THE BRENNAN MONO-RAIL SYSTEM. [COMMUNICATED.] rpHE mono-rail system of transport devised by Mr.
Brennan, and illustrated by a working model exhibited at the Royal Society last week, has naturally attracted general attention and given rise to many speculations as to future applications of the system I not merely to railways and tramways, but to road vehicles driven by mechanical power. The model railway-carriage shown was about six feet long and eighteen inches wide; it was capable of carrying a. man weighing a hundred and forty pounds ; its dimensions were approximately one-eighth of those which might be adopted for a full-sized truck, capable of carrying a load of thirty to thirty-five tons. A temporary track had been constructed around the lecture-theatre, on which a single rail was carried, the curves at the corners being of comparatively small radius. Around this track the model carriage was propelled at varying speeds by an electric motor, for which the energy was furnished by storage batteries carried by the vehicle. It ran on four wheels, placed in pairs in" bogie-frames," two wheels at each end of the carriage. In this respect the arrangement was similar in principle to that commonly adopted for long railway carriages of the ordinary pattern to enable them to traverse curves having a small radius in proportion to the length of the carriage ; with double rails the "bogie" has four wheels at each end, two wheels running on each rail. When the Brennan carriage is running on a straight course all four wheels are in one vertical plane, which intersects the floor along the middle of its length. With this arrangement the obvious tendency of the carriage would be to topple over sideways, its centre of gravity being above the rail, and its condition being unstable even in the upright position. It was startling, therefore, to see a model mounted in this fashion standing, upright and at rest, upon a steel-wire rope stretched between vertical supports ; and to observe that when Mr. Brennan placed weights on one side, representing a load of many tons for a full-sized truck, the loaded side of the model actually rose instead of being depressed. Again, when the model was passing round sharp curves at high speed, instead of inclining outwards, as ordinary carriages tend to do, the Brennan truck inclined slightly inwards in apparent disregard of centrifugal force. To an ordinary observer all this seemed mysterious ; but Mr. Brennan furnished the explanation before his demonstration ended. An assistant lifted out of the model carriage and held in one hand the beautiful gyroscopic apparatus by means of which the marvel was accomplished. Two wheels (or dices) capable of very rapid rotation were seen to be mounted in such a way that when the apparatus was in place in the carriage, and it was upright, the discs would revolve in vertical planes, the axes of revolution being horizontal. These gyroscopes were supported on a plane. surface situated at right angles to the rotating discs, the axes of rotation being so mounted that they were free to turn on that plane. The two gyroscopes were connected by gearing in such a manner that tiny angular deflection of one disc was ceminunieated to the other in a reverse direction. Like all efficient pieces of mechanism, this, when explained, was delightfully simple ; but Mr. Brennan indicated that it Lad been reached by long study and repeated experiments. Having regard to his exceptional skill as a mechanician—illustrated, amongst other things, by the remarkable controllable torpedo which bears his name—it may be assumed that the brief statement made by Mr. Brennanrespecting the development of his recent invention means much.
Mr. Brennan based his invention on the well-known principles of gyroscopic action laid down by mathematicians long ago. He gave many simple but convincing illustrations of these principles in the course of his lecture. Every one is familiar with the well-known toy,—in which a heavy-rimmed wheel is made to rotate rapidly about an axis at right angles to its disc. This wheel is capable of maintaining itself in a practically vertical position against the action of gravity, so long as it rotates rapidly, even when it is overhung at some distance from a point or support at the end of ito asis " of rotation; but at the same time the wheel "processes," or swings round its point of support. The fundamental principle on which Mr. Brennan has worked in his latest invention is illustrated by the behaviour of such a toy. His gyroscopic wheels tend to "precesa "; the axes of rotation turning horizontally, when the truck which carries them tends to incline to one side of the other. Reactions are thus produced capable of resisting further inclinations, and the truck is kept practically upright on its single line of wheels. The mechanical devices by which this principle is applied by Mr. Brennan are all his own ; and the association of two rotating discs, mutually influencing each other, makes the system successful.
Mr. Brennan has designed a single-rail carriage a hundred feet long and twenty feet wide, in which the gyroscopic wheels would be three feet six inches in diameter and be rotated at three thousand revolutions per minute. He estimates that when running in vanto each of these wheels would require less than one horse-power to drive it, and one may be sure that his design would minimise frictional and other resistances. He contemplates the possibility of still larger vehicles when the physical conditions of a country are suitable. Electricity has been employed in the model, and it is well adapted for this special purpose. Other means of propelling single-rail vehicles—steam, gas, or oil engines—might be adopted, of course; or power might be transmitted, if desired, from central generating stations, either overhead or along the track. All these matters of detail leave the principle of the Brennan system untouched. It consists essentially of gyroscopically steadied vehicles, running on a single system of wheels which may travel either on a rail or a road surface. Mr. Brennan has worked out its application to road carriages as well as to railway rolling-stook, and before long the system will be practically illustrated. The inventor attaches much importance to its use for military purposes; and it is obvious that the construction of a single. rail temporary track would be much less costly and difficult than the construction and grading of a double-rail track of the ordinarypattern, even when the gauge is narrow. In opening out new countries it may also be found advantageous to adopt a single-rail system, which would cost less for construction and could be made more quickly. Mr. Brennan, as an Australian, dreams of lines on this system crossing the great Southern continent and completing long-desired aysteme of intercommunication.
It is well known that a wide use of single-rail systems has been advocated. That with which the name of Mr. Behr is associated has been practically applied to a limited extent; and Parliament has sanctioned its use between Liverpool and Manchester, although the construction has not been undertaken. Previous mono-rail proposals have favoured an overhead rail carried by suitable supports, with the carriages suspended below. Mr. Brennan claims that his system, with a rail laid on the ground, will be preferable, and that it can be employed on steep gradients and sharp curves, and is favourable to high speeds. Before a decision can he reached on these controversial matters, or commercial success assured with any single-rail system, farther and fullscale experiments are necessary. Much may be learned from the experimental carriage on the Brennan system which the War Office has sanctioned, and it is desirable that the broad results should be published after the trials have been completed. The results of the application of the system to mechanically driven road carriages will also be awaited with interest. It may be assumed that railway and automobile engineers will be ready to avail themselves of the advantages that may be proved to attach to Mr. Brennan's invention. As matters stand, Mr. Brennan has demonstrated the possibility of ensuring stability in vehicles carried on a single line of wheels, and has devised mechanical apparatus suitable for that purpose. Before established methods will give place to the new system much more has to be done, and the balance of advantage must be shown to lie on the side of change.
CIVIL ENGINEER.
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