412 



REPORT — 1864. 



From a long series of well-conducted experiments, it has been found that 

 a good quality of ductile iron improves in strength by elongation, that is, the 

 whole of its fibres are brought into action by the elongation of those first 

 subjected to strain, or, in other words, they yield up only part of their strength 

 until the force reaches the other parts, so as to produce uniformity of action 

 throughout the whole section of the wire. This is a property of good iron 

 which requires to be extended to the manufacture of both steel and homo- 

 geneous wire ; and taking the experiments as they exist in the foregoing series 

 of results, I find that with proper care in the selection of the material in the 

 first instance, a judicious system of manipulation in the second, and a rigid 

 system of inspection and check upon the quidity as delivered, from time to 

 time, during the manufacture, that wii'c of homogeneous iron, -095 inch 

 diameter, can be made of strength sufficient to sustain from 900 to 1000 



lbs. with an elongation of -0068 or —i^ — per unit of length. This description 

 of iron appears to be the most suitable for the Atlantic cable, as it combines 

 strength with ductility, and may be produced at a comparatively moderate 

 cost. Great care is, however, required to maintain, during the whole process 

 of manufacture, the full standard adopted at starting, both as regards the 

 strength and ductility of the wire. 



It was, also, found desii-able to test the separate strands of each cable, as 

 well as the wires themselves. For this purpose a number of strands similar 

 to those employed in the manufacture of the diflerent cables were procured, 

 and the tensile breaking-strain and elongations carefully observed and re- 

 corded. In order to ascertain whether the length of the lay of the hemp and 

 Manilla round the strand was of that spiral which produced a maximum 

 strength, the yarn separated from the strand was also tested, and, compai-ing 

 the sum of the breaking-strains of the wire and yarn separately with the 

 whole in combination, this object was approximately gained. The summary of 

 results of these experiments will be seen in the two following Tables : — 



Table of the TensUe Breaking-strain of the Yarn (twisted) composing the 

 covering of the strands of Messrs. Glass, EUiott's Cables for the Atlantic 

 Submarine Telegraph. 



Summary of Eesults on Manilla and Hemp Yarn. 



Another very important question arises in the construction of this cable, 

 and that is the strength of the core and its conducting wire, and how it is to 

 be protected under a pressure of 7000 to 8000 lbs. per square inch when 

 lodged at the bottom of the ocean. This appears a question well entitled to 

 consideration ; and provided a properly insulated wii-e of one or more strands 

 can, without any exterior covering, be deposited in safety at these great 

 depths, it is obvious that the simpler the cable, the better. Assuming, there- 



