408 



REPORT 1864. 



Preliminary Investigation of the Mechanical Properties of the pro- 

 posed Atlantic Cable. By William Fairbairn, LL.D., ^c, F.R.S. 



It appeared essential to the public interest that the second attempt to sub- 

 merge a telegraphic cable across the Atlantic should not be left to chance, 

 that a close and searching investigation should be entered upon, and that 

 nothing should be left undone that could be accomplished to ensure success. 

 For the satisfactory attainment of this object, it was considered necessary — 



Ist. To determine by direct experiment the mechanical properties of every 



cable submitted for submergence in deep water; 

 2nd. To ascertain the chemical properties of the insulator, and the best 



means to be adopted for the preservation and duration of the cable ; 



and, 

 3rd. To determine the electrical properties and conditions of the cable 



when immersed under pressure at great depths. 



These varied conditions were left to a committee, on whom devolved 

 the consideration of every qxiestion relating to 

 the efficiency and ultimate security of the cable. 

 That of its mechanical properties was left in 

 my hands ; and I was requested to undertake 

 the first division of the inquiry, and to deter- 

 mine, by actual experiment, the strengths, com- 

 binations, forms, and conditions of every cable 

 considered of suitable strength and proportion 

 to cross the Atlantic. To fulfil these condi- 

 tions and ensure correct results, a laborious series 

 of experiments were instituted ; and in order to 

 attain accuracy as regards the resisting powers 

 of each cable to a tensile strain, they were bi'okcn 

 by dead weights suspended from a crab or crane a, 

 by which they could be raised or lowered at 

 pleasure. The weights were laid on one hundred- 

 weight at a time, and the elongations were care- 

 fully taken and recorded in the table as each 

 alternate fourth hundredweight was placed on the 

 scale until the cable was broken. By this process 

 we were enabled to ascertain with great exactitude 

 the amount of elongation in 7 ft. 6 in. — the length 

 between the two iron clips screwed round the 

 cable, near the ends of the loops by which they 

 were suspended, as shown in the annexed figure 

 at a, b. The hook and blocks to which the cables 

 were attached belonged to a travelling crane 

 that elevated or lowered the platform b, contain- 

 ing the weights, to heights corresponding with the 

 stretch as the weights were laid on. Having ad- 

 justed the apparatus, the experiments proceeded 

 in the. order shown in the following Tables, 



In this investigation it will not be necessary 

 to give the experiments in detail, and for the 

 present a summary of results will suffice. 



In the following table will be found the ultimate strength of nearly all 

 the differently manufactured cables of Great Britain, and it will be seen that 



