234 SCIENTIFIC AND TECHNICAL LABOURS TO 1860. 



currents with opposite directions could traverse the 

 same conductor without mutual interference. In an 

 article "On the forwarding of simultaneous messages 

 through one telegraphic conductor"', which I contributed 

 to PoggendorfFs Annalen, I demonstrated the inadmis- 

 sibility of this view, and expounded the theory of 

 electro -chemical duplex telegraphy, but also showed 

 that this method was not capable of practical appli- 

 cation. At the same time I described a method of 

 duplex telegraphy with electro - magnetic apparatus, 

 which completely accomplished the desired result. The 

 same method was also independently discovered by 

 the subsequent chief engineer of our firm . Herr 

 C. Frischen in Hanover. It is known at the present 

 day by the name of i 'Duplex signalling method of 

 Frischen and Siemens" and is still frequently employed. 

 At the close of the above-mentioned article I dealt 

 with the theory of signalling with two apparatus in 

 the same direction along the same wire and with that 

 of simultaneous transmission in the same and in oppo- 

 site direction, described also the current ramifications 

 whereby these problems can be solved. 



In the year 1857 I published in Poggendorff's 

 Annalen a longer article "On electro -static induction 

 and the retardation .of the current in jar- wires", which 

 gives the final result of several years' experiments on 

 the physical properties of underground conductors. 

 In this I took up again and developed further the 

 theory of the electro-static charge of underground con- 

 ductors broached by me as early as 1850. This theory 



