A bow collector is one of the three main devices used on tramcars to transfer electric current from the wires above to the tram below. While once very common in continental Europe, it was replaced by the pantograph or the trolley pole, itself often later replaced by the pantograph. Origins When the bow collector was first conceived by German inventor Ernst Werner von Siemens in the late 1880s, American inventor Frank J. Sprague of Virginia had just patented his trolley pole system of current collection from an overhead wire. To avoid contravening this patent, the Siemens company was forced to design its own, unique form of current collection, namely the bow collector. The bow collector was first used by the Siemens electric company in its early electric tramcars in either the late 1880s or early 1890s. The Hobart electric tramway system - the first of its kind in the Southern Hemisphere, opened in 1893 - used Siemens cars with very early bow collectors. Many other continental European and some British tramway systems, including Leeds and Glasgow, also used this method. Construction The bow collector is one of the simplest and most reliable methods of current collection used on tramways. The very earliest versions were simply very heavy-gauge wire or steel bars bent into a rectangular shape and mounted long-side-down on the tramcar roof. The collector was then raised by a spring, so that its top edge would press against the wire above. That top edge is made of a 1-inch (or more) wide steel rod, machined to have a bow-shaped cross section; that cross-section inspired the name. This bow-shaped rod is referred to as the 'collector plate', and in later models may be up to several inches wide, positive polarity are collected by the bow while the other polarity are at the rails, these are for safety purposes. Unlike many trolley poles, the bow collector does not normally have a revolving base (an exception was in Rome, where the entire assembly could be revolved), but is rather fixed centrally to the tramcar's roof. After 1900, the simple framing methods mentioned above were gradually replaced by more complex and sophisticated methods, but the general mode of operation remained the same. The changes of design are most noticeable on systems where both double- and single-deck cars were used on the same system. Single deck trams usually have tall and lightly constructed collectors