I 1 2 THE SCIENTIFIC PAPERS OF 



units, and the reason of their occurring in such enormous numbers ; 

 but owing to the length of the discussion, he would confine him- 

 self to some of the practical points, on which he wished to make a 

 few observations. Both india-rubber and gutta-percha could be 

 put upon the wire in such a perfect manner that, provided those 

 materials were not tampered with by solvents or excessive heat, 

 permanent insulation could be insured, which was, in the case of 

 i^utta-percha, materially improved by great hydrostatic pressure at 

 the bottom of the sea ; therefore it was chiefly to the outer 

 covering and to the laying of cables, that attention should be 

 directed in order to find out where improvements could be made. 

 He would lay stress upon one important fact with regard to deep, 

 as well as to shallow-water cables, namely, that a cable would only 

 remain electrically in good condition, so long as the outer covering 

 remained intact. He did not believe that a cable could be laid 

 safely without some kind of outer sheathing. The accidents 

 which had occurred to the last Atlantic cable showed how 

 necessary it was to have an outer sheathing which could not be 

 pierced by pointed wires ; but in adopting an outer sheathing, it 

 ought to be a permanent one. It was maintained, in answer to this 

 assertion, that when a cable was laid in deep water, it would 

 probably last for years after the outer covering had decayed. But 

 it was known practically, that cables had failed after the outer 

 covering was gone. In the Red Sea the cable failed, and the 

 Malta-Alexandria cable broke down, wherever oxidation had been 

 most active, through the exposure of the iron wire sheathing. But 

 it had been asked, what forces were there to destroy a cable laid 

 upon a smooth bottom ? If the bottom could be supposed per- 

 fectly smooth and oozy, and if the cable was supposed to have sunk 

 into the ooze equally throughout, then he could indeed find no 

 reason for its failure after the iron had decayed. But was it 

 reasonable to suppose the existence of such a bottom ? Would it 

 not be probable that a dead fish, or the bone even of a dead fish, 

 falling on this soft bottom, would support the cable falling over it, 

 which would be for part of its weight, suspended at that point. 

 The part most exposed at the point of suspension would be first 

 attacked by the corrosive action of the salt water, and it was in- 

 deed a fact, that the iron wires of cables corroded away in points 

 before the whole was materially affected. 



