448
EXPOSITION AT VIENNA.
that case, however, inspection of the points, which is necessary from time to time in order to keep the connections perfect, would be more difficult.
The use of the foregoing or similar apparatus is the cause of that constant ringing of bell-signals which is so often noticed by the traveller in Europe while his train is waiting at a station. On the single-track routes of the Compagnie du Midi , in France, the discs were almost constantly in position of arrest. Hence, to avoid the incessant rinofinjj of the bell, a simple method was devised by which the action of the apparatus might be suspended by hand at the station and reestablished at pleasure.
On the above line and also on the line of the Compagnie de Lyon a further modification of the apparatus was introduced. Signals at night being given by means of lights, it was thought necessary to keep the stations advised as to the condition of the light, which might by accidont become extinguished, For this purpose a bent rod of steel s (see Plate Y.) was placed near the flame of the lamp, and in Plate v. its upper end was in
serted a piece of copper. The lower arm of the rod was con- nected by a wire to the sonnerie and battery g at the station. The heat of the lamp causes both metals to dilate, but the copper dilating more than the steel, lifts the rod from the point of contact^, which is connected by a wire with the ground. On the extinction of the lamp the metals, it is said, in the course of fifteen or twenty seconds resume their natural dimensions. The lower arm of the rod falls on the point p, the circuit is established and the bell at the station rings. This apparatus is the invention of Mi Boucher. Similar contrivances, the inventions of Messrs. Whitaker, Lewis, and others, with the thermometer attachments, have been patented in England. In the Italian department of the Exposition, near the model of the Mont Cenis Tunnel, is an apparatus employed by the Alta Italia Railway for showing to a station the position of anoutlying switch, which, although equally simple, is on a somewhat different principle from the foregoing systems.
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