We give herewith some illustrations of this railway which has recently excited so much technical interest in Europe and America, and which threatens to revolutionize both the method and velocity of traveling, if only the initial expense of laying the line can be brought within moderate limits.  A short line of railway has been laid in Paris, and we have there examined it, and traveled over the line more than once; so that we can testify to the smoothness and ease of the motion.  Sir Edward Watkin examined the railway recently, and we understand that a line two miles long is to be laid in London, under his auspices.  He seems to think it might be used for the Channel tunnel, being both smokeless and noiseless.  It might also, if it could be laid at a sufficiently low price, be useful for the underground railways in London, of one of which he is chairman.  We are favorably impressed by the experiments we have witnessed; our misgivings are as to the cost.  The railway is the invention of the well known hydraulic engineer, Monsieur Girard, who, as early as 1852, endeavored to replace the ordinary steam traction on railways by hydraulic propulsion, and in 1854 sought to diminish the resistance to the movement of the wagons by removing the wheels, and causing them to slide on broad rails.  In order to test the invention, Mons. Girard demanded, and at the end of 1869 obtained, a concession for a short line from Paris to Argenteuil, starting in front of the Palais de l’Industrie, passing by Le Champ de Courses de Longchamps, and crossing the Seine at Suresnes.  Unfortunately, the war of 1870-71 intervened, during which the works were destroyed and Mons. Girard was killed.  After his death the invention was neglected for some years.  A short time ago, however, one of his former colleagues, Mons. Barre, purchased the plans and drawings of Mons. Girard from his family, and having developed the invention, and taken out new patents, formed a company to work them.  The invention may be divided into two parts, which are distinct, the first relating to the mode of supporting the carriages and the second to their propulsion.  Each carriage is carried by four or six shoes, shown in Figs. 3, 4, and 5; and these shoes slide on a broad, flat rail, 8 in. or 10 in. wide.  The rail and shoe are shown in section in Fig. 1.  The rail is bolted to longitudinal wooden sleepers, and the shoe is held on the rail by four pieces of metal, A, two on each side, which project slightly below the top of the rail.  The bottom of the shoe which is in contact with the rail is grooved or channeled, so as to hold the water and keep a film between each shoe and the rail.  The carriage is supported by vertical rods, which fit one into each shoe, a hole being formed for that purpose; and the point of support being very low, and quite close to the rail, great stability is insured.  It is proposed to make the rail of the form shown in Fig. 2 in future, as this will avoid the plates,