THE ELECTRIC TELEGRAPH. 



stations on the main line can communicate directly with those on 

 the branch line. Sometimes no such connection is provided, and 

 a dispatch from the main line must be repeated at the branch 

 station. This is a defect which ought never to be allowed to remain, 

 inasmuch as simple and efficient commutators may always be 

 provided for connecting the branch and main lines, which in the 

 telegraph play a part similar to the switches by which trains are 

 turned from the main to the branch line, or vice versa. 



It will be evident from what has been said that a dispatch 

 transmitted upon the secondary line of wires may be delivered at 

 the same time at all the stations from terminus to terminus along- 

 the line, or it may be allowed to pass any one or more stations 

 without entering them, by the mere management of the commu- 

 tators provided at the stations severally. 



126. In what has been said, we have adverted to signals pro- 

 duced by the current, without explaining the nature of those 

 signals, or the particular means by which they are produced, 

 because all the circumstances attending their transmission from 

 station to station, which have been explained, are quite indepen- 

 dent of the particular character of the signals, and the way of 

 producing them. We shall hereafter explain the character of the 

 signals which are used, and the instruments by which they are 

 produced. 



From all that has been stated meanwhile, it may be inferred 

 generally that by the commutating apparatus which has been 

 described above, or by any of the endless variety of equivalent 

 contrivances which telegraphic inventors have proposed, any of the 

 following effects may be produced by an agent at any station, at 

 which a current arrives : 1 . Such a current may be made to pass 

 through the alarum, and give notice to the agent of its arrival. 



2. It may be made to pass through the instrument and give signals. 



3. It may be made to pass the station and continue its course 

 along the line withoiit affecting any part of the telegraphic appa- 

 ratus at the station. 4. If it pass through the alarum, or through 

 the instrument, it may be turned into the earth, and so be prevented 

 from going further along the line. 5. If it pass through the 

 alarum or through the instrument, it may after leaving them be 

 directed along the line, so as to continue its course to the other 

 stations below or above that at which it is supposed to arrive. 



127. In some forms of telegraph, the system of signs transmitted 

 to a distant station depends entirely upon the current being alter- 

 nately suspended and transmitted for longer and shorter intervals, 

 and this succession of long and short intervals, variously combined 

 like the notes in music, is converted into a sort of telegraphic 

 language, which by practice is expressed and understood by the 



186 



