4 THE SCIENTIFIC PAPERS OF 



adjustable spiral spring. The current is therefore broken and 

 restored by the apparatus itself. The same operation takes place 

 simultaneously in both or all the instruments included in the cir- 

 cuit, and no movement can take place in any unless the current is 

 restored in all of them. By depressing one of the keys before 

 mentioned, an arm, which is fastened to the cogged wheels is 

 arrested, and consequently the movements of all the instruments 

 must cease, their hands pointing, in all of them, to the same letter 

 on the dial plate. 



Each instrument contains an alarum, the construction of which 

 is founded on the same principles as the telegraph. 



When the telegraph is in repose the coils of the alarum instru- 

 ment form, with the earth and line wire, one closed circuit. 

 Before a message can be delivered the arm of every commutator 

 must be turned, whereby the sender of the message excludes his 

 own alarum work from the current but includes his battery and 

 telegraph. His own battery then rings the bell at the other 

 stations, whilst the telegraph at his own station remains inactive, 

 because the alarum work is so arranged that it works with greater 

 facility than the telegraph itself. The receiver of the message on 

 hearing the alarum bell turns the arm of his commutator also, 

 whereby his alarum work is excluded from the circuit, but his 

 telegraph and battery are included in it, and the telegraphs begin 

 to work. 



Mr. C. "W. SIEMENS, the brother of the inventor, attended and 

 explained the working and peculiarity of the invention. 



The thanks of the meeting were given to Mr. Siemens for his 

 communication. 



MR. C. W. SIEMENS * read a paper on an Improved Electric 

 Telegraph, the invention of his brother, Mr. E. "W. Siemens of 

 Berlin, at the meeting of May 30th. The paper was illustrated 

 by a series of diagrams, and a pair of the instruments were 

 exhibited at work. 



Without reference to figures, it is impossible to describe satis- 



* Extract from Notes of Proceedings of the Society of Arts, Session XCV., 1849. 



