MECHANICAL PROPERTIES OP THE PROPOSED ATLANTIC CABLE. 415 



wires elongate by tension, and that to a degree highly injurious to the gutta 

 percha insulator, which contracts the already stretched wires, producing a ten- 

 dency to force themselves in loops through the covering in which they are 

 incased. To prevent those injurious effects it is necessary to protect the core 

 by an outside covering of strong material, to relieve it from severe tension, and 

 also to protect the gutta percha from injury. 



Regarding this as a circumstance of great importance beai'ing directly 

 upon the ultimate strength of the cable, the Committee arrived at the con- 

 clusion that the cable No. 4G, composed of homogeneous wire, calculated to 

 bear not less than from 850 to 1000 lbs. per wire, with a stretch of f^^ths of 

 an inch in 50 inches, was the most suitable for the Atlantic Gable. 



Impressed with these views the Committee therefore recommended this 

 cable, the particulars of which will be seen in the following specification : — 



Sjjecification of No. 46 Cable. 



The conductor consists of a copper strand of seven wires (six laid round 

 one), each wire gauging '048 (or No. 18 of the Birmingham wire-gauge), the 

 entire strand gauging -144 inch (or No. 10 Birmingham gauge) and weigh- 

 ing 300 lbs. per nautical mile, embedded for solidity in the composition known 

 as " Chatterton's Compound." 



The insulator consists of gutta percha, four layers of which are laid on 

 alternately with four thin layers of Chatterton's compound, making a dia- 

 meter of the core of -404 inch and a circumference of l-y92 inch. The 

 weight of the entire insulator is 400 lbs. per nautical mile. 



The External Protection. — This is in two parts. First the core is sur- 

 rounded with a padding of soft jute yarn, saturated with a preservative mix- 

 ture. Next to this padding is the protective covering, which consists of ten 

 sohd wires of the gauge -095 inch, drawn from homogeneous iron, each wire 

 surrounded separately with live strands of Manilla yarn saturated with a 

 preservative compound, the whole of the ten strands thus formed of the hemp 

 and iron being laid spirally round the padded core. 



The weight of this cable in air is 34 cwt. per nautical mile ; the weight 

 in water is 14 cwt. per nautical mile. The breaking-strain is 7 tons 15 cwt., 

 or equal to 11 times its weight per nautical mile in water, that is to say, if 

 suspended perpendicularly, it woidd bear its own weight in 11 miles' depth of 

 water. The deepest water to be encountered between Ireland and Newfound- 

 land is about 2400 fathoms ; and one mile being equal to 1014 fathoms, there- 

 fore 1014x11= ^,^, =4-64, the cable having thus a strength equal to 

 2400 o 1 



4-64 times of its own vertical weight in the deepest water. 



In this report we have not entered upon the process of immersion, either 

 in tanks or the sea ; we have confined our attention exclusively to the cable 

 and the quality of the materials of which it should be composed, and the 

 questions of coiling, shipping, submersion, &c., we have left for future 

 inquiry. 



