train, by which he anticipated a small ad- 

 ditional amount of resistance, on the principle of the aeolipile of the ancients, or 

 Barker's hydraulic mill of modern times. 



On an Experimental Apparatus constructed to determine the Efficiency of 

 the Jet Pump ; and a Series of Besidts obtained. By James Thomson, 

 AM., C.E., Belfast. 



Mr. Thomson had last year given, at the Mechanical Section, an account of a very 

 simple machine which he had contrived for the purpose of raising water from beneath 

 the lowest available level of discharge, by means of a supply of other water coming 

 from a higher level. This machine he designated a Jet Pump, because it raised water 

 by the action of a jet. A drawing and an explanation of it, in its original form, are 

 to be found in the Report of the Transactions of the Mechanical Section for last year. 

 The machine is remarkably simple and free from liability to derangement, having no 

 valves, pistons, or other moving mechanisms. It consists indeed only of pipes with an 

 internal jet, and is capable of working properly when left entirely to itself without the 

 care of an attendant. It had at first been intended chiefly for one especial purpose, 

 namely, to empty the pits of his own patent vortex water-wheels, or other submerged 

 turbines, when access to them is required for inspection or repairs. During the 

 progress of the trials, however, which were made of it for this pui'pose, it soon gave 

 indications of being suitable for much more extensive uses, and of being likely to prove, 

 in certain cases, an advantageous machine for draining swampy lands or shallow lakes. 

 The cases of this kind for which its employment was contemplated are those in which 

 the low ground to be drained happens to have, adjacent to its margin, streams or 

 rivers descending from higher ground. With a view to determine its efiiciency and 

 its applicability in any particular cases of this kind, Mr. Thomson had recently con- 

 structed an experimental apparatus in which a Jet pump could be made to act subject 

 to great variations in the ratio of the height of lift to the height of fall ; and which was 

 suited for indicating accurately the quantity of water lifted, and the height of the lift, 

 corresponding to each quantity of water allowed to fall through any given distance 

 within the working range of the appai-atus. The results obtained give higher 

 efiiciencies than had been anticipated previously to the experiments, and remove all 

 doubt as to the quantity of water which can be raised in any ordinary cases of its 

 employment for the drainage of swampy land. They give, in fact, when taken in 

 conjunction with known laws of the flow of fluids through orifices, the means of 

 calculating, with full confidence, the requisite dimensions and proportions of a machine 

 for the performance of a stated amount of work in the raising of water. 



