## What is a “perfect” number?

Approximately 2,500 years ago the Pythagoreans defined a “perfect” number as one for whom the sum of its divisors, excluding itself, equals the number itself. For example, 6 can be divided by 1, 2, 3, and 6. If you add these numbers together, excluding 6 itself, the total is 6. Therefore 6 is a perfect number. Over the centuries, many mathematicians from all over the world have contributed to finding and defining perfect numbers.

## When was the first post office in the United States established and how did the system grow?

Governor William Penn established Pennsylvania’s first post office in 1683. Central postal organization came to the colonies after 1692, when Thomas Neale received a 21-year grant from the British Crown, whose settlements dominated the Atlantic seaboard, for a North American postal system. It wasn’t until 1774, however, that William Goddard, a newspaper publisher and former postmaster, set up the Constitutional Post for intercolonial mail service.

Colonies funded it by subscription, and net revenues were used to improve mail service rather than to pay back to the subscribers. By 1775, when the Continental Congress met in Philadelphia, Goddard’s post was flourishing, and thirty post offices operated between Williamsburg, Virginia, and Portsmouth, New Hampshire. The Constitutional Post provided security for colonial messages and created a communication line that played a vital role in bringing about American independence during the Revolutionary War.

## What does it mean to be bilingual?

A bilingual person is able to speak two languages. A person who speaks more than two languages is called “multilingual.” A person does not have to speak two languages with equal fluency to be considered bilingual; usually, a person will be stronger in one language than another. It is common for most of the world’s societies to be multilingual; in the United States, one in five children enters school speaking a language other than English, according to the 2000 Census. Some children who learn English in school speak their native language at home. Bilingualism often allows children to communicate with their grandparents, which can strengthen family bonds across both generations and countries.

Bilingualism teaches an appreciation of the arts and traditions of two cultures. It promotes tolerance and cross-cultural understanding; research indicates that children who are raised with a bicultural identity tend to be more accepting of cultural differences in others.

## How long is each year?

Each calendar year is exactly 365 days, 5 hours, 48 minutes, and 46 seconds. This is the amount of time between two successive crossings of the celestial equator by the Sun at the vernal equinox (the first day of spring). The fact that the year is not a whole number of days has affected the development of calendars, which over time generate an error.

The current calendar we use, called the Gregorian calendar, attempts to fix this by adding an extra day to the month of February every four years. These years are called “leap years.”

## What did people use before toothbrushes were invented?

Early in human history, people used anything that they could find to keep their teeth clean. Usually a thin, sharp object, like a stick, was used to pick out food left between teeth. Chewing on the end of certain sticks would fray the wood, making a kind of brush, which could then be rubbed across the teeth. (Even today, members of primitive tribes chew sticks to keep their teeth clean. The constant chewing produces more saliva than usual, which helps wash food away.) Later, people found that if they rubbed abrasive elements, like salt or chalk, across their teeth, they could get rid of grime. They also used water and pieces of rough cloth to clean their teeth. Toothpicks made of all kinds of materials also became popular. Rich people had jeweled toothpicks made of gold and silver. Toothbrushes for the wealthy, with fancy handles and hog bristles, came into use in the eighteenth century.

Only much later, when cheaper, woodenhandled toothbrushes were made, and the importance of good dental hygiene became known, did most people start to regularly use them.

## How did we get the idea that the stork delivered babies?

The suggestion that storks delivered babies came from Scandinavia and was promoted by the writings of Hans Christian Andersen. Storks had a habit of nesting on warm chimneys and would often lift articles from clotheslines then stuff them into these nests, which to children looked like they were stuffing babies down the flue.

The stork is also very nurturing and protective of its young, which helped it become symbolic of good parenthood.

## What does it mean to “rest on your laurels”?

The practice of using laurels to symbolize victory came from the ancient Greeks. After winning on the battlefield, great warriors were crowned with a wreath of laurels, or bay leaves, to signify their supreme status during a victory parade.

Because the first Olympics consisted largely of war games, the champions were honoured in the same manner: with a laurel, a crown of leaves. To “rest on your laurels” means to quit while you’re ahead.

## How do birds replace their feathers?

Birds replace their feathers by molting, the periodic shedding of old feathers and the growing of new ones. They do this one to three times each year, although different birds molt at different times of the year. Male goldfinches, for example, molt from a dull greenish yellow to bright yellow during spring. The periodic shedding of feathers and their replacement with new ones makes perfect sense in the animal kingdom.

Feathers are incapable of further growth, and may get worn down, broken, and faded over the year from normal wear-and-tear. Molting replaces these damaged feathers and helps the males look attractive to females, which is why many molts take place during the mating season.

## What does the D stand for in D-Day?

Although D-Day has become synonymous with the Allied landing on June 6, 1944, in Normandy, it was used many times before and since. The D in D-Day simply stands for “day,” just as the H in H-Hour stands for “hour.” Both are commonly used codes for the fixed time when a military operation is scheduled to begin. “D minus thirty” means thirty days before a target date while “D plus fifteen” means fifteen days after.

## How many bones are there in the human body?

Babies are born with about 300 to 350 bones, but many of these fuse together between birth and maturity to produce an average adult total of 206. Bone counts vary according to the method used to count them, because a structure may be treated as either multiple bones or as a single bone with multiple parts. There are four major types of bones: long bones, short bones, flat bones, and irregular bones. The name of each type of bone reflects the shape of the bone. The shape of the bone also tells about its mechanical function. Bones that do not fall into any of these categories are sesamoid bones and accessory bones.