As elevated railways of this type are somewhat costly, and a simpler and cheaper form would be a desideratum, a short line across country was built as an experiment at Cologne-Deutz. The stays, measuring from 9·6 feet to 28·5 feet, were made either of wood, or of iron tubes, and met at the top in a cap, from which was jointed the sheet-iron supports that carried the mono-rail. By means of this jointed connection, the strain was always of a central character, and, therefore, more easily borne. At intervals of about 660 feet a couple of stays were firmly braced together, in order to give stability to the overhead structure and to take up the longitudinal thrust. In consequence, even with light locomotives, the traction power was very high, and on the line at Deutz it was found that a locomotive drawing two carriages full of passengers could ascend a gradient of 1 in 6 with perfect safety. But a means of adapting a mono-rail to every condition had some time before been thought out. In 1883-4 Charles Lartigue, the eminent French engineer, developing the principle conceived by the great Telford, constructed some small lines in Tunis and Algeria for carrying esparto grass. The cars were drawn by animals in a special form of mono-rail, the model upon which Mr. F. B. Behr, ASS. INST. C.E.--who modestly disclaims all originality in the matter--has worked for years, greatly improving in practical details the original design, and constructing for the first time mono-rail trains that have been successful in the carriage of both goods and passengers by steam and electricity. [Illustration: FIG. 6. PLAN OF A BEHR MONO-RAILWAY CAR _By permission of Mr. F. B. Behr, Ass. Inst. C.E._] The Lartigue single-rail system, as perfected by Mr. Behr, is as follows, but of necessity my description is a mere outline.