DEL CONTRATO ESTATAL

You should consult a physician and have a medical checkup before starting any extensive weight reduction program. The advice of a dietitian is also useful. An obese person may need psychological help as well, especially if the person is young and has been teased and made to feel guilty, hopeless, or worthless. Psychological treatment can help overcome these feelings so that obesity can be treated as a medical problem.

Diet. The first step in weight reduction is to develop a healthy diet that stops weight gain. Any reducing diet must provide fewer calories than a person uses. For example, people who eat 1,000 calories a day less than they use will lose about 2 pounds (0.9 kilogram) a week. Doctors generally advise most patients against trying to lose weight any faster.

The foods in a reducing diet must provide a well-balanced selection of all the nutrients needed for good health. There is no evidence that extreme diets--for example, "low carbohydrate" or "low protein" diets, or diets based on single foods--have any advantage over a balanced diet. For a complete discussion of well-balanced diets. In addition, the foods in a reducing diet should taste good and be easy to buy and to cook.

A weight reducer should aim to develop a realisticidea of the actual number of calories in various foods. Many people believe that such foods as baked potatoes and bread have many more calories than they do. People also underestimate the calories in such foods as steak.

Distribution of calories among meals and snacks is up to an individual. Some people can avoid hunger if they divide their calories among four or five light meals or snacks a day. Others can follow a diet better if they eat three meals a day and have no snacks.

Exercise. People on reducing diets must also increase their exercise. But an obese person--even one who is otherwise healthy--should not suddenly start a program of prolonged, strenuous exercise. An exercise program should be developed gradually to avoid dangerous strain on the heart or other body parts. One good way to start is to take daily walks and increase their length. More demanding exercises can be added as a person becomes fitter and thinner. A person should build up to five to six hours of exercise per week. Men over 40 years old, women over 50, and anyone with risk factors or symptoms of heart or lung disease should consult a physician before starting a vigorous exercise program.

Drugs. Doctors may prescribe drugs as part of a weight control program for carefully selected patients who are seriously obese. To be effective, these drugs must be combined with a reduced calorie diet and regular exercise. Patients should receive close medical supervision while taking any weight control medicine. Some such drugs have been linked with extremely serious side effects. Researchers are continuing their efforts to develop safe, effective drugs to help control weight.

Surgery. Extremely overweight people whose obesity is life-threatening and who cannot reduce with other methods may need an operation to reduce the size of their stomach. In one such operation, called gastroplasty or gastric stapling, a surgeon uses a large stapling device to close off most of the patient's stomach. After the surgery, the patient can eat only a small amount of food before becoming full.

SUPERSTITION

Superstition is a traditional belief that a certain action or event can cause or foretell an apparently unrelated event. For example, some superstitious people believe that carrying a rabbit's foot will bring them good luck. Others believe that if a black cat crosses their path, they will have bad luck. To yet other superstitious people, dropping a knife or fork on the floor means company is coming. Such beliefs are superstitions because in each case the action and the event it foretells are traditionally thought to be connected. For instance, the rabbit's foot is associated with fertility.

Superstitions have existed in every human society throughout history. Most people, including highly educated individuals, act superstitiously from time to time. Many people may joke about avoiding bad luck by knocking on wood or not walking under a ladder. But they have such beliefs anyway. Scholars once believed that all superstitions dated back to humanity's early history. But many superstitions have appeared in relatively recent times. According to a superstition in baseball, for example, a pitcher will give up a hit if anyone mentions that a no-hit game is being pitched.

Countless human activities are involved in superstitions. They include eating, sleeping, working, playing, getting married, having a baby, becoming ill, and dying. Times of danger and uncertainty have brought many superstitions. Superstitions concern animals, clothing, lakes, mountains, names, numbers, the planets and stars, the weather, and parts of the body.

Kinds of superstitions. Many superstitions deal with important events in a person's life, such as birth, entering adulthood, marriage, pregnancy, and death. Such superstitions supposedly ensure that a person will pass safely from one stage of life to the next. For example, a person born on Sunday will always have good luck. A bride and groom will have bad luck if they see each other on their wedding day before the ceremony. A pregnant woman must eat the right food, or she will give her child an unwanted birthmark. After a person dies, the doors and windows of the room should be opened so the spirit can leave.

Some superstitions involve a type of magic. One form of such magic comes from the belief that similar actions produce similar results. Many people believe a newborn baby must be carried upstairs before being carried downstairs. In this way, the child will be assured of rising in the world and having success. The same principle appears in the custom of putting money in a purse or wallet being given as a gift. The giver wants to make sure the purse or wallet will always contain money.

A number of superstitions involve someone's taking a deliberate action to cause something to happen or to prevent something from occurring. Most of these causal superstitions involve ensuring good luck, avoiding bad luck, or making something good happen. For example, carrying a silver dollar supposedly brings good luck. Some people will not start a trip on a Friday, especially if it is the 13th day of the month. Friday and the number 13 are both associated with bad luck. According to a Japanese belief, the number 4 is unlucky. This is because shi, the Japanese word for 4, sounds like the Japanese word for death. Thus, many buildings in Japan have no fourth floor. According to another superstition, wedding guests throw rice at the newlyweds to ensure that the marriage will result in many children. In some cases, causal superstitions involve actions intended to give bad luck to someone. Witches supposedly perform some of these actions.

Other superstitions foretell an event without any conscious action by the person involved. Some of these sign superstitions foretell good or bad luck. For example, finding a horseshoe or a four-leaf clover means good luck. Breaking a mirror or spilling salt brings bad luck. Other sign superstitions foretell a certain event or condition. A ring around the moon means rain will soon fall. A howling dog means death is near. A person with red hair has a quick temper.

The role of superstitions. Many people scoff at superstitions because they consider such beliefs to be unscientific. However, many scholars believe that some superstitions have a scientific basis. For example, people in England once used tea made from foxglove plants to treat some forms of heart disease. Today, physicians often prescribe digitalis, a drug made from dried leaves of the purple foxglove, for patients with weak hearts.

Some superstitions have a practical origin. For example, many people believe that lighting cigarettes for three individuals from one match will bring bad luck. This superstition may have originated among soldiers during World War I (1914-1918). At night, a match that stayed lit long enough to light three cigarettes provided a target for the enemy. Another superstition involves hanging a bag of garlic around a child's neck for protection from illness. The garlic-filled bag has no supernatural power. But its smell keeps away other children—including any who have a disease that the wearer of the bag might catch.

Most people have fears that make them insecure. Superstitions help overcome such fears by providing security. They reassure people that they will get what they want and avoid trouble. For example, millions of people believe in astrology and base important decisions on the position of the sun, moon, planets, and stars. Superstitions will probably have a part in life as long as people fear each other and have uncertainties about the future.

RELATIVITY

Einstein's theory of relativity has caught the imagination of the average person more than any other physical theory in history. Yet the theory of relativity, unlike many other results of physical science, is not easily understood by the average person. We can understand the relativity theory fully only by means of the mathematical formulas which make it up. Without mathematics, we can only state some of its basic ideas and quote, but not prove, some of its conclusions.

The relativity theory deals with the most fundamental ideas which we use to describe natural happenings. These ideas are time, space, mass, motion, and gravitation. The theory gives new meaning to the old ideas that these words represent. It is basically made up of two parts. One is the special, or restricted, relativity theory, published by Albert Einstein in 1905. The general relativity theory was put forward by Einstein in 1915.

Special theory of relativity

This theory is called the special relativity theory because it refers to a special kind of motion. This is uniform motion in a straight line, that is, with constant velocity.

Suppose we are on a smoothly running railroad train which is moving at a constant velocity. In this train you may drop a book, play catch, or allow a pendulum to swing freely. The book will appear to fall straight down when it is dropped; the ball will travel directly from the thrower to the catcher. All these activities can be carried on in much the same way and with the same results on the ground outside the train. So long as the train runs smoothly, with constant velocity, none of our mechanical activities will be affected by its motion.

On the other hand, if the train stops or speeds up abruptly, our activities may be changed. A book may be jarred from a seat and fall without being dropped. A ball will travel differently.

One way of stating the principle of this theory is to say that the laws of mechanics are the same for an observer in a smoothly moving train as for the observer on the ground. Physicists would say: If two systems move uniformly relative to each other, then all the laws of mechanics are the same in both systems. This principle may be called the classical relativity principle. This principle is as old as the ideas of mechanics and physics.

Suppose we have a long train much like the train in the previous example. But instead of rolling along at a normal speed, it will be moving uniformly at a speed of, let us say, 20,000 miles (32,000 kilometers) a second. Instead of having two persons playing catch on the train, we will have a radio antenna on the train sending out radio waves, or a flashlight sending out light signals. Observers on the train will measure the velocity of the radio waves and light signals. On the ground we will also have an antenna or flashlight, and observers measuring the velocity of the signals. Is the velocity of the radio or light waves the same for those on the ground as it is for those on the train? Physicists in the late 1800's would have answered, "No." They would have said the classical relativity principle holds true for mechanical activities, but not for those of electromagnetic waves--that is, not for radio or light waves.

A physicist would have said that radio and light waves travel through ether at a velocity of 186,282 miles (299,792 kilometers) per second. Ether was a substance that scientists imagined to fill all space, to account for the transmission of light in outer space. The physicist would have said that the stars, sun, planets, and our imaginary moving train move through the ether sea at different speeds. Thus, the velocity of light will be different for an observer on the sun, on the earth, and on the train.

reference. Ether was looked upon as a fluid or elastic solid. It was believed to occupy the spaces between the atoms that made up matter. It offered no resistance to the earth's movement.

Among the many experiments which helped destroy the ether theory, the most famous is that of Michelson and Morley in 1887. Their measurements of the speed of light showed that the motion of the earth as it moved around the sun had no influence upon the velocity of light. Therefore, light has a uniform velocity, regardless of the frame of reference. This experimental result seemed strange, since normally we expect the speed of an object to depend on how fast the observer is moving.

Einstein asserted that the relativity principle was true for all phenomena, mechanical or electromagnetic. In other words, there was no special, or nonmoving, frame of reference for electromagnetic phenomena.

The basic ideas of the special relativity theory are found in a mathematical formulation of two postulates. The first is that the relativity principle is valid for all phenomena. The second postulate is that the velocity of electromagnetic waves, or light, in empty space is constant, and furthermore is independent of the velocity of its source or observer.

The following deductions have been made from these postulates by mathematical means.

According to the special relativity theory, a material body can only move with a velocity lower than that of light.

If a conductor on a fast-moving train compared his clock with the many clocks in the stations he passed, he would find that the rhythm of his clock is faster than the rhythm of the clocks on the ground. On the other hand, it will appear to the stationmasters that the rhythms of their clocks are faster than the rhythm of the conductor's clock on the train passing the station. This effect is small, and could be detected only if the velocity of the one clock that passes many others were not very small compared with the speed of light.

Two events judged as taking place at the same time by the observer in the train may not be simultaneous for the observer on the ground.

The length of every object resting in the train appears to the observer outside to be shortened in the direction in which the train is moving.

Perhaps the most important of these deductions is the fact that mass is not unchangeable. The mass of an object increases with its velocity. Theoretically, the mass of an object would become infinite if its velocity became the velocity of light. This mass increase has been observed with experiments. A small particle of matter accelerated to 86 per cent of the speed of light has twice as much mass as it does when it is at rest.

The theory also shows a relation between a body's mass and its energy (E equals m times c- squared). This relation has great practical importance in the liberation of the energy in the nucleus of an atom. When energy is liberated from the nucleus of the uranium atom and atoms of other elements are formed, the total mass of these atoms is less than the total mass of the uranium atom. This means that some of the mass of the nucleus of the uranium atom has been transformed into energy. The E equals m times c-squared law shows that the energy in a single uranium nucleus is 220,000,000,000 electronvolts, providing that all its mass could be converted to energy. However, splitting the uranium nucleus, a process known as fission, releases only 0.1 per cent of the total energy content. This amount is still about a million times greater than the energy released in the burning of chemical fuels.

Various experiments have proved the truth of many of these conclusions about relativity. In 1938, H. E. Ives used a hydrogen atom as a moving clock. He found that a fast-moving hydrogen atom does slow down in its rhythm, just as Einstein predicted the moving clock would do. This slowing down could be shown by a change in the frequency of the line given off in its spectrum. The changes of

mass as predicted by the special theory of relativity are observed in machines that are used to accelerate electrons and nuclear particles to the high speeds necessary to study nuclear properties.

The mathematician H. Minkowski gave a mathematical form to the special relativity theory in 1907. A line involves only one dimension. We can locate any point on a sheet of paper by measuring from that point to any two sides of the paper that are perpendicular to each other. Therefore, we can say that any point on a sheet of paper involves two dimensions. All points in space involve three dimensions: height, length, and breadth. But there is one other important fact involved. In physics as well as history we must deal with events. When and where did the French Revolution start, for example? When and where does the earth have the smallest velocity in its movement about the sun? Events must be characterized by four numbers, bringing in the idea of a fourth dimension. Three of these numbers answer the question where; one must answer the question when. Answering the question when involves the idea of time. Then we consider things in terms of four dimensions.

This question of answering when and where an event took place becomes more complicated, according to the theory of special relativity, because rods can change their lengths, and clocks change their rhythms, depending on the speed at which they operate when they are in motion. Therefore, we must answer the questions when and where an event took place in terms of a definitely moving system, or in terms of the relationships between two moving systems. For example, if we know when and where an event took place for an observer on our swiftly moving train, and if we know the velocity of the train, we can find out when and where the same event took place for an observer on the ground. The mathematical formulation of the theory of special relativity