Методические указания по английскому языку по дисциплине английский язык предназначены для студентов изоп нгау всех направлений подготовки.
Скачать 1.3 Mb.
|
DISC PLOUGHSThere are various ways of making the initial cut. To lessen the amount of soil that can bank up by fences, some operators prefer to do the initial round with the rearmost disc cutting full depth and the depth of the others tapering off to zero at the front furrow wheel. This means that with the plough level the furrow wheels are raised until the discs just touch the ground, and the landwheel is then raised to a height equal to the desired depth. This method saves adjusting the front furrow wheel on the second round, but it is difficult to control the depth of the rearmost disc, and of course the depth varies across the gang of discs. Another way is to raise all the wheels to a height above ground equal to the desired depth, remove the last two or three discs, set the width to, say 60 per cent of the full width and plough. This method gives even depth because all the wheels run on the unploughed land, but requires adjustment of the front and rear furrow wheels for subsequent rounds. After the initial furrows have been cut and the wheel heights set correctly, the plough can be set for normal operation. Some features and characteristics of a plough are fixed by the designer; others are adjustable and must be decided by the operator. For example, the operator can change the width of cut, the depth, wheel toe-in or drift angles, the lateral position and the height of the drawbar, the amount of ballast and the speed. He cannot change the tilt angle of the discs (except by such extreme measures as blocking the stump-jump mechanism) or their angle of attack at any particular furrow width; these all have a large influence on the operating characteristics of a plough, but are fixed by the designer. So the operator must decide settings for: Width and depth of cut. In general, when ploughing on light soils, the plough can be set fully open, and on heavy or clayey soils it should be set initially at about two-thirds of full width. When properly adjusted, the resulting depth will depend on the width and the weight of the plough; this is dealt with in detail below. Wheel angles. All the wheels can be set to toe-in towards the ploughed land at a small angle of say, five degrees initially. Drawbar location. The drawbar should be parallel to the furrow, pointing initially at the centre of the gang of discs; its final position laterally will be found to be within 10 inch. either side of this centre, depending on the make of plough. The centre of the gang is taken relative to the cutting edge of the discs; for an 18-disc plough, for example, if the drawbar is pointed at the bearing-cap of the ninth disc, it will be on a line approximately midway between the ninth and tenth discs. The drawbar height should be low to keep sufficient weight on the rear wheel; the reasons are given later. SPECIALIZED FARM MACHINESNo end of other specialized harvesters are in existence, each of them specially designed for the purpose intended. Thus, we find cotton harvesters, pea harvesters, tomato harvesters, and even cherry and orange harvesters. For harvesting root and tuber crops there exist various diggers, such as potato diggers, carrot diggers, onion diggers, even up to special sweet-potato diggers. But perhaps the best labour-saving devices are tuber and root harvesting combines among which the potato harvester stands out with particular prominence. This machine is, as a rule, not self-propelled, but actuated by a PTO from a tractor. Its main components are the shares, a haulm remover or topper, a chain elevator, a clod breaker, a lifting drum covered with polyethylene wire and a sorting table. The shares simultaneously dig down two potato rows. The mass dug out passes to the chain elevator whereupon the clods are broken by the clod breaker and the tubers separated. At the same time the removed haulm is thrown aside on the field. The tubers, separated from the clods, now pass over to the lifting drum which feeds them onto the sorting table which separates the tubers from the remaining earth. Finally the clean potatoes are fed into a bin. It is widely admitted that hay crimping is a fast, efficient, short cut to higher quality hay. It reduces, after mowing, the loss that results from long exposure in the field and handling the hay crop. Crimping cuts down the risks of obtaining poor hay by shortening the time the crop is exposed to the weather and prevents the mechanical damage that so often goes with outdated haymaking methods. More and more research is being carried out in the world on modern methods of haymaking and time after time this research proves that crimping the crop immediately after mowing is the surest, safest and most desirable way of making higher quality hay. When grass is mown and no special measures are taken moisture is lost rapidly from the leaf and slowly from the stem. When the stem is fit to bale the leaf is so dry that it will shatter when it is touched. It stands to reason that to avoid this it is essential to equalise the drying rate of the stem and the leaf. The longer the crop is left out in the weather the greater is the loss of feed value. This is the field where the crimper can help by equalising the drying rate of the stem and the leaf which eliminates the most undesirable features of conventional haymaking methods. Cotton takes perhaps the leading place among all industrial crops. For the harvesting of cotton up to quite recent times manual methods alone were used. But today, with the advent of comprehensive mechanization, most, if not all, labour-consuming kinds of labour are being taken care of by labour-saving devices. Among ,them the cotton picker stands out with particular prominence. The cotton picker is usually tractor-mounted. Sometimes its working mechanisms operate from a PTO. During one pass this machine gathers cotton from two rows of the cotton plant. It consists of two limb-lifters, two doffers with cotton-picking receptacles, two fans, air-ducts and a bin. The limb-lifters raise the laid plants, compress the bottom part of the stalk and feed it into the cotton-picking receptacle. Here the limbs pass between two rotating drums which with their teeth extract the cotton out of the opened bolls and wind it upon their spindles. Then the drums draw the spindles from the bush and feed it to the doffing brushes which, in rotating, remove the raw cotton. A current of air passing from the fan through the air- duct now sends the removed cotton into a bin. The cotton picker is manned by a single operator and it replaces the need to have twenty manual pickers. Other -agricultural machines comprise stubble cleaners, ploughs of various description such as general purpose ploughs, breaker ploughs, garden ploughs, orchard ploughs, etc; sweeps; tine, zigzag and disc as well as weeding harrows, drills which may be all-crop or specialized such as grain, beet, bean, carrot, etc.; manure spreaders, etc. Along with machinery specially intended for seeding, tillage, cultivation, fertilization, thinning and other kinds of field work extensive use is at present made-of various devices for protecting plants against pests, diseases and weeds. Widely used are rain-guns and sprayers — turbine mist blowers, aerosol foggers and fumigators. All these machines have the common feature of raining a finely divided spray of various disinfectant chemicals over the plantations, forming a kind of fog, smoke or mist, which destroys the noxious elements, that would otherwise affect normal plant growth. There also exist many machines for processing agricultural products. They comprise special machines for the preparation of dairy products, honey, wine, cider, vinegar, oils (vegetable and essential), sugar (cane, beet and maple) syrups and preserves. The production of dairy products such as milk, cream, butter, curds and the like is both mechanical and chemical. Of prime importance is the processing of cereals. The processing is effected partly on the farm and partly at factories. Among the most important stationary machines are chaff-cutters which cut straw and hay into short lengths to facilitate mixing with other feeds. Next come mills (crushing, grinding). These machines provide a degree of grinding which is very coarse compared with flour. Crushers are used mainly for oats, maize and linseed (flaxseed). The material is fed from a hopper by gravity and the machines are generally power-driven. Grinders utilize small disks revolving at a high speed. Sometimes they are provided with a meal-sifter and then corn can be ground sufficiently fine for making whole-meal bread. The great invention of James Watt By the middle of the 18th century, however, the childhood of the steam-engine was already drawing to an end. A young Scotsman by the name of James Watt, the fifth son of a ship's carpenter gave the machine its most efficient form -and thereby helped to revolutionize the British way of life. A manufacturer from Soho, near Birmingham, Boulton, made James Watt his partner in the world's first steam-engine factory. Soon the firm of Boulton & Watt became one of the wonders of the age: here the visitors, who turned up from all over Europe and even America, could see the shape of things to come. Boulton made Watt think of ways and means to convert the reciprocating movement of the engine into a rotary one for use in factories and, later perhaps, for vehicles and ships. Watt produced no less than five different solutions, the best of them being the 'sun-and-planet' system - we are so familiar with it that we hardly realize what an excellent solution to a tricky problem it is. Watt also adopted an old invention, the fly-wheel, for the important purpose of turning the irregular motion of the piston into a regular, rotary one. The fly-wheel is, in fact, a reservoir of energy, which it 'stores up' during the working stroke of the engine, to release it as the crank passes through the dead centre. Neither could he have known that he invented one of the major 'feed-back' devices-which play such a vital part in automation, where they act as automatic controls. This is the 'governor', whose task it is to keep the engine speed constant, detect an unnecessary or dangerous increase of engine power, and to reduce it by closing the throttle or steam-valve. The Watt governor works simply by using centrifugal force: a vertical shaft, carrying two heavy metal balls at the ends of arms, is rotated by the engine, and centrifugal force moves the balls outwards as the engine speed increases, or allows them to sink as the speed decreases. The arms to which the balls are fixed move therefore up or down, raising or lowering a 'collar' around the vertical shaft. This is connected to the throttle or steam-valve, closing or opening it if the engine speed becomes too great or too low. Thus the steam-engine controls itself. 'The people of London, Manchester, and Birmingham are steam-mill mad', Boulton told Watt in 1781. The Soho factory turned out as many steam-engines as possible, yet the demand surpassed by far its production capacity, and other manufacturers' were permitted to build them under Watt's licence. Why was there now such an enormous demand for energy, after centuries of indifference and even hostility towards the idea of Using the forces of Nature for benefit of mankind? Slowly, the medieval system of the individual craftsman had begun to crumble. In England a new form of industry appeared, timidly at first: groups of men banded together to use machines which were too costly and too heavy for the independent artisan. Merchants' who needed wares to sell provided the money and organized the manufacture, or 'factory'. These 'capitalists' employed the workers for wages. They appeared first in those trades where heavy machinery and capital was most necessary: mainly in coal-mining, where the early steam pumps saved many pits from ruin through flooding, and in textile production, where a number of inventions were revolutionizing spinning and weaving. It was through the impact of these new machines that Britain hitherto a nation of farmers, turned into an industrial state - and that Englishmen left the countryside by their many, thousands to crowd into the towns and seek employment in the factories which seemed to promise work and livelihood for all. Spinning and weaving, a most important industry in a cold, northern climate had been carried out in the villages with spinning-wheels and hand looms; but although the cloth produced in this way was expensive, the men and women who made it lived in poverty from the cradle to the grave. Only a substantial rise in the level of production could have increased the country's standard of living. Taxes took away much of the people's earnings, and feudal restrictions prevented a free exchange of goods and services. The new machines broke through this barrier, changing an old-fashioned handicraft to modern mass production. John Kay, a poor clockmaker from Lancashire, made the beginning with his 'fly shuttle', a little box on either side of the loom, where the shuttle remained between its journeys across the warp threads. Each box had a little rod, one end of which was fastened to a cord, and when the cord was pulled the rod hit the shuttle and shot it across the loom into the little box on the other side. Then the cord on the other side was pulled, and the shuttle flew back again. Thus the weaver- instead of throwing the shuttle across and back again by hand - could work much faster, and the width of the cloth could be doubled. John Kay made his invention in 1733. Thirty-five years later, a weaver, James Hargreaves invented a spinning machine - which he called 'Spinning Jenny' after his wife -with eight spindles operated by a single wheel. Later he built a machine with thirty spindles. Richard Arkwright, a barber by profession, heard the weavers in his home town complain that the yarn produced by the new spinning-jenny was not as fine and smooth as that spun by the old method. With the help of a watch-maker he built a new machine which squeezed the wool or cotton into long, flat strands and then twisted them into smooth threads. The machine was good but heavy and could be worked only by power; as it was first worked by water power it became known as the 'water-frame'. At the turn of the century a young university graduate from Massachusetts, Eli Whitney revolutionized cotton harvesting by his invention of the 'cotton gin'. Negro slaves had been used in the southern states of the USA to separate the fibre from the seeds by hand; the gin did it mechanically. It was this machine which influenced the development of the whole of the United States more than any other; cotton became the country's great source of wealth. When Whitney first introduced his machine, the USA produced no more than 140,000 lb. of cotton per year: in 1800, only a few years later, the figure was 35 million pounds. All these inventors had to struggle hard against prejudice and fear, most of all among the workers, who were worried about losing their jobs when those new machines would start to produce more and more goods. There were riots, some inventors were driven out of the country, others died penniless. But the men who built the new factories saw that these machines could offer them enormous profits. They installed them, bought steam-engines to power them, and the workers had to come willy-nilly to ask for jobs in the factories if they wanted to make a living. Early days of electricity There is electricity everywhere in the world. It is present in the atom, whose particles are held together by its forces; it reaches us from the most distant parts of the universe in the form of electro-magnetic waves. Yet we have no organs that could recognize it as we see light or hear sound. We have to make it visible, tangible, or audible, we have to make it perform work to become aware of its presence. There is only one natural phenomenon which demonstrates it unmistakably to our senses of seeing and hearing - thunder and lightning; but we recognize only the effects - not the force which causes them. Small wonder, then, that Man lived for ages on this earth without knowing anything about electricity. He tried to explain the phenomenon of the thunderstorm to himself by imagining that some gods or other supernatural creatures were giving vent to their heavenly anger, or were fighting battles in the sky. Thunderstorms frightened our primitive ancestors; they should have been grateful to them instead because lightning gave them their first fires, and thus opened to them the road to civilization. It is a fascinating question how differently life on earth would have developed if we had an organ for electricity. We cannot blame the ancient Greeks for failing to recognize that the force which causes a thunderstorm is the same which they observed when rubbing a piece of amber: it attracted straw, feathers, and other light materials. Thales of Miletos, the Greek philosopher who lived about 600 B. C, was the first who noticed this. The Greek word for amber is elektron, and therefore Thales called that mysterious force 'electric'. For a long time it was thought to be of the same nature as the magnetic power of the lodestone since the effect of attraction seems similar, and in fact there are many links between electricity and magnetism. There is just a chance, although a somewhat remote one, that the ancient Jews knew something of the secret of electricity. Perhaps the Israelites did know something about electricity; this theory is supported by the fact that the Temple at Jerusalem had metal rods on the roof which must have acted as lightning-conductors. In fact, during the thousand years of its existence it was never struck by lightning although thunderstorms abound in Palestine. There is no other evidence that electricity was put to any use at all in antiquity, except that the Greek women decorated their spinning-wheels with pieces of amber: as the wollen threads rubbed against the amber it first attracted and then repelled them - a pretty little spectacle which relieved the boredom of spinning. More than two thousand years passed after Thales's discovery without any research work being done in this field. It was Dr. William Gilbert, Queen Elizabeth the First's physician-in-ordinary, who set the ball rolling. He experimented with amber and lodestone and found the essential difference between electric and magnetic attraction. For substances which behaved like amber - such as glass, sulphur, sealingwax - he coined the term 'electrica', and for the phenomenon as such the word 'electricity'. In his famous work De magnete, published in 1600, he gave an account of his studies. Although some sources credit him with the invention of the first electric machine, this was a later achievement by Otto von Gue-ricke, inventor of the air pump. Von Guericke's electric machine consisted of a large disc spinning between brushes; this made sparks leap across a gap between two metal balls. It became a favourite toy in polite society but nothing more than that. In 1700, an Englishman by the name of Francis Hawksbee produced the first electric light: he exhausted a glass bulb by means of a vacuum pump and rotated it at high speed while rubbing it with his hand until it emitted a faint glow of light. A major advance was the invention of the first electrical condenser, now called the Leyden jar, by a Dutch scientist, a water-filled glass bottle coated inside and out with metallic surfaces, separated by the non-conducting glass; a metal rod with a knob at the top reached down into the water. When charged by an electric machine it stored enough electricity to give anyone who touched the knob a powerful shock. More and more scientists took up electric research. A Russian scientist Professor Richmann from St. Petersburg, was killed when he worked on the same problem. Benjamin Franklin, born in Boston, was the fifteenth child of a poor soapboiler from England. He was well over 30 when he took up the study of natural phenomena. 'We had for some time been of opinion, that the electrical fire was not created by friction, but collected, being really an element diffused among, and attracted by other matter, particularly by water and metals,' wrote Franklin in 1747. Here was at last a plausible theory of the nature of electricity, namely, that it was some kind of' fluid'. It dawned on him that thunderstorms were merely a discharge of electricity between two objects with different electrical potentials, such as the clouds and the earth. He saw that the discharging spark, the lightning, tended to strike high buildings and trees, which gave him the idea of trying to attract the electrical 'fluid' deliberately to the earth in a way that the discharge would do no harm. In order to work this idea out he undertook his famous kite-and-key experimenti in the summer of 1752. It was much more dangerous than he realized. During the approach of a thunderstorm he sent up a silken kite with an iron tip; he rubbed the end of the kite string, which he had soaked in water to make it a good conductor of electricity, with a large iron key until sparks sprang from the string -which proved his theory. Had the lightning struck his kite he, and his small son whom he had taken along, might have lost their lives. In the next experiment he fixed an iron bar to the outer wall of his house, and through it charged a Leyden jar with atmospheric electricity. Soon after this he was appointed Postmaster General of Britain's American colonies, and had to interrupt his research work. Taking it up again in 1760, he put up the first effective lightning - conductor on the house of a Philadelphia business man. His theory was that during a thunderstorm a continual radiation of electricity from the earth through the metal of the lightning-conductor would take place, thus equalizing the |
Похожие:
 | Методические указания предназначены для студентов 2 курса всех специальностей заочной формы обучения |  | Методические указания предназначены для выполнения практических работ учебной дисциплины «Английский язык» для студентов 1, 2 и 3... |
| Методические указания предназначены для самостоятельного изучения студентами дисциплины и их подготовки к зачётам | | Методические указания предназначены для студентов II-IV курсов очной формы получения образования спо всех профилей |
| Методические указания предназначены для студентов I курса всех технических специальностей нгту, изучающих английский язык (уровень... | | Методические указания предназначены для студентов I курса всех технических специальностей нгту, изучающих английский язык (уровень... |
| Методические указания предназначены для студентов 3 курса заочной формы обучения специальности 15. 02. 08 «Судостроение» | | Методические указания предназначены для студентов 3 курса заочной формы обучения специальности 26. 02. 06 «Эксплуатация судового... |
| Методические указания предназначены для студентов 3 курса заочной формы обучения специальности 26. 02. 06 «Эксплуатация судового... | | Апалькова В. Г. Английский язык. Рабочие программы. Предметная линия учебников «Английский язык в фокусе» 5-9 классы. Просвещение,,... |