新概念英语 第四册课文(7)

Henry Taylor, he went off immediately to visit him, carrying with him in his pocket what remained of a bottle of medicine formerly prescribed for an indisposition of Mrs Carlyle's. Carlyle was entirely ignorant of what the bottle in his pocket contained, of the nature of the illness from which his friend was suffering, and of what had previously been wrong with his wife, but a medicine that had worked so well in one form of illness would surely be of equal benefit in another, and comforted by the thought of the help he was bringing to his friend, he hastened to Henry Taylor's house. History does not relate whether his friend accepted his medical help, but in all probability he did. The great advantage of taking medicine is that it makes no demands on the taker beyond that of putting up for a moment with a disgusting taste, and that is what all patients demand of their doctors -- to be cured at no inconvenience to themselves.

Many strange new means of transport have been

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developed in our century, the strangest of them being perhaps the hovercraft. In 1953, a former electronics engineer in his fifties, Christopher Cockerell, who had

turned to boat-building on the Norfolk Broads, suggested an idea on which he had been working for many years to the British Government and industrial circles. It was the idea of supporting a craft on a' pad ', or cushion, of low-pressure air, ringed with a curtain of higher pressure air. Ever since, people have had difficulty in deciding whether the craft should be ranged among ships, planes, or land vehicles--for it is something in between a boat and an aircraft. As a

shipbuilder, Cockerell was trying to find a solution to the problem of the wave resistance which wastes a good deal of a surface ship's power and limits its speed. His answer was to lift the vessel out of the water by making it ride on a cushion of air, no more than one or two feet thick. This is done by a great number of ring-shaped air jets on the

bottom of the craft. It 'flies', therefore, but it cannot fly higher--its action depends on the surface, water or ground, over which it rides.

The first tests on the Solent in 1959 caused a sensation. The hovercraft travelled first over the water, then mounted the beach, climbed up the dunes, and sat down on a road.

Later it crossed the Channel, riding smoothly over the waves, which presented no problem.

Since that time, various types of hovercraft have appeared and taken up regular service--cruises on the Thames in London, for instance, have become an annual

attraction. But we are only at the beginning of a development

that may transport netsea and land transport. Christopher Cockerell's craft can establish transport works in large areas with poor communications such as Africa or Australia; it can become a 'flying fruit-bowl', carrying bananas from the plantations to the ports, giant hovercraft liners could span the Atlantic; and the railway of the future may well be the 'hovertrain', riding on its air cushion over a single rail, which it never touches, at speeds up to 300 m.p.h.--the possibilities appear unlimited.

Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea-surface and the hazards of navigation presented by the

irregularities in depth of the shallow water close to the land. The open sea was deep and mysterious,and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea-bed was flat. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1836 but it was not until 1800, when H.M.S. Porcupine was put at the disposal of the Royal Society for several cruises, that a series of deep soundings was obtained in the Atlantic and the first samples were collected by dredging the bottom.

Shortly after this the famous H.M.S. Challenger expedition established the study of the sea-floor as a subject worthy of the most qualified physicists and

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geologists. A burst of activity associated with the laying of submarine cables soon confirmed the Challenger's

observation that many parts of the ocean were two to three miles deep, and the existence of underwater features of considerable magnitude.

Today enough soundings are available to enable a relief map of the Atlantic to be drawn and we know something of the great variety of the sea-bed's topography. Since the sea covers the greater part of the earth's surface it is quite

reasonable to regard the sea-floor as the basic form of the crust of the earth, with superimposed upon it the continents, together with the islands and other features of the oceans. The continents form rugged tablelands w hich stand nearly three miles above the floor of the open ocean. From the shore-line out to a distance which may be anywhere from a few miles to a few hundred miles runs the gentle slope of the continental shelf, geologically part of the continents. The real dividing-line between continents and oceans occurs at the foot of a steeper slope. This continental slope usually starts at a place somewhere near the ice -fathom mark and in the course of a few hundred miles reaches the true

ocean-floor at 2,500-3,000 fathoms. The slope averages about 1 in 30, but contains steep, probably vertical, cliffs, and gentle sediment-covered terraces, and near its lower reaches there is a long tailing-off which is almost certainly the result of material transported out to deep water after being eroded from the continental masses.

Appreciation of sculpture depends upon the abi8lity to respond to form in three dimensions. That is perhaps why sculpture has been described as the most difficult of all arts; certainly it is more difficult than the arts which involve …… 此处隐藏：4961字，全部文档内容请下载后查看。喜欢就下载吧 ……