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EXPOSITION AT VIENNA.
Supposing N arid S to represent the north and south poles of the permanent magnet, it will be easily seen that on the pressure of the right-hand button M 1 at the sending station, the negative current sent through the coil D would develop a north pole at the near extremity of the soft iron core of that helix, which polarity would be communicated to the free end of the needle d. This needle, attracted by the south pole S, and repelled by the pole N of the permanent magnet, would be thrown over to the indication "free,” while the positive current sent over the line through L, thence through L 1 , l 1 , to the coil G 1 , at the receiving station, would develop a south pole at the free end of the needle y 1 , which would be thrown over to N 1 , 7, e, to the indication "free,” as at the sending station.
The pressure of the left-hand button M would, by reversing the direction of the currents, have a contrary effect on both the needles g and d 1 , indicating "occupied.” The same effects would be produced by pressing M, and M], at the other station upon the needles d 1 and g.
Each signal sent from either station sounds the bells T and T 1 , calling attention to the signal.
Suppose a train now to leave the station A for B, no other being-on the line between the two and all the needles beins; therefore at "line free.” The agent at A having covered the train by his out-door signal, presses the button M 1 . The needles d and g 1 being already at "free,” this would simply ring the bells of the two stations without changing the indicators.
The agent at B, thus advised of the coming of a train, acknowledges the signal by pressing his left-hand button . He also rings the sonneries T 1 and T, at the same time throwing over the needles d 1 and g 1 to "occupied.” The needles at both stations thus indicate that one line of rails is occupied, and that at A is a reminder that the outside semaphore should be at "arrest.”
"When the train arrives at B, the agent there presses the button M} and brings back to "free” the two needles d l and g, again ringing the bell T to notify A of the arrival of the train.
If when one train is coming from B to A, another passes A