Category Science

What is a Theodolite?

               A theodolite is an optical instrument used by surveyors for measuring horizontal and vertical angles. Using this instrument the map-makers can measure distances and directions to relate different places on Earth’s surface to each other. It is also used for precise angular measurements in the construction of roads, tunnel alignment, and other civil engineering works. Also the astronomers can measure the angle. It is called the system of triangulation. From these angles they can determine the distance of the Moon from the Earth. Now it is desirable that we should know about this useful instrument. 

               This instrument was developed in the 16th century by the English mathematician Leonard Digges. Over the years many modifications have been made in it. In its modern form, it consists of a telescope mounted to swivel both horizontally and vertically. Accurate horizontal levelling is done with the help of a spirit level. The cross hairs in the telescope eyepiece permit accurate alignment with the object sighted. When the telescope is adjusted precisely, the two accompanying scales — vertical and horizontal, are ready to give accurate readings of the angles. Then using the laws and theorems of geometry of triangles, the distances and other measurements are calculated.

               Theodolite is mounted on a tripod to obtain precise measurements. The transit is a variety of theodolite that has the telescope mounted in such a manner that it can be completely reversed or transited.

               The phototheodolite is a combination of camera and theodolite mounted on the same tripod, used in terrestrial photogrammetry for map-making and other purposes. 

What is an avalanche?

            An avalanche is a large mass of rock debris, snow, ice or soil that moves rapidly down a mountain slope, sweeping and grinding everything on its path. It takes place when a mass of material overcomes the frictional resistance of the sloping surface. It can be caused by spring rains, dry warm winds or violent vibrations produced by an artillery fire, thunder, man-made blasts or earthquakes. Changes in the depth, pressure and humidity of the snow itself can make one snow layer slide over another and result in an avalanche.

            There have been instances where huge avalanches have blocked rivers and buried towns. They are commonly composed of bed-rock fragments, a few centimeters thick in diameter and include a lot of soil and dust. The rock avalanches are thought to ride on a cushion of compressed air that allows them to travel long distances. A debris avalanche usually occurs in unconsolidated earth materials when weakened by moisture.

            Some snow avalanches occur during heavy snow storms. Sometimes they slide while the snow is still falling, but more often they occur after the snow has accumulated at a given site. One of the causes of snow avalanches is the slow formation of hexagonal cup-like ice crystals under the snow pack. The formation of these crystals creates a zone of weakness near the ground. These crystals act as a lubricant when the upper layers of the snow start sliding down the mountain. The wet avalanche is the most dangerous thing because of its massive weight, heavy texture and tendency to solidify as soon as it stops moving. The dry type is also equally dangerous because it’s entrapping of great quantity of air makes it act like a fluid.

            Sometimes, explosives are used to break large avalanches to control their intensity. Other measures such as snow-fences, wall and snow-bridges are erected on hillsides to check the fury of avalanches.

            Since the avalanches pose considerable threat to the mountain climbers, skiers, and travellers, they are being a subject of a lot of research and study. Geologists and scientists all over the world are working in close cooperation to identify the avalanche-prone areas and to monitor the danger of avalanches. Switzerland has established a Snow and Avalanche Research Institute to locate the avalanche-prone areas. 

What is a poison?

            A poison is a toxic substance that is damaging to life. When taken in excess, it causes irritation, soreness, roughness or redness, vomiting, nausea etc. Sometimes it can cause internal injury, sickness or even death. Poisons may be natural substances produced by living things like animals or plants. They can also be artificially made from different chemicals. Some minerals are also poisonous.

            There are different types of poisons: corrosive, irritant, systematic, gas poisons and food poisons. 

            The corrosive poisons kill the living tissues. In case of human beings it may damage the lining of the mouth or throat. Sodium hydroxide, some acids and phenols, are examples of corrosive poisons.

           

            The irritant poisons cause swelling and soreness of the muscous membranes. They may also damage the stomach, intestines or nerve centres. Some medicines, when taken in excess dosage, can act as irritant poisons. Some other can, make the body bleed inside. 

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What are the methods of sewage disposal?

          Sewage is a watery mixture of all wastes that come from different sources which include residential as well as non-residential places. It includes human wastes, soapy and dirty water from sinks and bathrooms, food scrabs and other garbage washed down the drains. More than 90 percent of sewage is the water used to wash the wastes away. A household might produce hundreds of gallons of sewage every day. Do you know how it is disposed?

          There are two ways of disposing the sewage. It can be stored in underground septic tanks until it gets soaked into the soil, or it can be dumped into rivers and oceans. The big cities may produce millions of gallons of sewage every day. Since the ground doesn’t have enough space for all of it, the cities are forced to dump the wastes into rivers and oceans. Unfortunately, this causes serious pollution.

          The sewage may be carried from homes in underground pipes which lead to a sewage treatment plant. Once in the plant, the sewage undergoes primary treatment. It removes the solid wastes by allowing them to sink to the bottom of a large tank. The liquid sewage is drained off the top and the solid sewage is collected from the bottom and burnt. Some sewage plants provide for only primary treatment. The liquid sewage is then poured into rivers.

          Most modern sewage treatment plants have equipments for a secondary treatment which remove the harmful germs and the floating wastes. The sewage is mixed with those bacteria that breakdown the wastes into harmless products. This process of destroying the waste kills off many germs. Large amounts of chlorine are then mixed into the water to kill all the remaining germs and other micro-organisms.

          Today many modern treatment plants have introduced a third step also. It removes the nutrients and chemicals that make water undrinkable. So, when the water passes through a tertiary treatment plant, it gets clean enough and can be drunk.

 

How is cheese made?

          Today, there are a variety of cheese made from the milk of different animals such as cow, goat, sheep, buffalo, mare, llama and yak. There are over 240 different kinds of French cheese because the French are the greatest cheese-eaters. They eat more than 18 kg cheese per person every year. The different varieties of cheese can be clubbed under two groups – hard and soft.

          Hard cheese is made from pasteurized whole milk ripened with a culture of lactic acid bacteria that converts some of the lactose into lactic acid. The milk proteins are then coagulated into a sort of ‘curd’ by the addition of rennet. Rennet contains the enzymes, rennin and pepsin, obtained from the stomach of young calves. This is useful to transform curdling milk to junket (junket is a custard like pudding made of milk). The junket is then cut into cubes to allow the liquid residue (whey) to separate. It is then heated to 38°C to drain off whatever whey might be left. It is then cut into blocks and pressed to remove the last traces of whey. These blocks of dry ‘curd’ are cut into small pieces and then salt is added to act as a preservative and to improve its flavour. Finally the cheese is produced by pressing the salted curd in moulds for about 48 hours and then ripening it under controlled temperature and humidity for three to six months. The ripening occurs on account of bacterial and enzyme action.

          Soft cheese is made in a similar way but with a major difference: the whey is left to drain off from the curd by gravity without applying any pressure or heat. The resulting cheese has high moisture content, between 50 to 70 percent, and they have mould cultures that excrete enzymes to give them the characteristic flavour. 

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Why do forward moving wheels sometimes appear turning backwards?

            You might have observed in a movie or on a television that the wheels of speeding automobiles sometimes appear turning backwards. Do you know what makes the forward-moving wheels appear going backwards? 

            To understand this strange optical effect, you have to understand the basic underlying principle of the motion picture. The film projected on the screen consists of a series of individual pictures. The pictures are joined together in such a manner that you can see them one after another in rapid succession. But there is a very small time, a fraction of a second, between each frame of picture when the screen is completely dark. Usually 32 pictures per second are shown on the screen, and they appear continuous because the impression of an image lasts for 1/16th of a second on the retina of our eye. 

            So in this case each individual picture shows the automobile moving along the road. However, if the wheel does not make a complete turn from one still picture to the next, it appears, as if, the wheel is moving backwards. For example, if we watch the top edge of the wheel in one picture, and if the edge does not make a complete turn in the next picture, but instead completes three-fourth of a turn, it looks as if the wheel turned one-fourth backward. Now in the third picture, with the wheel making only three-fourth of a turn, the top edge visible in the first picture is directly at the bottom. Again it appears, as if, the wheel has turned one-fourth backwards. Thus the automobile continues moving forward and wheels continue to appear to be going backwards. This is called the stroboscopic effect.