normal speed." A regular movement free from variation may be obtained by fitting to the upper surface of it a wooden cup filled with mercury, as shown in Fig. 62. The effect of this weight is not merely an increase in the inertia of the whole wheel, but by the oscillations of the mercury greater regularity is ensured. Electro-magnetic Gyroscope.-M. Trouvé has very ingeniously applied his annular motor to Foucault's gyroscope, with the object of maintaining its movement long enough to show clearly the rotation of the earth. The revolving sphere is formed of eight straight electro-magnets joined by their bases to a common cylinder. This wheel is then filled in with a mass of insulating material, and covered by electrolytic action with a deposit of copper. When accurately adjusted on its axis, and the poles of the electro-magnets bared, it is fitted inside the electromagnetic ring, which is suspended from a cross-beam and supplied with a commutator. The sphere thus rotates in a vertical plane, and being revolved for a considerable time, cannot, owing to the rotation, alter its relative position in space; but the beam will have moved through a certain angle from the movement of the earth, and this angle will show the distance the earth has revolved in the time. Great accuracy and precision are of course necessary in such instruments, and this has been obtained in the two constructed by M. Trouvé, one of which was presented by him to the South Kensington Museum. The contacts had, of course, in such an apparatus, to be specially designed to allow of the movement of the support, and not of the revolving parts; and M. Trouvé constructed a very ingenious arrangement of platinum contacts dipping into mercury, which answered the purpose very thoroughly. It might have been feared that the magnetism of the earth would have a prejudicial effect on the accuracy of the instrument, but, owing to the exterior poles of the electro-magnets being all of the same name, and acting on the iron hoop simultaneously at each end of the diameter, there was no north and south line, and the apparatus was always in a perfect state of equilibrium as regards the terrestrial magnetism. CHAPTER V. ELECTRO-CHEMICAL MOTORS. THE idea of applying the expansive force of explosive gas to drive an engine is an old one. Huyghens, it will be remembered, thought to utilise gunpowder for this purpose, and in this case the engine would have been arranged almost in the same manner as in the early attempts at steam-engines. It was in perfecting Huyghens's idea that Papin was led to the discovery of the steam-engine. However, the dangers that might have resulted from the employment of such an explosive power for a long time hindered the development of these motors, in which, besides, the igniting arrangements had never been satisfactorily managed. When the heating effects of electricity became known, several inventors again took up Huyghens's idea, employing as an explosive compound not powder, but hydrogen gas mixed with atmospheric air or oxygen, and by igniting it with the electric spark, or with currents sufficiently powerful to make a wire red-hot. Thirty years ago the papers made a great noise about a machine of this kind, invented by Dr. Carrosio, of Genoa, and in 1852 some papers described an electro-chemical motor of M. Moeff, which appeared to have been L well designed, and is said to have given very good results. However, it was only in 1860 that this description of motor was brought into practical shape by Lenoir, and for a long time it was employed very advantageously in certain industries. It was only when the Otto gas-engines made their appearance that it was abandoned, because it was not so economical. However, as faithful historians, we must describe this engine, which for some time was so well known. It is shown in Fig. 63, and Figs. 64 and 65 give details of the mechanism. The general appearance of the engine is that of a horizontal steam-engine. The cylinder is placed horizontally on a cast-iron bed-plate fixed to a brick foundation, and the piston-rod works between two guide plates. On the shaft is fitted a fly-wheel and driving-pulley. The piston and slide-valves alone are of peculiar arrangement, on account of the electric element. Watt's centrifugal governor is used, and the heavy and cumbrous generator necessary in steam-engines is dispensed with. The gas, mixed with air in the proportion of eight or ten to a hundred, reaches the cylinder by the tube E (Fig. 63), and the distributing reservoirs RR (Figs. 64 and 65), which are opened at the proper moment by slide-valves worked by the eccentric seen in the cut. Two conductors for the production of the electric spark inside the cylinder, consisting of simple platinum wires fixed in insulating blocks, are shown at I and I' at the two interior extremities of the cylinder, and are in connection with the |
