SCIENTIFIC AND TECHNICAL LABOURS TO 1850. 119 



take place only when all the automatic contact-breakers 

 are again closed, i. e. the armature -movement of all 

 the apparatus inserted in the circuit is completed. 



Manufacture of insulated conductors for subter- 

 ranean or submarine telegraphs by coating wires with 

 gutta-percha. 



Construction of machines, which press the gutta- 

 percha without seam round the wires to be insulated. 



Discovery of the phenomena of the charge in in- 

 sulated subterranean or submarine conductors, and 

 establishment of the law of the charge for open and 

 closed circuits. 



Establishment of the methods, measurements, and 

 formulae for determining the place of faulty conduction 

 and insulation in subterranean circuits. 



The underground wires, both those without external 

 protection and those with an armature of lead, had 

 meanwhile continued to come into use even beyond 

 the confines of Germany; among other states Russia 

 had adopted the system and connected St. Petersburg 

 and Moscow by a subterranean wire. In Prussia how- 

 ever the deterioration, which had occurred in the first 

 lines soon after their construction, continued to make 

 uninterrupted progress. The causes, which contributed 

 to this and finally led to the complete destruction of 

 the lines, have been already mentioned. The almost 

 morbid endeavour, called forth by political exigencies, 



