Encyclopædia Britannica, Ninth Edition/Electric Traction > 공지사항

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A serious objection to the storage system is the probable cost of renewing batteries. Under common situations it's possible that the conductor system has a slight benefit over the opposite on this respect, but the difference shouldn't be materials, particularly as the cost of power is a comparatively small part of the whole working expense of a line. All cables which have been manufactured and laid upon the rules which had been established in 1859 are yet in good working order, and every divergence from these principles has been at best however a costly experiment or utter failure. Reading the historical past of those first makes an attempt to put a community of cables at the underside of the ocean fifteen and twenty years in the past, is an effective deal like reading the old stories of the early voyages of discovery. This plan, just like the last, isn't relevant to metropolis streets. If, nevertheless, there are more than one train on the line, an automated block system is added to stop one from overtaking another by letting the part which a practice leaves stand insulated for a time.

We now know that there are exceptional localities the place there's motion within the water at a depth of 500 fathoms. Ten years ago it was generally believed that water had little or no movement under 50 fathoms, and one hundred fathoms was considered a degree of nice security. It's my very own opinion, and I'm authorized to say that it is usually the opinion of my pal Captain Halpin, who has laid all the cables from Suez to Australia, in addition to the French Atlantic cable (11,000 miles), and has additionally recovered and repaired cables from an ideal variety of depths, that a cable must be as heavy as it can be laid with security, and admit of being recovered in case of accident. The same agency laid an unprotected core from Varna to the Crimea, and it lasted till the winter set in; it is continuously said that it was cut by order of the French commander-in-chief, however there isn't a proof of this, and I am not disposed to believe it. There appear to have been mechanical difficulties in conserving the copper conductor in the centre of the insulating medium, so that the copper was typically discovered to be nearly seen beneath the light movie of gutta-percha which lined it.

As a gentle cable, to be manufactured in an ideal hurry, and laid to satisfy some emergency, it has a good deal of merit, but for a deep-sea cable I am of opinion that it would be discovered too incomplete and unfinished, and that difficulties could be skilled in laying which are not without delay foreseen, and that there would be no durability even when successfully laid. The Red Sea cable, covered externally with mild wires, and unprotected with bituminous compound, was so rusted in a short time that it could not be lifted for repairs. Experience about this time had established that a cable from the commencement of its manufacture to the time of its being laid should be tested underneath water and underneath pressure, and stored as a lot as doable below all the situations wherein it was meant to continue. The Red Sea and Indian cables are mentioned to have been imperfectly manufactured and laid too taut, but they weren't examined under water from the time of manufacture until they have been positioned at the underside of the sea, and this one grand omission, largely attributable to inexperience, is sufficient, without the recriminatory factors, to condemn to loss and failure any cable whatever.

These and many different examples have established the principle that no cable ought to be laid with out first acquiring an accurate survey of the method to the coast and touchdown-locations, with correct soundings over the supposed route, and as a lot knowledge as potential of the nature of the underside. The primary Atlantic cable failed principally on account of imperfect manufacture, in an awesome measure arising from undue haste and urgency, but largely owing to insufficient expertise. The primary cable ever manufactured with due regard to the precept of cautious supervision, testing below water, and being retained quietly in that situation until it was laid, was the Malta and Alexandria cable, laid in 1861. This cable was submerged in too shallow water, for many miles in much less depth than 20 fathoms; the consequence was the frequent recurrence of fracture from being rolled about by the surf, and but this cable was solely finally abandoned last yr; not because it couldn't be stored in restore, what is electric cable however as a result of it was too costly to keep in order. It has been urged that an iron-lined cable, suspended from one level to another, step by step turns into weaker, that rust and marine growth or deposit accumulate and break the cable with their weight; but I do not know of any instance in help of the assumption, nor is it at all sure that a easy unprotected core would exist for any size of time, or be in any approach higher adapted for the supposed situations.