Before the prospectus was issued, every attention was paid that the characteristics of the Cable should be suited to its work; that it should not be too dense, lest its weight should render it unmanageable in the sea--nor too light, lest it should be at the mercy of the currents as it went down. It was decided that it should weigh a ton per mile, should be just so much heavier than the water which it displaced in sinking, and of such structure as could be easily coiled and yet be a rigid line, while its centre should be composed of wire capable of conveying electrical symbols through an extent of more than 2000 miles, and should retain complete insulation when immersed in the ocean. It was a subject of close and anxious inquiry how to obtain a Cable of this form and character. No fewer than sixty-two different kinds of rope were tested before one was determined on. In the Cable finally adopted, the central conducting wire was a strand made up of seven wires of the purest copper, of the gauge known in the trade as No. 22. The strand itself was about the sixteenth of an inch in diameter, and was formed of one straightly drawn wire, with six others twisted round it; this was accomplished by the central wire being dragged from a drum through a hole in a horizontal table, while the table itself revolved rapidly, under the impulse of steam, carrying near its circumference six reels or drums each armed with copper wire. Every drum revolved upon its own horizontal axis, and so delivered its wire as it turned. This twisted form of conducting wire was first adopted for the rope laid across the Gulf of St. Lawrence in 1856, and was employed with a view to the reduction to the lowest possible amount of the chance of continuity being destroyed in the circuit. It seemed improbable in the highest degree that a fracture could be accidentally produced at precisely the same spot in more than one of the wires of this twisted strand. All the seven wires might be broken at different parts of the strand, even some hundreds of times, and yet its capacity for the transmission of the electric current not destroyed, or reduced in any inconvenient degree. The copper used in the formation of these wires was assayed from time to time during the manufacture to insure absolute homogeneity and purity. The strand itself, when subjected to strain, stretched 20 per cent. of its length without giving way, and indeed without having its conducting power much modified or impaired.