.S7A 1 n'lI.UAAl SIEMENS, F.R.S. 47 



OUTLINE OF THE PRINCIPLES AND PRACTICE IN- 

 VOLVED IN DEALING WITH THE ELECTRICAL 

 CONDITIONS OF SUBMARINE ELECTRIC TELE- 

 GRAPHS, 



By WERNER and C. W. SIEMENS.* 



THE failures of the more extensive lines of submarine electric 

 telegraphs, which have hitherto been but too frequently experienced, 

 have become manifest almost invariably by a gradual decrease of 

 insulation. In repairing these lines, it has generally been found 

 that the gutta-percha has become disintegrated by the electrolytic 

 action of the currents employed in working the line in places 

 where the thickness of insulating material had been originally con- 

 siderably below the average, owing to some mechanical injury, or, 

 more frequently, owing to a cavity in the material, forced into by 

 the water, or to an eccentric position of the conductor. 



In such places where the insulating covering of gutta-percha 

 has been of uniform and sufficient thickness, no disintegration or 

 partial destruction of the material is observable, even after the line 

 has been worked for many years. The rapidity with which the 

 work of destruction in faulty places proceeds depends entirely upon 

 the intensity and duration of currents employed in working the 

 line. Faults are produced proportionately more rapidly in long 

 lines, owing to the greater resistance of the metallic conductor. 

 Their progress can be retarded in working the lines with feeble and 

 alternating currents, but it cannot be arrested entirely, and it may 

 be laid down as an axiom that " so long as any thin places are 

 allotted to remain in the gutta-percha covering of a submarine con- 

 ductor, so long will their insulation fail by sloiv degrees." 



It is, therefore, a matter of first importance to prevent, if 

 possible, all irregularity in the insulating covering. The material 

 employed should be perfectly homogeneous ; it should be put upon 



* Excerpt Appendix to the Report of the Joint Committee appointed to inquire 

 into the Construction of Submarine Telegraph Cables, London, 1861, pp. 455- 

 458 and 379-382, being a paper read before the British Association for the 

 Advancement of Science in 1860. 



