tirsdag den 10. marts 2009

Cabels across the Atlantic

The first transatlantic cable was laid in 1858 after two failed attempts. How was a 1858-cable laying across the Atlantic constructed?

The cable manufactured was composed of seven copper wires closely connected or twined together, and protected by an exterior of three coats of gutta percha. Outside this again were six strands of yarn, and finally an external coating of wire, making the cable eleven-sixteenths of an inch in diameter. Its flexibility was so great as to allow of its being tied around the arm without injury, and its strength such that, if suspended vertically in water, it will bear six miles of its own length before breaking.

How was it laid?

The laying of the great Telegraph cable has necessitated the invention of new and even complicated machinery, while at the same time the accidental failure of the first attempt has brought about changes and improvements in the construction of the breaks and drums. We engrave, from drawings by our own correspondent, a complete representation of the machinery used. As is well known, the principal difficulty in the important undertaking is the even descent of the wire into the ocean without acquiring such velocity as to be broken by one of the sudden strains to which it is exposed, or coiling itself in a "kink." Of course the heavy swell of the Atlantic - and it must be remembered that even a calm implies a gigantic roll or swell of the mighty waves - will alternately raise and lower the vessel which is paying out the cable to such an extent as to necessitate a regulating power upon the descending wire, and in a gale of wind or on a chopping sea this necessity is vastly increased.. The machinery introduced for this purpose is admirably simple, and was contrived by Messrs. Easton and Amos, of Greenwich, England. It is placed on deck, in the afterpart of the vessel, and a little way to the right of the mizenmast. The cable, as it is uncoiled from the hold, passes over a horizontal groove and a deeply channelled wheel on to the great drums, around which it passes to another guiding wheel, and thence to the break machinery. These numerous windings preserve it from kinking, and the breaks are most ingeniously protected from the dangers of a too sudden jerk. Half between them and the stern is a grooved wheel, working on a sliding frame which is furnished with weights fixed on a rod, ending in a piston inside, or cylinder filled with water. This piston being somewhat less in diameter than the cylinder, leaves room for the water to circulate around it, although not without pressure. As, therefore, the cylinder is full, it is obvious that the play of the piston is impeded by the water, and that it will yield to pressure only gradually and not to a sudden jerk. It is now necessary to regulate the tension of the wire, which passes over the groove wheel and a block or sheaf, overhanging the stern, into the sea. The engineer weights the slide accordingly, the weight being hung on the shaft of the groove wheel under which the cable passes, and riding, therefore, on the cable itself. An index or dynamometer indicates the exact amount of pressure employed. Under this index is a steering wheel, which is connected with the weighting shaft, and a steersman, placed at this wheel, studies the index as he would a binnacle compass. The engineer instructs him as to the amount of pressure to be exerted, and a turn of the wheel suffices to relax or increase the strain. The abruptness of this, again, is guarded against by the water cylinder around the piston.

Both citations are from Frank Leslie's Illustrated Newspaper1858 Cable News

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tirsdag den 27. januar 2009

Africa’s Central Lake

From the 1954 book Engineers’ Dreams

Africa's Central Lake planned by german architect Herman Sörgel in 1935. Basically the plan was to totally reconfigure the interior of Africa by creating a series of huge inland seas. His plan was to dam the Congo River where it passes through a string of deep, narrow gorges after it merges with one of its tributaries, the Kwa River. It would create a lake 350,000 square miles in area - larger than the areas of California, Nevada and Oregon combined.

Once the lake filled, it would be forced to overflow from another one of its tributaries, the Ubangi, into the Shari River which is one of the feeders for the present day Lake Chad.
Lake Chad would swell to the dimensions it was thought to have had over 10,000 years ago, spreading across the Ahaggar plateau. A river would then be created that would lead through Algeria, turn east into Tunisia and then eventually empty into the Mediterranean Sea at the Gulf of Gabes. This river could made navigable allowing ships to directly access the interior of Africa.