180 REPORT — 1865. 



velocity of two miles per hour it would approximate close upon the breaking 

 weight of the cable. 



Assuming, for the sake of calculation, that the strain, including weight and fric- 

 tion, to be t> tons, and as it requires a strain of 7§ tons to break the cable, there is left 

 in reserve If ton to carry the bight of the rope to the surface of the water. Now 

 this is assuming that the cable has been paid out with as much slack as will enable 

 it to be raised in the manner j ust described ; but this is evidently not the case, and 

 as any attempts at raising tbe cable in this form would break it, the slack of 1100 

 yards on each side would require to be taken up, and a drag for 5 miles on each 

 side would be the result, before it could reach the surface. This is evident from 

 the fact that the excess of cable paid out over the distance run was 1210 : 1060, or 

 12J per cent, of slack. This would be equivalent to dragging some miles of cable 

 through the ooze or mud to make up the difference between the catenaries D, E, 

 and AB, AC. 



According to this reasoning, it would appear that any attempt to raise the cable 

 in this way would prove fruitless unless some means were adopted to cut it at the 

 point N on the American side, and haxd in by a second grapnel which would hold 

 fast until the cable was brought to the surface*. 



In the construction of submarine cables, he observed that their success depends 

 on such a variety of circumstances — some of them exceedingly precarious — that 

 the wonder is they have succeeded so well as they have done. In the manufac- 

 ture of a marine cable there is no difficulty with the conducting wire, if made of 

 pure copper ; but the greatest care and caution is required to be taken with the in- 

 sulator to see that the different coats of gutta percha are pure, solid, and free from 

 injury by the abrasion of the external covering when composed of strands of wire, 

 constituting the strength of the cable. 



The following experiments were instituted by the author at the request of the 

 Commission, with a view to determine how far the different kinds of material pro- 

 posed as insulating coverings for electric submarine cables were reliable when 

 placed at the bottom of the ocean under the pressure of the superincumbent water. 



Generally in regard to the insulating powers of the various materials tried, they 

 seem to arrange themselves in the following order of permeability, the first absorb- 

 ing least water, and the last absorbing most : — 



5. Carbonized india-rubber. 



6. Wray's compound. 



1. Chatterton's compound. 



2. Gutta percha. 



3. Masticated india-rubber. 



4. Vulcanized india-rubber. 



7. Unmasticated bottle india- 

 rubber. 



The experiments on the insulating powers of various cores under pressure are 

 less complete than those on absorption, and have been prosecuted under greater 

 difficulties and with less variety of conditions. 



The first experiments have for their object the determination of the increase of 

 weight of various insulating materials when subjected to enormous pressure under 

 water. 



* Since the above was written, the author has been in communication with the engineers 

 and others connected with the Construction and Maintenance Company, who are now con- 

 structing an entirely new cable similar to that of last year, excepting only that the iron 

 wires are galvanized, and the hemp covering is not saturated with tar. This new cable 

 will be attached to the shore ends at Valentia and Newfoundland ; and should this expe- 

 dition be successful, the ' Great Eastern ' and her two consorts will be enabled to return 

 to the spot where last year's cable parted, and by the usual means of grapnels to fish it 

 up, and splice to it as much of the new cable as will carry it forward to Newfoundland. 

 Thus it is confidently expected that two cables will be the important result of this year's 

 undertaking. Considerable difference of opinion appears to exist as to the ultimate success 

 of these critical operations, but as every precaution is taken in having improved machinery 

 for picking up and hauling in, under the direction of Mr. Canning, the Construction and 

 Maintenance Company's Engineer, the prospect of success is much more encouraging than 

 at any former period in the history of this important enterprise. It is moreover intended 

 to employ two more vessels with proper apparatus for grappling the cable at those distinct 

 spots, in order to relieve the strain and to hold by buoys until the cable is cut and hauled 

 on board. 



