Tahukah Anda/Did You Know?

chiKenliTeL

The Bank of America started as the Bank of Italy

Amedeo Giannini, son of Italian immigrants to the US, started the Bank of America in a converted saloon in San Francisco at 9 am on Monday, 17 October 1904. On the first day, 28 deposits totalled $8,780.

When an earthquake struck in 1907, he ran his bank from a plank in the street. Word quickly spread about his service and by 1916 he had several branches. By 1929, the bank was strong enough to withstand the Great Depression stock crash. Giannini changed the name to Bank of America in 1928 and remained chairman until 1963.

The Bank of Italy in Italy was created in 1893 through the merger of 3 of the 6 banks at the time: Banca Nazionale nel Regno d'Italia and 2 Tuscan banks.

The Bank of England was founded by William Patterson after King William III of England found himself badly in need of funds to fight a war with France in 1694. Patterson provided the funds after the king agreed to order all the goldsmiths of London to stop issuing receipts as depositories for precious metals, forcing merchants to store their gold with the new bank. The Bank of England was finally authorised in 1946.

The Reichsbank of Germany was founded by Meyer Amschel Rothschild (1743-1812), who appointed his son Karl over the Bank of Naples, and his son Salomon over the Bank of Vienna. Later, his son Edmund presided over the Bank of Germany,and his son Nathan over the Bank of England.

chiKenliTeL

The can opener was invented 48 years after cans were introduced

Cans were opened with a hammer and chisel before the advent of can openers. The tin cannister, or can, was invented in 1810 by a Londoner, Peter Durand. The year before, French confectioner, Nicolas Appert, had introduced the method of canning food (as it became known) by sealing the food tightly inside a glass bottle or jar and then heating it. He could not explain why the food stayed fresh but his bright idea won him the 12,000-francs prize that Napoleon offered in 1795 for preserving food. Durand supplied the Royal Navy with canned heat-preserved food while Appert would help Napoleon's army march on its stomach.

Tin canning was not widely adopted until 1846, when a method was invented to increase can production from 6 in an hour to 60. Still, there were no can openers yet and the products labels would read: "cut around on the top near to outer edge with a chisel and hammer."

The can opener was invented in 1858 by American Ezra Warnet. There also is a claim that Englishman Robert Yeates invented the can opener in 1855. But the can opener did not become popular until, ten years later, it was given away for free with canned beef.

The well-known wheel-style opener was invented in 1925. Beer in a can was launched in 1935. The easy-open can lid was invented by Ermal Cleon Fraze in 1959.

Since 1972, some 64 million tons of aluminum cans (about 3 trillion cans) have been produced. Placed end-to-end, they could stretch to the moon about a thousand times. Still, cans represent less than 1% of solid waste material - about one quarter of all cans are recycled. Worldwide, some 9 million cans are recycled every hour. Which is good news, considering that it takes a can about 200 years to degrade if you bury it. It takes paper about a month to bio-degrade, a woolen sock about a year, and plastic hundreds of years.

chiKenliTeL

There are about a billion bicycles in the world

There are about a billion bicycles in the world, twice as many as motorcars. Almost 400 million bicycles are in China.

Although Leonardo da Vinci drew some rough sketches of a contraption that looked like a bicycle, the Frenchman De Sivrac built the first bicycle-type vehicle in 1690. It was referred to as a hobbyhorse. However, it did not have pedals. Those were added in 1840 by a Scottish blacksmith, Kirkpatrick Macmillan, who is credited with inventing the real bicycle.

The bicycle as we know it today - with two wheels of the same size - looks almost exactly the same as one from 1900.

The world speed record on a bicycle is held by John Howard of the US. In 1985 he reached 245,08 km/h (154 mph), cycling in the slipstream of a specially designed car.

Air-filled tyres were used on bicycles before they were used on motorcars.

zalliza1717

Tahukah anda...

1. Apabila anda berdiri sambil mendepakan tangan anda,jarak di antara hujung tangan kanan anda hingga ke hujung tangan kiri adalah bersamaan dgn tinggi anda.. tak caya :hmm: ..cubalah ukur sendiri..

2.Panjang dari pergelangan tangan hingga ke pelipat siku adalah sama dengan saiz tapak kaki anda yer ker..cuba ler angkat kaki dan letak tapak kaki anda di ats lengan,amacam..sama panjang tak?

3.Gas yang anda keluarkan ( kentut :bgrin: ) adalah hidrogen sulfida,H2S, iaitu gas yg sama dgn bau telur tembelang..(telur busuk)

4.Bau hancing air kencing adalah bau ammonia

5.Kita selalu dengar perkataan 'hujan asid'..tapi tahukah anda apakah jenis asid itu?
-Kalau di kawasan bandar,biasanya hujan asid adalah asid nitrik,HNO3..kenapa..sebab terhasil daripada gas NO2 yg dikeluarkan oleh asap kenderaan manakala di kawasan industri,hujan asid biasanya adalah asid sulfurik,terhasil daripada pembebasan sulfur dioksida,SO2 oleh kilang2..

6.Apakah warna sebenar air laut?..biru?:stp:
-warna biru air laut adalah disebabkan oleh pantulan warna biru dari langit..iaitu warna dari lapisan ozon..sebenarnya langit yg berwarna biru,bukannya laut..itulah sebab kenapa bila ari nak hujan,air laut pun dah tak biru..

7.Sebut pasal ozon,O3,bau ozon sebenarnya boleh dibau.. tp mcmana ek bau ozon?
cuba anda pergi ke tengah padang yang luas dan lapang selepas hujan berhenti,bau seakan2 tengik itu adalah bau ozon..

***info ini bukannya di "copy" dari internet atau mana2 majalah,ini adalah hasil ilmu belajar time undergrad kat UTM dulu,kalau ada persamaan,itu adalah kebetulan***

chiKenliTeL

The modern toilet was invented by a watchmaker

It is often incorrectly quoted that the toilet was invented by a Mr Thomas Crapper in the 18th century. Actually, simple toilets have been used since Babylonian times. In 1596, John Harrington invented an indoor water closet for Queen Elizabeth I. But Harrington then published a book with tasteless puns about his own invention. The toilet then dropped into obscurity for nearly 200 years. In 1775, London watchmaker Alexander Cummings patented the forerunner of today's toilet.

There was a Mr Crapper around at the time - he happened to be a successful plumber, appropriately.

The British word for toilet, "loo", derives from the French "garde a l'eau!" In medieval Europe people had little conception of hygene and threw the contents of their chamber pots out the window into the street below. In France the practice was preceded by "garde a l'eau!" ("watch out for the water!";). In England, this phrase was Anglicised, first to "gardy-loo!", then just "loo", and eventually came to mean the toilet/lavatory itself. The American word for toilet, "john", is called after the John Harington mentioned above.

In 1913, the Russian airline became the first to feature a toilet on board. The movie Psycho is said to be the first film to show a toilet being flushed. Toilet paper is thought to have been introduced in China at around 850, long before the advent of the toilet as we know it.

Were the Wright Brother really the first to fly?

guynextdoor

Originally posted by zalliza1717 at 10-2-2007 08:20 PM
Tahukah anda...

6.Apakah warna sebenar air laut?..biru?
-warna biru air laut adalah disebabkan oleh pantulan warna biru dari langit..iaitu warna dari lapisan ozon..sebenarnya langit yg berwarna biru,bukannya laut..itulah sebab kenapa bila ari nak hujan,air laut pun dah tak biru..
...

then.. zalliza dear,
my next爍uestion爐o爕ou燵color=#0000ff]why爄s爐he爏ky燽lue?爇alau燽ole爅awab燿alam

zalliza1717

langit biru adalh disebabkan oleh lapisan ozon

zalliza1717

tahukah anda...

1.Kenapa bila time kita sakit,gi amik ubat, kat ubat tu selalu tulis '1 biji SELEPAS makan' dan kadang2 kita dpt ubt dia tulis '1 biji SEBELUM makan'......apa beza kene amik SEBELUM @ SELEPAS?
-Sebab kat dalam perut kita ni ada asid,asid hidroklorik,HCl,kalau time kita lapar (perut kosong) tahap keasidan di dalam perut adalah tinggi..tu selalu pedih perut kalau perut kosong..bila ubt suruh amik SEBELUM mkn,itu maksudnya ubat tersebut larut di dalam asid,bukan di dalam air..begitu lah juga sebaliknya..kalau ubt kene amik SELEPAS mkn maksudnya ubt tu hanya larut di dlm air..so ikut lah peraturan mkn ubt yg betul..kalau tak sia2 jer amik ubt,tp ubt tak dissolve pun..heheh..

2.Masih lagi bab ubat,kenapa mkn ubt kene ngan air putih (air masak)..tak leh teh,kopi,susu n etc?
-kalau amik ngan :
susu-- susu mengandungi kalsium,kalsium akan melambatkan penyerapan ubat
teh,kopi -- minuman ni mengandungi kafein yg akan menghalang penyerapan ubt dgn lebih efektif
juice --- juice mengandungi serat yang fungsi dia pun sama mcm kat atas

3.Kadang2 kita selalu terkena mata terkelip2..org tua2 selalu kata kalau terkelip sblh kanan,nk dgr berita gembira n kalau sebelah kiri nak menangis..kenapa sebenarnya ek?
-mengikut istilah sains,sindrom mata terkelip ni menunjukkan bdn kita kekurangan kalsium dan magnesium...

4.Org tua2 selalu pesan,mkn nasi jgn berulam kan air,tak baik...tapi bila dtanya kenapa tak baik diorng pun tak leh bg tau apa yg tak baiknya..kan?
-Dari segi sains,bila mkn berulamkan air ,air akn menyebabkan tahap keasidan di dalam perut menjadi cair sekali gus mengurangkan tahap kecekapan perut kita utk mencerna makanan,bila makanan yg tak dicerna sepenuhnya akan menghasilkan gas ,dalam bahasa kampungnya..akan menyebabkan perut kembung..

waterboy

ha...baru sesuai post kat sini....teruskan ya......:clap: :pompom:

chiKenliTeL

ye ke? bukan ke pasal dia memang biru2 gitu ~~~

chiKenliTeL

Predictions that missed the mark

In 1894, the president of the Royal Society, Lord Kelvin, predicted that radio had no future. The first radio factory was opened five years later. He also predicted that heavier-than-air flying machines were impossible. Today, there are more than one billion radio sets in the world, tuned to more than 33 000 radio stations around the world. The Wright Brother's first flight covered a distance equal to only half the length of the wingspan of a Boeing 747.

In the early 20th century a world market for only 4 million automobiles was made because "the world would run out of chauffeurs." Shortly after the end of World War II (1945), the whole of Volkswagen, factory and patents, was offered free to Henry Ford II. He dismissed the Volkswagen Beetle as a bad design. Today, more than 70 million motorcars are produced every year. The Beetle became one of the best-selling vehicles of all time.

The telephone was not widely appreciated for the first 15 years because people did not see a use for it. In fact, in the British parliament it was mentioned there was no need for telephones because "we have enough messengers here." Western Union believed that it could never replace the telegraph. In 1876, an internal memo read: "This telephone has too many shortcomings to be seriously considered as a means of communication." Even Mark Twain, upon being invited by Alexander Graham Bell to invest $5 000 in the new invention, could not see a future in the telephone.

Irish scientist, Dr. Dionysius Lardner (1793 - 1859) didn't believe that trains could contribute much in speedy transport. He wrote: "Rail travel at high speed is not possible, because passengers ' would die of asphyxia' [suffocation]." Today, trains reach speeds of 500 km/h.

In 1943, Thomas Watson, the chairman of IBM forecast a world market for "maybe only five computers." Years before IBM launched the personal computer in 1981, Xerox had already successfully designed and used PCs internally... but decided to concentrate on the production of photocopiers.

In 1894, A.A. Michelson, who with E.W. Morley seven years earlier experimentally demonstrated the constancy of the speed of light, said that the future of science would consist of "adding a few decimal places to the results already obtained."

chiKenliTeL

Cows don't have upper front teeth

Although a cow has no upper front teeth, it grazes up to 8 hours a day, taking in about 45 kg (100 lb) of feed and the equivalent of a bath tub full of water. A healthy cow gives about 200,000 glasses of milk in her lifetime.

A cow has four stomachs: the rumen, reticulum, omasum and abomasum. The rumen is the largest stomach and acts as a fermentation chamber. The abomasum is last of the four and is comparable in both structure and function to the human stomach.

With all its grazing and many stomachs, it is no wonder that cows are one of the main contributors to the hole in the ozone layer. Apart from CFC, the biggest culprit is hydrocarbon emissions from cars and cows. Yes, cows! Cows release some 100 million tons of hydrocarbon annually - by releasing gas. To give you an idea of how much gas a cow emits: if the gas of 10 cows could be captured, it would provide heating for a small house for a year.

But unlike what you think, cows release hydrocarbon mostly by burping.

chiKenliTeL

The World's Largest Rough Diamonds


Cullinan - 3,106.75 carats - 1905, South Africa
Excelsior - 995.20ct. - 1893, South Africa
Star of Sierra Leone - 968.80ct. - 1972, Sierra Leone
Zale - 890.00ct. - 1984, Africa
Great Mogul - 787.50ct. - 1650, India
Woyie River - 770.00ct. - 1945, Sierra Leone
Presidente Vargas - 726.60ct. - 1938, Brazil
Jonker - 726.00ct. - 1934, South Africa
Reitz - 650.80ct. - 1895, South Africa
Unnamed - 620.14ct. - 1984, South Africa

chiKenliTeL

What is it called?


The practice of eating insects is called entomophagy
Most insects are edible. According to eatbug.com, there are 1,462 recorded species of edible insects. And they're quite nutritious. For instance, 100 grams of cricket contains only 121 calories, less than half of beef. A cricket contains only 5,5 grams of fat, compared to 21,2g of beef. Beef contains more protein (23,5g - a cricket 12.9g) but the 100g of cricket also contains 5,1g of carbohydrates, 75,8 mg calcium, 185,3 mg phosphorous, 9,5 mg iron, thiamin, riboflavin, and niacin.

Mid-men, the male versions of mid-wives, are called accouchers.

The working section of a piano is called the action.

The plastic things on the end of shoelaces are called aglets.

The distance that a place holder falls from a glass when it is lifted (you know, place holders sometimes get stuck to the bottom of a cold glass when you lift the glass) is called a bevemeter.

The study of creatures such as Bigfoot, the chupacabra, and the Loch Ness monster is called cryptozoology. Zoologist Bernard Heuvelmans coined the term to describe his investigations of animals unknown to science.

The apparatus used in alcohol distilleries for freeing the spirit from water is called the dephlegmator.

One that speaks two languages - is bilingual - can be said to be diglot.

Ducks are never male. The males of the species are called drakes.

Shoemakers are commonly called cobblers but correctly speaking a cobbler is a shoe repairmen. A shoemaker is a cordwainer.

The device at the intersection of two railroad tracks to permit the wheels and flanges on one track to cross or branch for the other is called a frog.

A specific length of thread or yarn according to the type of fiber is called a hank. For linen, a hank is 274 metres (300 yards); for cotton, it is 768 metres (840 yards).

The white part of your fingernail is called the lunula.

The thin line of cloud that forms behind an aircraft at high altitudes is called a contrail.

A depth of 2 fathoms (3,6 metres) is called a Mark Twain. Originally a fathom was the space reached by with two arms outstretched.

In the early days of film making, people who worked on the sets were called movies. The films were called potion pictures.

The tendency of the leaves or petals of certain plants to assume a different position at night is called nyctitropism.

The back of the human hand is the opisthenar.

Someone who uses as few words as possible when speaking is called pauciloquent.

People that study fish are called ichthyologists.

The pin that holds a hinge together is called a pintle.

The gland responsible for producing the hormone that regulates growth is called the pituitary gland. It is the size of a pea.

A melody is a group of notes in a certain order that results in a sweet or agreeable sound. An easily remembered melody is called a tune.

Compulsive shopping was identified by a German psychiatrist almost a hundred years ago. Clinically it is known as oniomania. Shopaholics are the people who do not suffer from chrematophobia, which is the fear of touching money. Also see phobias

In early France the distance a man could walk while smoking one pipeful of tobacco was called a pipee.

The central shaft of a bird's feather which bears the vane or web of the feather is called a rachis.

The hairless area of roughened skin at the tip of a bear's snout is called the rhinarium.

Someone who habitually picks their nose is called a rhinotillexomaniac (rhino=nose, tillexis=habit of picking at something, mania=obsession with something). See Useless Information

A building in which silence is enforced, like a library or school room, is referred to as a silentium.

The ear-splitting sound produced by the high notes of a bagpipe is called a skirl.

The fleshy projection above the bill on a turkey is called a snood.

People who chase after rare birds are called twitchers.

4 gills of ale and beer is 1 pint, 2 pints = 1 quart, 4 quarts = 1 gallon, 9 gallons = 1 firkin, 2 firkins = 1 kilderkin, 3 kilderkins = 1 hogshead, 2 hogsheads = 1 butt.

chiKenliTeL

Why does wet fabric appear darker?
When fabric gets wet, light coming towards it refracts within the water, dispersing the light. In addition, the surface of the water causes incoherent light scattering. The combination of these two effects causes less light to reflect to your eyes and makes the wet fabric appear darker.

Why does water not calm the tongue after eating hot spicy food?
The spices in most of the hot foods that we eat are oily, and, like your elementary school science teacher taught you, oil and water don't mix. In this case, the water just rolls over the oily spices.
What can you do to calm your aching tongue? Eat bread. The bread will absorb the oily spices. A second solution is to drink milk. Milk contains a substance called "casein" which will bind to the spices and carry them away. Alcohol also dissolves oily spices.

Why is blue for boys and pink for girls?
In ancient times, it was believed that certain colours could combat the evil spirits that lingered over nurseries. Because blue was associated with the heavenly spirits, boys were clothed in that colour, boys then being considered the most valuable resource to parents. Although baby girls did not have a colour associated with them, they were mostly clothed in black. It was only in the Middle Ages when pink became associated with baby girls.

Why do people kiss under the mistletoe at Christmas?
In ancient myth, when the son of the Norse goddess Frigga was killed by an arrow made of mistletoe and then brought back to life, she blessed the mistletoe and bestowed a kiss on all who passed beneath it. In the 18th century, the legend was adopted as a promise to marry. At Christmas a lady standing under a mistletoe may not refuse a kiss. If she does, she cannot expect to marry the following year. So it is told.

Why are there bunnies and eggs at Easter?
The ancient Anglo-Saxons celebrated the return of spring with a carnival commemorating their goddess of offspring and of springtime, Eostre. The word carnival possibly originated from the Latin ‘carne vale' meaning "flesh, farewell" or "meat, farewell." The offerings were rabbits and coloured eggs, bidding an end to winter.
As it happened, the pagan festival of Eostre occurred at the same time of year as the Christian observance of the Resurrection of Christ and it didn't take the Christian missionaries long to convert the Anglo-Saxons when they encountered them in the second century. The offering of rabbits and eggs eventually became the Easter bunny and Easter eggs.

If blood is red, why are veins blue?
Blood is bright red in its oxygenated form and a dark red in deoxygenated form. In simpler terms, it is bright red when it leaves the lungs full of oxygen and dark red when it returns to the lungs for a refill. Veins appear blue because light penetrating the skin is absorbed and reflected in high energy wavelengths back to the eye. Higher energy wavelengths are blue.

Why did Columbus and others try to sail around the world?
You probably know that people native to the Americas are called "Indians" because early explorers like Christopher Columbus thought they had come across the Indian spice islands. Traders were forced to sail westward after the spice route to the East by land was blocked for Europeans by Muslim uprisings.

Why is it called a "loo?"
The British word for toilet, "loo", derives from the French "garde a l'eau!" In medieval Europe people had little conception of hygiene and threw the contents of their chamber pots out the window into the street below. In France the practice was preceded by "garde a l'eau!" ("watch out for the water!"). In England, this phrase was Anglicised, first to "gardy-loo!", then just "loo", and eventually came to mean the toilet/lavatory itself. The American word for toilet, "john", is called after the John Harington who in 1596 invented an indoor water closet for Queen Elizabeth I.

Why is the sky blue?
When sunlight travels through the atmosphere, it collides with gas molecules. These molecules scatter the light. The shorter the wavelength of light, the more it is scattered by the atmosphere. Because it has a shorter wavelength than the other colours, blue light is scattered more, ten times more than red light, for instance. That is why the sky is blue.
Why does the setting sun look reddish orange? When the sun is on the horizon, its light takes a longer path through the atmosphere to reach your eyes than when the sun is directly overhead. By the time the light of the setting sun reaches your eyes, most of the blue light has been scattered out. The light you finally see is reddish orange, the colour of white light minus blue.

Why do onions make you cry?
Onions, like other plants, are made of cells. The cells are divided into two sections separated by a membrane. One side of the membrane contains an enzyme which helps chemical processes occur in your body. The other side of the membrane contains molecules that contain sulfur. When you cut an onion, the contents on each side of the membrane mix and cause a chemical reaction. This reaction produces molecules such as ethylsufine which make your eyes water.
To prevent crying when you cut an onion, cut it under a running tap of cold water. The sulfur compounds dissolve in water and are rinsed down the sink before they reach your eyes. You can also put the onion in the freezer for ten minutes before you cut it. Cold temperatures slow down the reaction between the enzyme and the sulfur compounds so fewer of the burning molecules will reach your eyes.

Why are camels called "ships of the desert?"
Camels are called "ships of the desert" because of the way they move, not because of their transport capabilities. Camels sway from side to side because they move both legs on one side at the same time, elevating that side. This is called pacing, a ship-like motion which can make the rider feel sick.

Why you shouldn't smoke
If you smoke, you're also inhaling arsenic, benzene, cadmium, hydrogen cyanide, lead, mercury and phonol. In all, 4 000 harmful chemicals, including 44 types of poison, of which 43 are proven cancer-causing substances. Read the full story

aku_EnSeM

simbol integration (pengamiran) yg macam ular tu dtang dari huruf 'S', iaitu jumlah, merujuk kepada jumlah luas di bawah graf...

me_ai

The International Space Station is the largest and most complex international scientific project in history. And when it is complete just after the turn of the century, the the station will represent a move of unprecedented scale off the home planet. Led by the United States, the International Space Station draws upon the scientific and technological resources of 16 nations: Canada, Japan, Russia, 11 nations of the European Space Agency and Brazil.

More than four times as large as the Russian Mir space station, the completed International Space Station will have a mass of about 1,040,000 pounds. It will measure 356 feet across and 290 feet long, with almost an acre of solar panels to provide electrical power to six state-of-the-art laboratories.

The station will be in an orbit with an altitude of 250 statute miles with an inclination of 51.6 degrees. This orbit allows the station to be reached by the launch vehicles of all the international partners to provide a robust capability for the delivery of crews and supplies. The orbit also provides excellent Earth observations with coverage of 85 percent of the globe and over flight of 95 percent of the population. By the end of this year, about 500,000 pounds of station components will be have been built at factories around the world.

me_ai

ISS on 1999


ISS on 2006


Different module and staggered development of the ISS

Destiny,  Zarya, Zvezda,  Laboratory(node 1) Module 2001
Since 2000, the only main pressurized module delivered to the ISS was the Destiny Laboratory Module by STS-98 in 2001. The US Lab was also the first science module delivered to the ISS, whereas Zarya provides electrical power, storage, propulsion, and guidance functions and Zvezda provides living quarters, a life support system, a communication system, electrical power distribution, a data processing system, a flight control system, and a propulsion system. Node 1's primary function is to link different modules together, however fluids, environmental control and life support systems, electrical and data systems are also routed through Node 1 to supply work and living areas of the station

A total of 10 main pressurized modules (Zarya, Zvezda, Destiny, Unity Module -also called Node 1-, Node 2, Node 3, Columbus, Kibo, MLM and the RM) are currently scheduled to be part of the ISS by its completion date in 2010.[7] A number of smaller pressurized sections will be adjunct to them (Soyuz spacecrafts (permanently 2 as lifeboats - 6 months rotations), Progress transporters (2 or more), the Quest and Pirs Airlocks, as well as periodically the MPLM, the ATV and the HTV).

Multi Purpose Logistic Module (MPLM) August 2007


Harmony Node 2 Module 2007


Columbus Module 2008/2009


Kibo Module 2009


Cupola Module  2010


Research Module 2010 or later

taken from http://en.wikipedia.org/wiki/International_Space_Station

[ Last edited by  me_ai at 10-4-2007 01:18 PM ]

oobi

How Google Finds Your Needle in the Web's Haystack

As we'll see, the trick is to ask the web itself to rank the importance of pages...

by David Austin
Grand Valley State University

Imagine a library containing 25 billion documents but with no centralized organization and no librarians. In addition, anyone may add a document at any time without telling anyone. You may feel sure that one of the documents contained in the collection has a piece of information that is vitally important to you, and, being impatient like most of us, you'd like to find it in a matter of seconds. How would you go about doing it?

Posed in this way, the problem seems impossible. Yet this description is not too different from the World Wide Web, a huge, highly-disorganized collection of documents in many different formats. Of course, we're all familiar with search engines (perhaps you found this article using one) so we know that there is a solution. This article will describe Google's PageRank algorithm and how it returns pages from the web's collection of 25 billion documents that match search criteria so well that "google" has become a widely used verb.

Most search engines, including Google, continually run an army of computer programs that retrieve pages from the web, index the words in each document, and store this information in an efficient format. Each time a user asks for a web search using a search phrase, such as "search engine," the search engine determines all the pages on the web that contains the words in the search phrase. (Perhaps additional information such as the distance between the words "search" and "engine" will be noted as well.) Here is the problem: Google now claims to index 25 billion pages. Roughly 95% of the text in web pages is composed from a mere 10,000 words. This means that, for most searches, there will be a huge number of pages containing the words in the search phrase. What is needed is a means of ranking the importance of the pages that fit the search criteria so that the pages can be sorted with the most important pages at the top of the list.

One way to determine the importance of pages is to use a human-generated ranking. For instance, you may have seen pages that consist mainly of a large number of links to other resources in a particular area of interest. Assuming the person maintaining this page is reliable, the pages referenced are likely to be useful. Of course, the list may quickly fall out of date, and the person maintaining the list may miss some important pages, either unintentionally or as a result of an unstated bias.

Google's PageRank algorithm assesses the importance of web pages without human evaluation of the content. In fact, Google feels that the value of its service is largely in its ability to provide unbiased results to search queries; Google claims, "the heart of our software is PageRank." As we'll see, the trick is to ask the web itself to rank the importance of pages.

How to tell who's important

If you've ever created a web page, you've probably included links to other pages that contain valuable, reliable information. By doing so, you are affirming the importance of the pages you link to. Google's PageRank algorithm stages a monthly popularity contest among all pages on the web to decide which pages are most important. The fundamental idea put forth by PageRank's creators, Sergey Brin and Lawrence Page, is this: the importance of a page is judged by the number of pages linking to it as well as their importance.

We will assign to each web page P a measure of its importance I(P), called the page's PageRank. At various sites, you may find an approximation of a page's PageRank. (For instance, the home page of The American Mathematical Society currently has a PageRank of 8 on a scale of 10. Can you find any pages with a PageRank of 10?) This reported value is only an approximation since Google declines to publish actual PageRanks in an effort to frustrate those would manipulate the rankings.

Here's how the PageRank is determined. Suppose that page Pj has lj links. If one of those links is to page Pi, then Pj will pass on 1/lj of its importance to Pi. The importance ranking of Pi is then the sum of all the contributions made by pages linking to it. That is, if we denote the set of pages linking to Pi by Bi, then

This may remind you of the chicken and the egg: to determine the importance of a page, we first need to know the importance of all the pages linking to it. However, we may recast the problem into one that is more mathematically familiar. More here.

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