Facts about Caesars (title)

Julius Caesar

• The Caesars were rulers of ancient Rome.
• The words "czar" and "kaiser" both came from the word "Caesar.
• " "Caesar" was at first the last name of a famous ruler, Julius Caesar. Then it became a title that meant "emperor."
• The change from being a familial name to a title adopted by the Roman Emperors can be dated to about AD 68/69, the so-called "Year of the Four Emperors".
• The first known bearer of the name "Caesar" was one Numerius Julius Caesar (born before 300 BC)
• After one of his battles in Asia, Julius Caesar sent back a famous message to Rome. It is famous because it told so much in so few words. The message was Veni, vidi, vici. Translated into English the message is, "I came, I saw, I conquered."
• The month of July was named for him.
• Gaius Julius Caesar Augustus is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in AD 14

Interesting facts about Life

new born

• Life, characteristics of Life, or the condition of being alive, is one of the mysteries of science.
• Biology is the science that deals with the study of life.
• All living beings are made of the same materials as nonliving things, but living things can do things that nonliving things cannot do. They can move, grow, and reproduce. They are made of cells. They react to things around them.
• More complex living organisms can communicate through various means.
• The first characteristic of life is the ability to move. A person can get up and move when he wants to. Plants also move, but the movement can frequently be seen only with a microscope. However, a rock or a piece of paper cannot move unless some force, such as the wind, or a person, makes it move.
• All living things are made of cells and grow from the inside out.
• Some of the earliest theories of life were materialist, holding that all that exists is matter, and that all life is merely a complex form or arrangement of matter.
• Vitalism is the belief that the life-principle is essentially immaterial.
• The ability to respond to a stimulus is an important function of living things. The sun acts as a stimulus for many plants, and they respond to it by moving or turning towards it. If the telephone rings, a person responds to this stimulus by jumping up and running to answer it.
• It is still a challenge for scientists and philosophers to define life in unequivocal terms. Defining life is difficult—in part—because life is a process, not a pure substance.
• Earth is the only planet in the universe known to harbor life. 
• Death is the permanent termination of life.

facts about Linen

• Linen is a fabric or yarn made from flax.
• Garments made of linen are valued for its exceptional coolness and freshness in hot weather.
• Flax is the earliest vegetable fiber ever used. Linen 5,000 years old has been found in Egyptian tombs.
• According to some studies, linen effectively reduces the perspiration rate of a person 1.5 times more than cotton clothes, and twice more than viscose clothes. 
• All through history, linen has been used throughout the world.
• The word "linen" is cognate with the Latin for the flax plant, which is linum, and the earlier Greek linon.
• Today, Ireland is the chief producer of linen. The finest flax fiber is from Belgium.
• The best linen yarn must be made hand.
• France, Germany, England, and the Netherlands are large producers of flax.
• The beauty of linen consists in the evenness of the thread. Linen with a round thread is considered better than that wi a flat thread.
• The heaviest linens are made into tents, sailcloth, canvas, carpets, and carpet backings.
• Linen textiles appear to be some of the oldest in the world: their history goes back many thousands of years.
• The fine linens are used for handkerchiefs, tablecloths, and fine clothing.
• Egyptian mummies were wrapped in linen because it was seen as a symbol of light and purity, and as a display of wealth.
• In ancient Egypt, linen also was used as currency. Due to the strength of linen, paper made of it is generally very strong; due to this reason, today many countries use 25 percent linen in their currency.

Some facts about birds

• Birds (class Aves) are alike in ways that are easy to see. They cannot all fly, but they all have 2 wings. They cannot all run about on the ground, but they all have 2 legs. They all, moreover, have beaks.
• Like mammals, birds are warm blooded. Their bodies are even warmer than ours. Some birds have normal temperatures of as high as 112 degrees Fahrenheit.
• In the whole world there are about 10,000 kinds of birds. There are about 800 in the United States.
• The earliest known bird is the Late Jurassic Archaeopteryx, around 150–145 Mya (million years ago). 
• Most birds are streamlined, and they are light in weight for their size.
• Birds are light partly because many of their bones are hollow. Besides, they have tiny air sacs scattered throughout their bodies. The air sacs act like little balloons. The feathers of the birds' wings and tail are a big help in fly­ing. Their strong wing muscles are, too.
• Birds inhabit ecosystems across the world, from the Arctic to the Antarctic.
• Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich.
• An ostrich is hundreds of times as big as a scarlet tanager.
• An ostrich cannot fly.
• Most paleontologists regard birds as the only clase of dinosaurs to have survived the Cretaceous–Tertiary extinction event approximately 65.5 million years ago.
• A robín is much more like a bluebird than it is like a loon. In the same way, a hawk is much more like an eagle than it is like a woodpecker. Ways they are alike and ways they are different have been used to divide birds into groups. Among the many groups are the ducks, geese, and swans; the owls; and the parrots. Our songbirds are all in the very biggest bird group — the perching birds.
• All living species of birds have wings - the now extinct flightless Moa of New Zealand was the only exception.
• About 120–130 species of birds have become extinct as a result of human activity since the seveneenth century, and hundreds more before then.

Amphifian's world

The name amphibian comes from some Greek words which mean 'living in two places'. This is an apt descrip-tíon of the animals called the amphi­bians, as they divide their lives between water and land. Today they are all small animals, the largest being the giant salamander of the Far East, which grows to a length of about one and a half metres (five feet), but in the prehistoric past they included some which grew to three and a half metres (twelve feet) long.

Today there are about 2,000 different species of amphibians, mostly living in the warmer and damper regions of the world. They can be classified into three groups: first the caecilians or blindworms, a small tropical group of burrowing animals; second the newts and salamanders; and third, the frogs and toads.

Ligth: Wave or particle?

In the late 1600s, English physicist, sir Isaac Newton, reasoned that because light travels in straight lines and casts sharp shadows, it must behave like a tiny stream of particles. Other scientists disagreed. They argued that light traveled in waves. because it bends slightly around objects and two light beams can pass through one another. This could only happen if light traveled in waves.

The controversy ended when it was demonstrated that light displayed an interference pattern. Since only waves exhibit interference patterns, light must be waves. A hundred years later, Albert Einstein challenged this theory after studying the behavior of light striking metal objects. Einstein stated that light was tiny energy packages, or photons.

Is light composed of waves or particles? Scientists have concluded that light has the properties of both waves and particles. When it travels, light acts like a wave. When it is given off or absorbed by objects, light acts like a particle.

Some facts about the Black Death (bubonic plague)

• In the fourteenth century a fearful disease spread over Europe. It was called the Black Death. Hundreds of millions of people died of it.
• The Black Death disease originated in or near China and spread by way of the Silk Road or by ship.
• There are many stories of the Black Death. Some tell of ghost ships that drifted about with all members of the crews dead. Some tell of beggars who stole gold and jewels from the dead and became very rich — but only for a day.
• The Black Death is estimated to have killed 30 percent – 60 percent of Europe's population in the 14th century.
• It took 150 years for Europe's population to recover. 
• One of the great doctors of the Middle Ages blamed the Black Death on Jupiter, Saturn, and Mars. These three planets, he said, were too close together in the sky. Now we know that the Black Death was caused by bacteria (Yersinia pestis) which fleas carried from rats to people.
• The Black Death may have reduced the world's population from an estimated 450 million to between 350 and 375 million in 1400.
• Today Black Death is called bubonic plague. It is still terrible, but we know how to fight against it.
• Fighting it means chiefly fighting rats and fleas. In our harbors we try to keep rats from coming ashore from ships. They might be bringing in bubonic plague.
• Medieval people called the calamity of the fourteenth century either the "Great Plague" or the "Great Pestilence".
• There have been three major outbreaks of plague. The Plague of Justinian in the 6th and 7th centuries. The Black Death of the 14th century. The Third Pandemic hit China and India in the 1890s.

Monsoon season in India

A monsoon is a wind that blows in one direction for many months, up to half a year. According to a special meaning, a mon­soon refers to the southerly ocean a northeast monsoon during the winter winds that bring to India the summer season of heavy rains.

In India, the dry season comes in the winter months. Then dry cold winds blow from Sibera over India toward the Indian Ocean. As air becomes warmer, it can hold more water vapor. Since the winter winds are blowing toward warmer regions, no rain occurs. After the winter winds die down, winds begin to blow from the Indian Ocean. over India. The moisture-laden air over the ocean is cooler than the intensely-heated air over the land. The cooler air is more dense and exerts more pressure than the less dense air over the land. As the air moves over the land, it is elevated and cooled and releases its moisture as rain. In India the rainy sea­son usually lasts from June until September or October.

In winter, India lies in the northeast trade wind belt. These winds blow steadily from the northeast toward the equator. In sum­mer, the southeast trade winds prevail. The southeast trade winds (normally below the equator) shift northward in summer. Both these winds blow steadily for many months to produce the prolonged wet and dry seasons.

Interesting facts about apes

• The true apes are all larger animals with no visible tail, and with the exception of the gibbon a rather thin coat of hair.
• Men shares with apes many bodily similarities, including the same blood group system and the fact that both can catch the same diseases.
• "Ape", from Old English apa, is possibly an onomatopoetic imitation of animal chatter.
• Apes' arms are very long and strong. Their legs by comparison are small and weak.
• The hands of apes have become specialised hooks for hanging on to branches; their feet, however, have retained much flexibility and they can hold and examine objects with their big toes to a much greater extent than they can with their thumbs.
• Except for gorillas and humans, all true apes are agile climbers of trees.
• The gorilla is the largest of the apes and may weigh as much as 220 kilograms (500 pounds).
• Gorillas travel through the forests in family parties, active during the daytime and sleeping at night in nests made in the trees of woven branches.
• Gibbons are the smallest and lightest in weight of the apes and are the most highly acrobatic, swinging and leaping at very great speed through the treetops.
• Chimpanzees are much smaller and more agile than gorillas.
• Gibbons are capable of running upright on the ground or along a big branch, holding their arms out to balance themselves. They are noisy, sociable animáis, with few natural enemies in their forest home.
• The orangutan, which comes from Sumatra and Borneo, is a slow-moving heavyweight animal, keeping to the trees as much as possible, for it cannot move easily on the ground. Its food is mainly fruit and some invertebrates.
• Most nonhuman ape species are rare or endangered.
• A group of apes may be referred to as a troop or a shrewdness.

What is a mineral?

Every chemical substance which is part of the earth's crust is a mineral. Table salt, which may be mined or purified from salt water, is a mineral. Even petroleum as it comes from oil wells is classed as a mineral, as is the soft yellow material sulfur, mined in Louisiana and Texas. As can be seen from these examples, minerals may be either simple or complex substances. If a mineral is found to have only one kind of atom, it is a simple mineral element. But if a mineral is made up of two or more elements chemically united into one new substance, it is a mineral compound. To go one step further, rocks, to the geologist, are natural samples of one or more minerals, formed in the earth in a particular way. For example, calcite is crystalline calcium carbonate. But when calcium carbonate is deposited under oceans as a commonly dull, gray sediment, it is called limestone.

Minerals often form in the earth as reg­ular shapes called crystals. Examples of common crystalline minerals are fluorite, galena, pyrites, calcite, and quartz. Many of the crystalline minerals are used for jewelry because they are scarce or fashionable, brilliant in luster, clear and transparent, beautiful in color, or very hard and long lasting.

The diamond is an example of a valuable and beautiful mineral. It is the hardest known mineral. Thus it can be cut only with other diamonds. Ancient stonecutters found that by cutting and polishing a diamond in a certain way, ligth could be made to bounce from several sides inside the diamond before it reflected back to the eye,
giving the typical sparkle. Other precious minerals are sapphire, emerald, and ruby.

How Does a Camera Work?

old camera

There are amazing pictures of Newton, George Washington, Beethoven, and other famous men of earlier times. But these pictures are paintings, not photographs. Photographs became possible only a little more than one-hundred years ago after the camera was invented.

A camera is a light-tight box. Light can come into it only when a shutter is pulled away from a small opening at the front. Then the light shines in through a lens in the opening. The lens throws a picture of what is in front of it on a film or a plate at the back of the box. This film or plate is coated with a chemical sensitive to light.

Fortunately a camera lens can throw on a plate or film a small picture of a very large object. Otherwise, we could not take pictures of big buildings or clouds or crowds of people. After a picture is taken, the plate or film has to be developed.

A camera may cost only a few dollars or it may cost hundreds of dollars. One big difference between a cheap camera and an expensive one is in the quality of the lens. The best lenses are very expensive because they are very carefully ground.

Moving picture cameras are much like other cameras. They simply take one pic­ture after another very rapidly.

Some facts about wine

• Wine is an alcoholic beverage that can be made from several fruits, vegetables and flowers, but the most notable plant in wine making is the grapevine.
• The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients.
• The great wine grapes belong particularly to the regions where the famous wines are made. Such grapes are the black Cabernet Sauvignon of Bordeaux, and the black and white Pinot of Burgundy and Champagne, all three districts of France; the Riesling of the Rivers Rhine and Moselle; the Pedro Ximenez of Jerez in Spain; and the Furmint of Tokay in Hungary.
• All these wine-growing regions have developed their own particular grapes which produce wines distinctive to each district.
• An expert taster can tell not only where a wine comes from but often the year in which it was made.
• Different varieties of grapes and strains of yeasts produce different types of wine.
• When grapes are crushed, the juice can be run off at once for the making of white wine, or it can be left to ferment in the presence of the stalks, skins and pips of the grapes to make red wine.
• A pink or rose wine can be produced by allowing the juice to ferment for a short while with the skins of the grapes, which contain the colouring matter.
• All the colouring of table wines comes from the skins of the grapes and has nothing to do with the colour of the growing fruit.
• The commercial use of the word "wine" (and its equivalent in other languages) is protected by law in many jurisdictions.
• The English word "wine" comes from the Proto-Germanic "winam," an early borrowing from the Latin vinum, "wine" or "(grape) vine,"
• Wine has also played an important role in religion throughout history. The Greek god Dionysus and the Roman equivalent Bacchus represented wine, and the drink is also used in Christian Eucharist ceremonies and the Jewish Kiddush.

Some facts about the kidneys

• The kidneys are organs which function to rid the body of some of its waste materials.
• The human body has 2 kidneys. They are shaped like large beans.
• Despite their relatively small size, the kidneys receive approximately twenty percent of the cardiac output.
• The right kidney is slightly lower and smaller than the left one.
• The kidneys serve the body as a natural filter of the blood.
• The kidneys are embedded in fatty tissues which protect the organs.
• The kidneys act as a filter system which collects and rids the body of many of its waste materials. The formation of urine depends upon the action of the kidneys.
• Calcitriol, renin, and erythropoietin hormones are produced in the kidneys.
• Each adult kidney weighs between 125 and 170 grams in males and between 115 and 155 grams in females.
• Common clinical conditions involving the kidney include the nephritic and nephrotic syndromes, nephrolithiasis, chronic kidney disease, renal cysts, urinary tract infection, acute kidney injury, and urinary tract obstruction.

Facts about Athletics

Usain Bolt

The term athletics is derived from the Greek word "athlos", meaning "task" or "contest."

More than 2,000 years ago the Greeks said that it was just as wise to train the body as to train the mind.

Athletic events involve competitive jumping, running, throwing, and walking.

In much of North America, athletics is synonymous with athletic sports in general.

Almost every high school and college in the United States has its baseball and basketball teams. Many have football and tennis teams.

All over the United States mere are track and field rneets every year. These meets are contests in running, jumping, pole vaulting, and throwing. There are swimming meets, too.

In athletic meets careful records are kept. Every once in a while a newspaper headline tells that some record has been broken.

Organised athletics are traced back to the Ancient Olympic Games from 776 BC.

The simplicity of the competitions makes athletics one of the most commonly competed sports in the world.

Some facts about rockets

Space Shuttle

1. The Chinese invented the rocket around a.d. 1150.
2. The ancient Chínese developed fireworks for religious festivals.
3. Beginning in the 13th century, the Chínese used rockets extensively. The rockets burned an explosive black powder that propelled them into the air.
4. Rockets are used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight and space exploration.
5. All rockets require fuel that produces rapidly expanding gases. The force of the escaping gases thrusts the rocket forward.
6. Significant scientific, interplanetary and industrial use of rockets did not occur until the twentieth century, when rocketry was the enabling technology of the Space Age, including setting foot on the Moon.
7. Rocket fuels became very important as space exploration and technology developed.
8. Liquid rocket engines use a liquid oxidizer and a liquid fuel. Theses propellants are usually pumped up then mixed together and burned in the engine's combustion chamber.
9. Modern space rockets also use solid fuels, which when mixed together, release oxygen and burn.

Do all plants use photosynthesis?

Not all plants use photosynthesis to create the proteins of their food supply. Instead, they live off other plants and animals, working in the darkness. Some can even be killed by too much exposure to light. Such plants are the bacteria and the fungí. They are nature's rubbish disposal operatives.

A study of bacteria and fungí may one day lead us to solve the two great mysteries of how life began in the sea and how plants first invaded the land. Some species of bacteria are able to build up protoplasm, the living matter of a cell, from carbon dioxide and chemical salts by a process called chemosynthesis. This is similar to photosynthesis, but takes place in the absence of light. Such bacteria may be not unlike the primitive forms of life first produced on earth.

Fungi, on the other hand, in their structure and behaviour resemble seaweeds and may be a development from the first plants to climb ashore and adapt themselves to life on the land. The question of which carne first, the photosynthesising green plants or the seaweed-like fungí that learned to live off them, remains unanswered.

Some facts about Light

• Dutch astronomer, Christian Huygens, (1629–1695) stated that light was vibrations or waves which spread everywhere through a space-substance called ether.
• By 1864 James Clark Maxwell stated that light waves were electromagnetic waves.
• The quantum theory states that light may behave as both particles and waves.
• Light from an object must reach the eye to be seen. 
• Most objects are visible be­cause they reflect light from a luminescent or glowing source.
• Life is dependent upon light. Without the trapping and storing by chlorophyll in living plants of light energy, there would no chain of life.
• The Sun is the main source of "nat­ural" light.
• A light year is the total distance that light will travel in one year.
• Materials which are heated to above 1400 °F (800 °C) produce light. 
• Solids and liquids are then incandescent (glowing with heat).
• Some objects are luminescent without it being necessary for them to be at high tem­peratures. 
• Certain chemicals when mixed together give off light called chemiluminescence.
• A firefly's tail produces a "cool" light.
• A gas through which an electric current passes will emit light that is not incandes­cent.
• The brightness and color of light will not vary from gaseous materials, but depend upon the nature of the gas.

Interesting facts about Attila

Attila the Hun

• In 433 Attila and his brother Bleda became joint rulers of the Huns.
• Eleven years later Attila had Bleda killed.
• The Hunnic Empire stretched from the Ural River to the Rhine River and from the Danube River to the Baltic Sea.
• At the age of 12, he was sent as a child hostage to the Roman Court and in return, the Romans sent Flavius Aetius to the Huns.
• Attila was so cruel a warrior that he was known as the "scourge of God"
• Attila the Hun crossed the Danube twice and plundered the Balkans, but was unable to take Constantinople.
• In 453, Attila the Hun married a young barbarian princess, Ildico.
• In 453 Attila was preparing to march on Italy. But suddenly, just before his troops were ready to set out, he died.
•  The body of Attila was put in a coffin of gold. The gold coffin was put in a coffin of silver. The sílver coffin was put in a coffin of iron.
•  Men were sent to bury Attila. When they carne back they were killed. No one must ever know Attila's burial place!
• The origin of Attila's name is unclear. Pritsak considers it to mean "universal ruler" in a Turkic language related to Danube Bulgarian.

Ancient ideas about motion

More than two thousand years ago, Chinese philosophers wrote about motion in a book called the Mo Ching. They wrote: "Motion stops due to an opposing force. If there is no opposing force, the motion will never stop."

In ancient Greece, Aristotle wrote that horizontal motion was "unnatural." He thought that a push or a pull was needed to start and to keep something in horizontal motion. He aiso thought heavy objects fall at a faster rate, or acceleration, than lighter objects do. Aristotle's ideas about motion were widely accepted for more than 1,900 years.

During sixteenth century, Galileo questioned the ideas of Aristotle. He reasoned that if two bricks of the same mass fall at the same rate, side-by-side, they ought to fall at the same rate even when cemented rogether. In 1589, according to an often-repeated, unverified story, Galileo did an experiment from the Leaning Tower in Pisa, Italy. Galileo is supposed to have dropped two cannonballs of different masses at the same time from the top of the tower. Both cannonballs reached the ground at about the same time. Whether he actually did the experiment or not, his reasoning was correct.

Galileo Galilei also did experiments that showed that an object moving horizontally continues to move at the same speed unless a force opposes it. Galileo's experiments confirmed the ideas stated thousands of years earlier in the Mo Ching book.

The art of Falconry

Falconry, the art of catching game with birds of prey, was first practised in the Far East before 1000 B.C. Introduced into Europe in the ninth century it was, until the invention of guns for shooting birds, the chief sport of the aristocracy. Almost all sorts of birds of prey have been used, from eagles to male sparrowhawks. The birds to be used for falconry must be taken from the nest shortly before they are able to fly. Taming the falcon is a Job requiring skill and dedication and since the bird needs to be flown fairly frequently, should only be attempted by someone with plenty of time to give to it. The trained bird wears a hood which covers its eyes and prevenís it from becoming frightened by strange sights and sounds, but can be removed very quickly if it is to be flown. At all times the hawk carries small bells on its legs. These enable the falconer to hear where the bird is if it hides in dense trees while being flown, and to keep an ear on its welfare while the bird is confined in its cage, which is called a mew.

Useful bacteria

Bacteria have a nasty reputation because of their association with some of the illness that afflict people. Yet without them nature would not persist to produce the rich variety of life on which we all depend. Bacteria are
microscopic in size and multiply rapidly, one producing as many as 16 million others in a single day.

Under the microscope, bacteria are seen to be transparent cells usually without colour. They consist of a mass of protoplasm encircled by a wall which is somewhat different from the cell wall of higher plants. Bacterial cells do not seem to include an organised nucleus. The cells hold food reserves, grow rapidly and divide almost immediately they have reached their full size. After división, they may split, cling together in chains or irregular masses or form a series of branches. In extremes of temperature, bacteria form thick-walled spores called endospores which remain until conditions for growth again become propitious.

Bacteria live in or on animals or plants. They secrete enzymes, lifeless substances made out of living matter, which help to break down the tissues of their hosts to feed bacterial growth. When bacteria live as parasites, they harm the host plant or animal and sometimes kill it. In the soil, they extract nitrogen from the air and convert it into nitrates which help to feed plants. When bacteria are thus beneficial to their hosts, they are said to be symbiotic, which means living in partnership. Bacteria that live on and decompose the waste matter of plants and animals are saprophytes.

Among the things for which bac­teria are useful to man are separating the fibres of such plants as flax, jute and hemp for making cloth and rope, turning animal dung into nitrate-rich manure, converting wine into vinegar and milk into cream for butter, in the curing of tobacco, and the tanning of leather.

Liquids in nature

Liquids are necessary for both plants and animals. Both blood, which is a liquid, and sap, another liquid, carry nourishment through the bodies of animals and through the stems and leaves of plants. Without this
nouris­hment they would die.

Without liquids there would be no oceans, no running brooks, no lakes and no rain.

All matter has three conditions. It may be a gas, it may take the form of a solid, or, finally, it may be a flowing liquid.

Those who have seen water turn to ice or have watched steam pour from a kettle know that matter which is normally liquid may become either a solid or a gas. However, matter is called liquid if that is its normal form under ordinary conditions of temperature. In many cases, also, conditions of pressure may change liquid to
another form.

Modern day scientists have even been able to make normally solid matter assume liquid form. Such is the case in some of the new processes for turning coal into liquid, at normal temperatures.

The small "pieces" which go together to form all matter are known as molecules. These are held together by an action called cohesion. Cohesion is strongest in solids; the greater the cohesion the more "solid" the matter.
Liquids are "liquid" because their cohe­sión is less. Their molecules can move about to a greater degree than in solids, and so they flow into a container and take its form.

What is the Aurora Borealis?

For a long time the northern lights (aurora borealis) were a great puzzle. The people of olden times made up many stories to explain them. One of these was that the light came from a battle the gods were fighting. In more re­cent times people have thought the aurora was sunlight reflected from the snow and ice in the Far North.

The right explanation. scientists tell us, is this: On the Sun there are often great storms. We call them sunspots. From these sunspots, streams of tiny electric particles are shot out. When these particles reach the upper air, they cause the aurora. The different colors come from the effect of the electric particles on the different gases in the air. The colors are produced very much as colors are produced in neon signs.

The northern lights are at their best in the Far North. But they have been seen from all over the United States and Europe.

In the Far South there are lights like the northern lights. They are called the aurora australis.

Interesting facts about Johann Sebastian Bach

• German composer, Johann Sebastian Bach was born on March 21, 1685.
• Bach was born in Eisenach, Germany.
• Music as we know it today began with Johann Sebastian Bach.
• Bach taught many of his 20 children to play musical instruments. He composed the Little Book for the Keyboard for his nine-year-old son, William Friedemann.
• Bach ranks as one of the world's greatest composers. Most of his music was written to be played or sung in churches.
• Many of Bach relatives were musical. Once each year the Bachs held what they called "family day." For the whole day they all sang, danced, and played instruments.
• Before Johann was ten years oíd his parents died, and he went to live with an older brother.
• Once his brother refused to let him use a big book of difficult music. Johann then took the book secretly and copied all the music by moonlight. The strain on his eyes may help account for his blindness towards the end of his life.
• Bach began to earn his living when he was 15. He sang in a church choir. Before long he was given a position as organist. He became the greatest organist who had ever lived.
• In 1707 Johann married his second cousin, Maria Barbara Bach. She bore him seven children, four of whom survived him.
• After his first wife died, Bach married Anna Magdalena, they had thirteen children, only six of whom survived him.
• In Bach's time he was famous as an or­ganist, not as a composer.
• It was not until 1829, almost 80 years after his death, when Mendelssohn led a performance of the St. Matthew Passion, that Bach's music was accorded the recognition it deserved.

Something about leather

Leather Animal hides that have been chemically treated to soften and pre­serve them are called leathers. Shoes, belts, luggage, handbags, gloves, etc. are made of leather.

Leather can be made from the hides. of such animals as cattle, sheep, lambs, goats, reptiles, horses, sharks, and ostriches. Cattle hide is most generally used. Tanning is the chemical treatment of the inner layer of skin to convert hides into leather.

At the tannery the hides are washed and soaked to remove the salt and to restore the fibers to their natural shape and condition so they will absorb the tanning agents easily. The hides are soaked in a lime solution or in an enzyme preparation to loosen the hair. Then they are put through a dehairing machine. The hides then are placed in a "paddle pit" with warm water, an enzyme and a lime neutralizing agent. After neutralization, they are washed with cold water and drained, then dried.

Asteroids in the Solar System

The term "asteroid" means "starlike," but asteroids are actually little planets. They travel around the Sun just as the big planets do. The paths of most of them are between the paths of Jupiter and Mars.

Ceres, the largest asteroid known, is 480 miles (772 km) in diameter. Eros is 18 miles (29 km) in diam­eter. Amor is only about a mile across. They are all too small to hold any air on them. They do not have enough gravity. There is so little gravity on Amor that, if a person could go there and could take a train with him, he could lift the train with one hand and swing it around his head.

About 1,500 asteroids have been discovered. New ones keep being found. Of course, these new ones are not really new. They have simply never been seen before. None of them can be seen without telescopes. Most of them have been discovered in pictures taken through telescopes.

The asteroid Kermes made a name for itself in 1937. It carne very close to the earth on one of its trips around the Sun. It was only 621,000 miles away!

No one knows surely how the asteroids were formed. One guess is that they came from a large planet which was once between Mars and Júpiter. Perhaps the large planet came too close to the giant Júpiter and was pulled to pieces.

Sometimes asteroids are called planetoids. Planetoids is really a better name, for these small bodies do not shine by their own light as stars do.

Walking stick facts

• The walking stick (Phasmatodea) is an insect that looks like a twig without leaves.
• Their natural camouflage can make them extremely difficult to spot.
• The walking stick's body is thin and its three pairs of legs are long and awkward.
• Phasmatodea can be found all over the world in warmer zones, especially the tropics and subtropics.
• The walking stick in the U.S. has no wings. It is a tree insect with a greenish-gray or brown color that makes it look like a twig when it not moving.
• Females of the genus Phobaeticus are the world's longest insects, measuring up to 56.7 centimetres (22.3 in) in total length in the case of Phobaeticus chani, including the outstretched legs.
• The shape and color of the walking stick help protect it from its enemies. This kind of color is called protective coloration.
• Depending on what the trees are like in their native habitat, walking sticks will look like a twig or branch from that tree.
• The walking stick moves so slowly that hardly seems alive.
• All walking sticks are herbivores.
• Because the walking stick cannot bite, sting or move quickly, it depends on its ability to look like a stick to escape its enemies
• Some walking sticks have bark-like markings and even feel like a twig. If a walking stick is caught by a leg, it can break the leg off and escape. This form of protection by means of self-amputation is called autotomy.

The game of bowling

The popular game of bowling is played with big pins and a big ball. Ten wooden pins weighing at least 3½ pounds apiece are set up at one end of a smooth runway, or alley. The balls may weigh as much as 16 pounds (7 kg) and be 27 inches (69 cm) around. A player who finds a 16-pound ball too heavy may use a lighter one. But, of course, with a heavy ball a player has a better chance of knocking down the heavy pins.

There are ten rounds, or frames, in a game. In a frame each player is allowed to roll two balls. If he knocks all the pins down with the first ball, he has a "strike." If he knocks them all down with two balls, he has a "spare."
Scoring is rather complicated. The highest possible score in a game is 300. To get this the player must have a strike in every frame. Perfect games are not common, but neither are they rare.

Bowling was brought to the United States by early Dutch settlers. It was then called "skittles" and was played with nine pins instead of ten. The lawmakers thought that people were wasting too much time playing ninepins and passed a law against the game. But those who wanted to play soon found a way of getting around the law. They began using ten pins instead of nine.

The marsupial world

The word Marsupium means "pouch" or "bag." Included in this interesting group of animals are the great gray kangaroos, the small kangaroos or wallabies, the opossums, the Tasmanian wolf, and the furry koala bear. At one time, these animals were found all over the world. Now, most of them live in Australia and on nearby is-lands. While a few species live in South America, none are found in Europe, Asia, and África. The only species living in North America is the Virginia opossum.

Since all marsupials are mammals, the females nourish their young on milk from their own bodies. Marsupials are diíferent from other mammals, since their young are born small in size and underdeveloped in most ways. These young animals are really embryos which look somewhat like baby birds taken from their shells before they are ready to hatch.

After birth, the young marsupials scramble through the hair on the mother's body. Without the mother's assistance, they climb up to the pouch by clawing with their limbs. In the pouch, they cling so tightly to a nipple that it is difficult to remove them. After they have been weaned and are able to obtain their own food, they often cling to the fur of the mother's back and ride about for protection. The kangaroo allows the young to hide in its pocket, in the event of danger.

Not all female marsupials have pouches. The banded anteater, for example, carriés its young on the bottom of its body. Since they cling to the nipples, without protection, the mother must elevate its hind legs to prevent the young from being dragged off.

Facts about ruby-throated hummingbirds

• Ruby-throated hummingbirds are very tiny. They are only three inches (7–8 cm)  long with an 8–11 cm wingspan.
• Their beaks are almost half as long as the rest of their bodies.
• The Archilochus colubris is the only species of hummingbird that regularly nests east of the Mississippi River in North America.
• With their long beaks and tongues ruby-throated hummingbirds are able to get the sweet nectar from deep down in flowers. 
• The species is dimorphic.
• The male is smaller than the female, and has a slightly shorter beak.
• Ruby-throated hummingbirds can fly forward, backward, or straight up and down. By keeping their wings moving very fast, they can also poise ín mid-air. 
• Muscles make up 25-30% of their body weight.
• Their feet are frail and are used only for perching on fine twigs. These tiny birds never run or even walk.
• Ruby-throated hummingbirds build very firm cup-shaped nests out of plant down and other soft materials. 
• Nectar from flowers and flowering trees, as well as small insects and spiders, are its main food.
• The mother hummingbird lays two white eggs which are no larger than peas.

Interesting facts about Wallabies

• Wallabies (Family Macropodidae) are medium-size, shy kangaroos. Like all kangaroos, they have large, strong hing legs, a thick long tail, and carry their young in a pouch.
• The name wallaby comes from the Eora Aboriginal tribe who were the original inhabitants of the Sydney area. 
• Wallabies are native to Australia.
• Wallabies also can be found at the island of New Guinea.
• Young wallabies are known as "joeys", like many other marsupials.
• Most wallabies feed at night on grass and leaves. Their speed and dodging ability make them very hard to see or to catch. Thus they are protected from their enemies—the dingo, rock python, eagle, and man.
• New Guinea, which was until fairly recent geological times part of mainland Australia, has at least five species of wallaby.
• The hare wallaby is the size of a large rabbit, while the colorful red-necked wallaby may be almost four feet long.
•  Rock walla­bies, not much bigger than house cats, leap fearlessly among the crevices and chasms of rocky cliffs.
• The small, graceful nail-tail, or spur wallaby, has a thorny growth on the end of its tail and lives in desert land.

Facts about birds of prey

• Many species of birds feed on flesh, but 2 groups—the birds of prey and the owls—have become highly specialised in a hunting way of life, and feed mainly on the higher vertebrates.
• Birds of prey are found on all the continents except Antarctica.
• Birds of prey are birds that hunt for food mainly on the wing, using their sharp senses, especially vision.
• These birds kill their prey with their strong, sharp talons and pluck and tear the flesh with their narrow, hooked beaks.
• Most birds of prey also eat carrion at least occasionally and the vultures and condors eat carrion as their main food source.
• Birds of prey and owls can exist in the same area together since they are active at different times, the birds of prey during daylight hours and the owls at night.
• The word "raptor" is derived from the Latin word rapere (meaning to seize or take by force) and may refer informally to all birds of prey, or specifically to the diurnal group.
• Although their eyesight is excellent and adapted to make the best use of poor light, owls also have a highly developed sense of hearing.
• Under experimental conditions it was discovered that a barn owl could catch its prey in total darkness, using its ears to judge the distance perfectly.
• The smallest bird of prey is the Philippine falconet, which is only about 15 cm (6 inches) long and eats insects; the largest is the Andean condor, with a wingspan of nearly 3 m (10 feet), which feeds mainly on carrion.
• All the birds of prey are active hunters, but their methods vary considerably.
• Most birds of prey have strong curved talons for catching or killing prey.
• The eagles, which are powerful soaring birds, live mainly in open country and mountains.
• The golden eagle hunts mainly rabbits, mountain hares, grouse and very occasionally a sickly lamb.
• The true hawks are broad-winged, long-tailed birds, adapted to life in woodlands where they stalk and pounce on their prey.
• The most spectacular of the birds of prey are the falcons.
• Because of their gracefully controlled flight and their apparent courage, the birds of prey have always appealed to man.

What is a magnet?

horseshoe magnet

A magnet is a object which has the property of attracting certain ferromagnetic materials such as iron and steel. If a magnet is suspended on a string or fine wire, it will turn until it aligns itself in a north-south direction.

Mankind has known about magnetism for centuries. There is evidence that the first natural magnets were found in a place in Asia Minor called Magnesia. These natural mag­nets consist of an oxide of iron called magnetite. When this ore is found in the magnetized state, it is given the name "lodestone," (leading stone). The properties of magnetite were first investigated by the English physician, William Gilbert, whose famous trea-tise "De Magnete" appeared around the year 1600.

Interesting facts about mammoths

• The ancient mammoth was a relative of the modern elephant.
• One name of the mammoth is Elephas primigenius, which means "first-born elephant."
• The mammoth is now extinct and is found only as a fossil.
• Mammoths lived from the Pliocene Epoch from around 4.8 million years ago, into the Pleistocene at about 4,500 years ago.
• Cave drawings by the CroMagnon men 10,000 years ago show that the mammoth was hunted for its meat.
• The word mammoth comes from the Russian мамонт mamont, probably in turn from the Vogul (Mansi) language, mang ont, meaning "earth horn".
• Steppe mammoth evolved into woolly mammoth
• Most of the characteristics of the mammoth were identical to the modern Indian elephant, One difference was its thick, dark brown hair, sometimes two feet long.
• In English language the noun "mammoth" has become an adjective meaning "large" or "massive".
• The mammoth also had short, furry ears and a special spiral to the tusks that modern elephants do not have.
• Woolly mammoths traveled into North America via the land bridge (Central Beringia) ~1.8 mya
• In January 2011, a team of scientists headed by Akira Iritani of Kyoto University, say they will extract DNA from a mammoth carcass that had been preserved in a Russian laboratory and insert it into the egg cells of an African elephant in hopes of producing a mammoth embryo. The researchers said they hoped to produce a baby mammoth within six years.

Facts about Guglielmo Marconi

• Guglielmo Mar­coni was the inventor of wireless telegraphy.
• The Titanic disaster in 1912 gave the wireless even more fame. Those who survived were rescued by ships that had received the wireless call of the sinking ship.
• Guglielmo Marconi was born on 25 April 1874, in Bologna, Italy, of an Italian father and an Irish mother.
• When Marconi was 16, he successfully proved his theory that an electric current can pass through most substances without difficulty.
• Guglielmo Marconi was only 20 years old when he had his great idea for sending signals with electrical waves.
• Marconi won the Nobel Prize for Physics (1909) and many other honors.
• As early as 1922, Marconi anticipated the development of radar. He found that radio waves were reflected from metal objects, and suggested that they could be used to detect the presence of ships in fog even if those ships did not have radio.
• Guglielmo Marconi invented tuning, which made it possible to have many different stations without their interfering with each other. The famous British Patent No. 7777 was granted for this tuning system.
• Marconi died on 20 July 1937 (aged 63)

The importance of machines

The use of machines has enabled man to do work that he lacks the power to do unaided. Ma­chines have also made it possible for him to harness the forces in the wind, in fuels, and in water. Without ma­chines man would still exist in a primitive state and the progress he has made could never have come about. A machine is any device used to increase force, change the direction of force, or increase speed in performing work. Work is done only if something is moved by overcoming a resistance, such as friction or gravity. A simple machine has no energy source within it, so it cannot do work unless work is put into it.

Where friction causes only negligible loss of energy, work produced by a machine equals the amount of work put into it. This work of machines is measurable. It is the product of the unit of force and distance. For example, if a person lifts a ten pound box three feet, he has done three times ten pounds or thirty foot-pounds of work.
The mechanical advantage of a machine is the ratio of resistance to effort. For example, a man lifts fifty pounds of weight by applying ten pounds of effort to a lever. Then the mechanical advantage of the lever is five to one.

Where does Asphalt Come from?

In paving a street men often use a black, tarlike ma­terial. The material is asphalt. Asphalt is also used in the making of roofing paper, shingles, tiles for flooring, and paints.

Asphalt is found in places where there is or used to be petroleum. It may flow slowly out of the ground and collect in pools. The asphalt that comes from the ground is called natural asphalt. Asphalt can also be made from petroleum.

When asphalt stands, it changes from a thick liquid to a soft solid. Chunks of as­phalt are often found floating on the Dead Sea. In early times much asphalt was mined near this sea. Farther north. in Mesopotamia, the land between the Tigris and Euphrates rivers, there were many as­phalt springs, too. The people in that región long ago cemented bricks together with as­phalt to make pavements. They also sealed jars with asphalt.

The famous tar pits of California are pools of asphalt. In these pools scientists have found many wonderful fossils of mammoths, sabertooths, vultures, and other animals of the great Ice Age. So many fossils have been found in these pools that sometimes they are called "the deathtrap tar pools."

It is not hard to see how the deathtraps worked. After a rain, water covered the asphalt. Animals that waded out to get a drink became caught in the sticky substance and began to sink. Meat eaters—wolves and sabertooths—saw them and sprang on them. Then the meat eaters were caught, too.

Facts about magpies

Magpies (Corvidae) are slender, bold birds about 20 inches (51 cm) in lenght.

Magpies live in groups of 5 to 12 in the western part of the U.S.

Magpies are able to imitate the calls of other birds.

That bird was referred to as a "pie" until the late Sixteenth century when the feminine name "mag" was added to the beginning

Magpies have white and glossy green-black feathers.

Magpies are believed to be one of the most intelligent of all animals: the European Magpie is one of the few animal species known to be able to recognize itself in a mirror test.

The mother magpie lays from 5 to 10 green eggs which are spotted with brown and purple.

Magpies eat insects, berries, fruit, carrion, and the eggs and youg of other birds.

Magpies belong to the same family as the crow, jay, and blackbird.

Cathedrals of the Middle Ages

The Middle Ages are sometimes called the Age of Faith. To show their faith in God, the people of those times built great churches called cathedrals.

During the Middle Ages the common people were poor. Many of them lived in houses that we would call hovels. But their poor houses did not matter so much if they had beautiful churches to worship in.

It took more than 100 years to build some of the great cathedrals. The people of a region did not simply hire someone to build their great church for them. Instead, they did much of the work themselves. No people worked harder for their cathedral than did the people of Chartres in France. Princes and peasants, old men and boys, hitched themselves to carts as if they were horses and pulled loads of stone.

The cathedral of Chartres towers high above the town. It is in the style of architecture called Gothic. The main part of the ca­thedral is in the form of a cross. The arches are pointed. Great braces called flying buttresses strengthen the thick walls of stone.

Magnificent stained glass Windows and hundreds of figures carved from stone help make the cathedral beautiful. The higharched ceiling and the soft light coming through the stained glass Windows make the inside of the cathedral aweinspiring and give an air of mystery.

A cathedral of the Middle Ages was the center of the life of the town. The people for miles around gathered there to worship. They carm for Christmas and other special celebrations. At times there were plays that told stories of the lives of saints.

What is Me­tabolism?

Me­tabolism is the process by which living things grow and repair their bodies and produce energy needed for life. Metabolism includes all the chemical changes that take place in the protoplasm of the cell. The changes which build up new protoplasm from simpler materials are called anabolic metab­olism. The changes which break down parts of the protoplasm are catabolic metabolism.

All metabolic processes use food as the raw material for supplying energy and building new tissues. Foods include water, minerals, vitamins, carbohydrates (starches and sugars), proteins, and fats. The latter three are changed by digestion to simple sugar, amino acids, fatty acids, and glycogen, which can be assimilated. Glucose, fats and amino acids may be used to form a basic part of protoplasm, oxidized to give the body the heat and energy it needs, or stored for future use.

The first submarine cables

The first telegraph line was opened in 1844. Soon there were thousands of miles of telegraph lines on land. And before long people could send telegraph messages across oceans. Sending these messages was made possible by the laying of heavy wires, or cables, across the seas from continent to continent. Ca­bles laid under the sea are called submarine cables. The telegraph messages sent over them are called cablegrams.

The Atlantic was the first ocean to be crossed by cable. After several failures, Cyrus W. Field, an American, succeeded in 1866 in laying a cable from Newfound-land to Ireland. The Pacific Ocean was spanned with a cable 36 years later.

In 1955 a telephone cable was laid across the Atlantic. Since then other telephone cables have been laid. Such cables make it possible to hear someone across the sea as clearly as if he were just across town.

The wire through which the electricity flows is only a small part of a submarine cable. The wire must have waterproof covering, because salt water is a fairly good conductor of electricity. The wire must be protected against sharp rocks, dragging anchors, and swordfish. The cable must be so strong that it will not break of its own weight as it is being lowered to its place at the bottom of the sea. The cable also must have an outside layer that shipworms cannot bore through.

Something about building materials

bricks

In some parts of the world there are few materials to build with. Snow, driftwood, walrus skin, and sod, for instance, are about all an Eskimo can find for building. But in the United States and many other countries, too, there are numerous materi­als to choose from. We can choose from more than a dozen materials for the outside walls. Many other materials can be used for roofs and floors and inside walls, for pipes and gutters and built-in furniture.

Stone is a natural building material. It has only to be cut into the shape wanted. There are dozens of kinds of stone. Those used most in building are limestone, marble, granite, sandstone, and slate. Sometimes the stone is not even cut into shape. Rounded stones called field stones make attractive walls.

Wood is another natural building mate­rial. There are many kinds of wood to choose from. Fine and oak are common.

Interesting facts about Alessandro Volta

Alessandro Volta was an Italian physicist who was a pioneer in electrical discovery.

Full name: Alessandro Giuseppe Antonio Anastasio Volta

He was born in Como, Italy, on February 18, 1745.

Volta is especially known for inventing the first true battery in 1800.

Volta invented the electrophorus, an apparatus used in generating static electricity, and the electroscope, which could detect small charges of electricity and tell whether a charge was positive or negative.

Alessandro Volta also invented an electrostatic pistol and the electrical condenser.

Volta discovered methane by collecting the gas from marshes.

In 1794, Alessandro Volta married Teresa Peregrini, with whom he raised 3 sons, Giovanni, Flaminio and Zanino.

Volta's work was appreciated almost immediately, not only by his fellow scientists, but also by the political heads of state. In 1801 Napoleón called him to París, and a special gold medal was given him.

Calories in food

high calorie food

No one can live long without food. One reason why is that our bodies must have fuel. The foods we eat serve as fuel. They burn slowly in our bodies and furnish the heat and energy we need to keep us alive. The fuel value of a food is measured in calories. The word "calorie" comes from the Latin word meaning "heat."

Some foods furnish much more heat and energy than other foods do. The fuel value of a slice of watermelon, for instance, is only about 100 calories. But the fuel value of a piece of chocolate meringue pie is about 450 calories.

Boys and girls use up so much energy that they need a great deal of fuel food. If they are from 9 to 12 years old, they need about 2,500 calories a day. If they do not get that many, some of their body f at burns up. If there is no fat, some of their body cells burn up instead.

Foods that furnish the most calories are not always the best for us. We must think not only of calories, but of other things, too, in choosing what we eat.

Tree bark

tree bark

Every tree has its own kind of bark. The bark of a paper birch is smooth and white. The bark of a hickory tree is dark and shaggy. The bark of a sycamore has patches of brown and white. But bark, no matter how it looks, always helps a tree in the same ways.

The outer layer of bark is made of cork, which is waterproof. This layer is a protection against injury from animals and against drying winds. The inner layer of bark can be hurt easily and needs protection. It plays an important part in the life of the tree, for it is made up partly of tubes, called "sieve tubes," that carry food for the tree. Just inside the bark is another región that needs protection. It is the región where new wood is formed. In the new wood water travels up from the roots to the treetop.

Once in a while lightning strikes a tree and peels off all its bark. The tree then has no chance at all of living.
The indians used to make canoes of birchbark. Bark can be used in building other things. too. Several drugs come from bark. One of them is quinine. The spice cinnamon comes from the bark of the cin­namon tree.

Tannin used in making leather comes from the bark of oak trees. Cork comes from the bark of the cork oak. Bark helps people as well as the trees it grows on.

Something about camouflage

The spider crab has no good weapons for protecting itself. But it has a good way of hiding from its enemies. It plants tiny seaweeds and little animals of the sea on its back and on its long legs. They make it match its surroundings. When a spider crab travels to a new place it may change the plants and animals on its back.

The decorations of the spider crab are a kind of camouflage. Camouflaging anything means making it look so much like its surroundings that it is hard to see.

There are many examples of cam­ouflage in nature. From all these examples people have learned a great deal about camouflage.

Metric system

scThe metric system was established in 1790 by a group of scientists in France. It works by a simple decimal, or ten, system, using only three basic units. The main measurements are the meter (length), the gram (mass), and the liter (capacity).

There are ten prefixes which can be attached to any of the units. Each subdivides or multiplies the basic unit by ten:
mega means 1,000,000
myria means 10,000
kilo means 1,000
hecto means 100
deka means 10
deci means 1/10
centi means 1/100
milli means 1/1000
micro means 1/1,000,000
millimicro means 1/1,000,000,000

What is leukemia?

acute leukemia

Leukemia describes a number of disorders of blood-forming tissues, in which the white blood cells steadily increase. The white blood cells crowd out the red blood cells and platelets so that the person cannot get enough oxygen and bleeds easily. The cause of leukemia is unknown, although there is a possibility that an obscure virus is involved.

In leukemia these new cells become increasingly numerous and are found in all body tissues. This abnormal production of cells changes the content of the blood. In some patients the disease progresses slowly; this is chronic leukemia. In other patients the cells are poorly formed and more quickly produced; this is acate leukemia. Chronic leukemia usually occurs between twenty and forty years of age. Acute leukemia occurs more frequently in people under twenty-five years of age.

The victims have loss of appetite, loss of weight, a slight temperature, bone pain and mild anemia. They are weak, pale and usually tire easily. The spleen and often the liver are enlarged.

The physician depends on laboratory findings for diagnosis. Samples of bone marrow and blood are examined. In leu­kemia these samples contain an abnormal number of white cells and a reduced num­ber of red cells and platelets that are immature and imperfectly formed.

What are simple machines?

There are machines of all kinds and sizes in existence today, but no matter how complex they may appear, all machines are a combination of several simple machines or modifications of one. A simple machine is one that is moved by just one force. There are six such machines: the lever, wheel and axle, pulley, inclined plane, screw, and wedge.

The lever is a long plank, beam, or bar that is used to move heavy loads. Archimedes, a Greek mathematician, discovered the law of the lever and stated that if he were given a long enough stick and a place to stand, he could move the world. The beam rests on a firm object called the fulcrum. The point of resistance is the place where the load to be moved is located. The point where the force is applied to move the load is the point of effort. The closer the fulcrum is to the load, the less effort it takes to move the load.

A wheel is a cylindrical object that rotates about the axis of the cylinder. The axle is a rígid rod that goes through the center of the wheel and lies along the cylinder axis. The wheel and axle are dealt with as a single unit when they are rigidly joined to each other and work together as a unit.

Something about atoms

All the millions of substances in the world are built out of only about a hundred simple substances. We call these sim­ple substances elements. The very smallest bit of an element is an atom. Iron, for instance, is one of the elements. The very smallest bit of iron is an atom of iron.

Atoms are so tiny that it is hard to imag­ine how tiny they are. The ink in the period at the end of this sentence has more atoms in it than there are people in the whole world. In a thimbleful of air there are more atoms than you could count if you lived to be a million years old. Of course, atoms are too small to be seen even with powerful microscopes. We know about them only from the way they act.

What is lava?

Lava is red-hot liquid rock which comes from deep within the earth and breaks through the top of a volcano when it erupts. Millions of years ago the Earth had many volcanoes. As a result, much of the rock on the Earth today is hardened lava.

Lava may seep slowly out and cool quickly, or it may burst forth violently and pour at the rate of 40 miles an hour over fields, forests and villages.

The lava hardens in swirls and ripples like petrified molasses. It may pour over a cliff and harden into a solid waterfall. If the surface of lava cools and hardens while that beneath continues to flow, lava caves are created. Lava stalactites and stalagmites, twisted, corded and very fragile, may be found within the caves.

What is kinetic theory?

The kinetic theory applies to liquids, gases, and solids. The explanation of the kinetic theory, however, is best illustrated in gases.

The kinetic theory assumes that all gases are made up of tiny particles called molecules. The distance separating the molecules from one another is very large compared to the size of the molecules themselves. The theory also assumes that the molecules are in a constant state of motion, except at absolute zero. Because they are in mo­tion, they collide with one another and with the walls of any container. The collisions with the walls cause pressure to be exerted on the container. The molecules are assumed to be perfectly elastic so that when they collide, they rebound without any loss of energy. The velocity of the molecules depends on the temperature. As the temperature increases, the velocity of the particles increases.

What is a cell?

All living things—lions, butterflies, grass, elm trees, dogs, people, and everything else alive—are built of cells. There are millions of cells in the bodies of most plants and animals. Some plants and ani­mals, however, are made up of just one cell.

Not all cells are the same shape or size. Some, such as red blood cells, are disk-shaped while others, such as muscle cells, are long and narrow. Nerve cells have very irregular shapes. Some plant cells are brick-shaped while others are round. There are many other shapes of both plant and animal cells, too. Most cells are far, far too small to be seen without a microscope. Some are just barely large enough to be seen with the naked eye. And some, because of the food stored in them, are rather large. The yolk of a newly formed hen's egg, for instance, is a cell.

Different kinds of cells do different kinds of work. Certain animal cells carry messages. Others carry oxygen. Some fight diseases. Still others make the animal move. Some plant cells take in water. Some manu­facture food, and so on.

Interesting facts about the aye-aye

• The aye-aye (Daubentonia madagascariensis) is a furry animal the size of a cat.
• The aye-aye is one of the lemurs, relatives of the monkeys.
• The name aye-aye comes from the sound it makes.
• The aye-aye is a strepsirrhine primate native to the island of Madagascar.
• This primate is not common even on this island. Besides, it comes out of hiding only at night.
• The aye-aye is the world's largest nocturnal primate.
• Its binomial name, Daubentonia madagascariensis, honours the French naturalist Louis-Jean-Marie Daubenton and the island on which it is found, Madagascar.
• With its big eyes and long fingers, an aye-aye looks rather frigthtening at night. But the natives of Madagascar would not think of killing one of these small animall. They believe that a person who kills an eye-eye is sure to die within a year himself.
• From an ecological point of view the aye-aye fills the niche of a woodpecker as it is capable of penetrating wood to extract the invertebrates within.

The first automobiles

Henry Ford's first car

The idea of using an engine of some kind to turn the wheels of a carriage is really quite old. The first automobile accident happened in 1769, nearly 250 years ago. A steam carriage built by the Frenchman Nicolas Cugnot overturned on a curve. It was traveling less than three miles an hour!

In 1831 steam carriages carrying 18 passengers were making regular trips between cities in England. They averaged about five miles an hour. But toll road keepers began raising their rates on steam carriages. People sometimes threw stones at the car­riages. The government also began passing laws against them. One of these laws, called the Red Flag law, said that a man had to walk in front of any steam carriage and carry a red flag during the day or a red lantern at night. All these factors kept the steam carriages from becoming very popular in England.

In Germany, a few years later, men developed new ideas about engines. Nikolaus Otto made an engine in 1876 that worked very much like a modern gasoline engine. In 1885 Gottlieb Daimler successfully mounted a small model of this engine on a bicycle. This engine burned kerosene. In that same year another German, Karl Benz, built a three-wheel car that was driven by a gasoline engine. The modern car grew out of many of these older ideas.

The first gasoline car in the United States was built in 1892 by Charles and Franklin Duryea of Springfield, Mass. It was a buggy with a two-cylinder engine fastened to the back axle. The Duryeas were not satisfied with this car, however, and the next year they made a better one. Very soon afterward Elwood Haynes, R. E. Olds, Henry Ford, and others had built cars.