CABLE-TESTINGS FOR THE ENGLISH GOVERNMENT. 205 



control of the preparation and the testing of cables, 

 which it contemplated laying, to our London firm. In 

 these testings for the first time a consistent rational 

 system was adopted, which afforded assurance that 

 the completed cable was faultless, if the conductivity 

 of the copper conductor and the resistance of the in- 

 sulating covering entirely corresponded to the specific 

 resistances of the materials employed. The result was 

 that the insulation of these new cables was more than 

 ten times as great as had been the case in previous 

 submarine cables. 



My brother William and I communicated in July 

 1860 to the British Association the substance of the 

 report delivered to the English Government on the 

 performance of these testings and the methods and 

 formulae employed in a paper read by William, entitled 

 "Outline of the principles and practice involved in 

 testing the electrical conditions of submarine cables", 

 and in this way we made our experiences public 

 property. 



Since then no cables with defective insulation 

 have been laid, and their durability has proved satis- 

 factory wherever mischief has not been wrought by 

 local causes or external violence. In cables laid in 

 shallow water - - both in the Mediterranean and also 

 in the Black Sea - - such a destructive agency presented 

 itself in the shape of a small beetle belonging to a 

 group particularly dangerous to wooden ships (Xylo- 

 phaga). In the cables without iron sheathing laid by the 

 firm of Newall & Co. in the eastern part of the Medi- 



