Several electric flying-machine ideas found their way on to the patent records. In 1893 a Frenchman registered a design for an air-ship with a cigar-shaped body and electrically-driven propellers. There was, however, more originality in an American idea that the progress of trains on the overhead railway might be assisted by the action of balloons in taking the weight of the cars off the rails. Curiously enough, other original inventors tried to get the opposite effect, by devising magnetic arrangements to increase the adhesion of the wheels to the rails. More plausible forms of super-ingenuity have been exercised in connection with established modes of electric traction. For the conduit system one inventor suggested a kind of reversion to the 'continuous valve' of the old atmospheric railway. The slot of the conduit was closed by a continuous series of springs which would be opened in succession by the plough as it passed along. This arrangement was actually tried on an experimental track in London. Another inventor proposed a novel plan for keeping the conductor in a conduit free from damp. The conductor was to be made hollow, so that hot air could be pumped through it to dry off any accumulated moisture. [Illustration: Fig. 14. The Heilmann electric locomotive--a generating station on wheels. The general arrangement of this locomotive should be compared with that of the modern electric turbo-locomotive described on p. 130 and illustrated in Fig. 15.] The most entertaining freak in connection with the trolley system was a device to enable two lines of car to use a single trolley wire. Cars going in one direction were to carry a double-ended inclined plane which would lift the trolley wheels of passing cars off the wire and let them slip back again. The only drawback to this arrangement was that it would not work. Another inventor who was apparently impressed with the noise of trolley wheels on the wires designed a trolley head fitted with a pneumatic tyre. If he could have persuaded indiarubber to be anything but one of the best of insulators, he would have been completely successful.