STUDY OF JAR WIRES. 177 



sufficiently sensitive for measuring the insulating quality 

 of the gutta-percha itself employed and indicating the 

 same in figures. 



When the insulation -resistance of the conducting 

 wires coated with this gutta-percha had then in a 

 similar manner been determined numerically they were 

 faultlessly insulated, provided the measured result 

 agreed with the calculated. If the resistance of the 

 conductor of the complete cable was not greater, and 

 the resistance of the insulator of the same not less, 

 than that ascertained by calculation, the cable might 

 be regarded as faultless. 



It was not to be expected that such exact testings 

 could be carried out by measuring currents. For deter- 

 mining the position of faults, for which I had as early 

 as 1850 found and published the necessary formulae, 

 the inexact current-measurements were also insufficient. 



It was necessary therefore to have recourse to 

 measurements of resistance, but for that there were 

 still wanting good practical methods of measurement, 

 and especially a fixed standard of resistance. Finally 

 the knowledge of the physical properties of the jar 

 wires, as I had termed the underground conductors 

 on account of their property of acting as large Leyden 

 jars, was still too undeveloped for planning long sub- 

 marine lines without risk of failure. 



I had been intently occupied with the study of 

 these questions since 1850. My labours belonged to 

 the time when the great investigator Faraday astonished 



the scientific world with his fundamental discoveries. 



12 



