run completely straight down the centreline of the track, but rather zig-zags slightly across a small distance. This distributes wear across the bow collector's collector plate, and extends the collector's life. Overhead wires also are 'staggered' for pantographs, so systems may replace bow collectors with pantographs on the trams without modifying the overhead. In addition to some vintage tramways, bow collectors are still used in some tram systems in the former Soviet Union, e. g., in Kazan, Minsk, and Dzerzhinsk. Rigid collectors On the Isle of Man, the Snaefell Mountain Railway's implementation is unusual in that the overhead wire is slack and free to hang in a catenary. Hopkinson bow collectors are used, to avoid problems with trolley poles in high winds on the mountainous route – the Snaefell line also uses a Fell rail for braking. Each car has two rigidly vertical bow collectors, with a slack wire above them making contact under its own weight. The collectors are not quite tall enough to make contact with the wire at its suspension points. They are far enough apart, relative to the pole spacing, so that while one is out of contact with the wire the other is mid span and making good contact. The collectors can only be lowered by unbolting them at roof level, whilst the power is off. This inability to isolate them easily hampered fire fighting when car 5 caught fire in 1970. Similar collectors were also used at first on the nearby and slightly earlier Manx Electric Railway. They gave trouble initially with poor contact and so the slack wire system was developed. A tensioned wire usually gave a good contact but broke contact when the collector passed the pole. Slackening the wire and deliberately lifting it up clear of the collector at the poles allowed its weight to give a reliable contact over the other collector, spaced to be at the midpoint between poles. A revised collector was in use within the first few years, by 1900. A small hinged bow frame was placed on top of the fixed uprights, giving a sprung contact. Bow collectors did not last though and were replaced with trolley poles. See also Current collector References Electric rail transport Tram technology it:Archetto tranviario