Enough sleep is important to health. The amount of sleep needed depends on the age of the person and the conditions in which sleep takes place. The young may need more sleep than the old, but usually eight hours are enough for the health of grown-ups. Some can do with less than this amount, but others may need more. Every person knows his own need. It is then a matter of good judgement to satisfy his need. Sleep should always be enough to make one bring back his strength and get ready for a day's work.

    Fresh air is necessary to sound sleep. It is not without reason for some people to think that it is practicable to sleep in the open air. When one can keep himself warm, out-of-door sleeping probably gives the body its most complete relaxation (放松).

    Ability (能力) to sleep lies largely in habit. The conditions referred to only lead to sleep. Out-of-door exercises, a good habit of regular hours and the avoidance (避免) of late eating and worry, which are largely within the control of any person, are all helpful to sound sleep.

    A bath at bedtime, neither hot nor cool but of body temperature may be helpful to sleep. Sleep-producing drug (药) should never be taken except when suggested by a doctor.

China is a land of bicycles. At least it was back in 1992 when I traveled the country. Back then everyone seemed to be riding a bicycle. Millions of them, all black. Cars were rare. Yet since my arrival in Beijing last year, I've found the opposite is true. There are millions of cars. However, people still use their bicycles to get around. For many, it's the easiest and cheapest way to travel today. Bicycles also come in different colors—silver, green, red, blue, yellow, whatever you want.

    It's fun watching people biking. They rush quickly through crossroads, move skillfully through traffic, and ride even on sidewalks(人行道). Bicycles allow people the freedom to move about that cars just can't provide.

    Eager to be part of this aspect of Chinese culture, I decided to buy a bicycle. Great weather accompanied (伴随) my great buy. I immediately jumped up on my bicycle seat and started home.

    My first ride home was orderly(守秩序的). To be safe, I stayed with a large group of bikers while cars on the streets came running swiftly out of nowhere at times. I didn't want to get hit. So I took the ride carefully.

    Crossing the streets was the biggest problem. It was a lot like crossing a major highway back in the United States. The streets here were wide, so crossing took time, skill and a little bit of luck.

    I finally made it home. The feeling on the bicycle was amazing. The air hitting my face and going through my hair was wonderful. I was sitting on top of the world as I passed by places and people. Biking made me feel alive.

    Winter is the perfect time to see Washington in a different light. The crowds have thinned, and those humid 95-degree days are long gone. And the National Zoo is a different experience because of 500,000 bulbs that illuminate the annual Zoo-lights celebration.

    Eco-friendly twinkly lights will decorate zoo walkways, trees and buildings. Sculptures featuring popular zoo residents, including elephants and giant pandas, light up in time to music.

    If walking and watching isn't enough excitement, head to Lion & Tiger Hill, home to a 150-foot-long snow-less tubing run. Rides on the trackless train and the carousel also will be available.

    Don't forget to visit a few of the zoo's real animals. The Kids' Farm, Reptile Discovery Center, Small Mammal House, Think Tank (orangutans) and Great Cats exhibit will be open in the evening. There's no guarantee, however, that the animals will be as lively as the humans in attendance.

    When: Friday to January 1 (except December 24-25), 5 to 9 p.m.

    Where: 3001 Connecticut Ave. NW, Washington, D.C.

    How much: Admission is free; limited parking is $22. Charges for tubing, train rides and carousel rides.

    For more information: A parent can visit nationalzoo.si.edu/events/zoolights.

    More ZooLights celebrations: For those outside of the D.C. area, here are some links to other zoos with similar events (not all are free):

    Columbus Zoo, Ohio: Through January 1.

    Detroit Zoo, Michigan: Through December 31.

    Denver Zoo, Colorado: December 2-January 1.

    Houston Zoo, Texas: Through January 15.

    Three men have had a big influence on modern sound and communication technologies. We started with the beginnings of computer-generated music.

Max Vernon Mathews

    Max Vernon Mathews has been called the father of computer music. He created electronic tools so that people could use computers, as musical instruments. He had a huge influence on the development of electronic music and how it is written, recorded and played. In 1957, Max wrote the first: computer program, Music, to enable a computer to create sound and play it back. The computer was so slow that it would have taken an hour to play the piece of music in seventeen seconds. For that reason, Mathews moved the work to a tape player, which could be sped up to play the music at a normal speed.

    Mathews continued creating other versions of the Music program. He became interested in how computers could help musicians outside recording studios. The Groove program he developed was the first computer program made for live performances.

Norio Ohga

    Sony Corporation official Norio Ohga helped to develop, the compact disc in the late 1970s.

    He pushed for CDs to be larger, and with a longer playing time. He wanted them to hold seventy-five minutes so that they could store all of Bcethoven's Ninth Symphony on one disc. This way, listeners could enjoy the musical work without any break. The compact disc changed the electronics industry and the way people listened to music.

Hubert Joseph Schlafly

    Hubert Joseph Schlafly was an electrical engineer who helped change the way actors, politicians and other people speak on television. In 1950, he and two other men developed the teleprompter. One co-worker, Fred Barton, was an actor. He had an idea for a tool that would help television actors read their lines without having to memorize them. The first teleprompter involved a person who turned a long piece of paper printed with tall letters. As the actor read the lines, another person would, move the paper ahead on the device. Later versions used television screens to show the words that were to be read.

    Grown-ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play, catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins "Twinkle, twinkle, little star" or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, extra learning trials (尝试) increase the length of time we will remember it.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as "Twinkle, twinkle, little star" and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables (乘法口诀表) are an exception (例外) to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood.

The law of overlearning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.

    In the mid-1990s, Tom Bissell taught English as a volunteer in Uzbekistan. He left after seven months, physically broken and having lost his mind. A few years later, still attracted to the country, he returned to Uzbekistan to write an article about the disappearance of the Aral Sea.

    His visit, however, ended up involving a lot more than that. Hence this book, Chasing the Sea: Lost Among the Ghosts of Empire in Central Asia, which talks about a road trip from Tashkent to Karakalpakstan, where millions of lives have been destroyed by the slow drying up of the sea. It is the story of an American travelling to a strange land, and of the people he meets on his way: Rustam, his translator, a lovely 24-year-old who picked up his colorful English in California, Oleg and Natasha, his hosts in Tashkent, and a string of foreign aid workers.

    This is a quick look at life in Uzbekistan, made of friendliness and warmth, but also its darker side of society. In Samarkand, Mr Bissell admires the architectural wonders, while on his way to Bukhara he gets a taste of police methods when suspected of drug dealing. In Ferghana, he attends a mountain funeral(葬礼)followed by a strange drinking party. And in Karakalpakstan, he is saddened by the dust storms, diseases and fishing boats stuck miles from the sea.

    Mr Bissell skillfully organizes historical insights and cultural references, making his tale a well-rounded picture of Uzbekistan, seen from Western eyes. His judgment and references are decidedly American, as well as his delicate stomach. As the author explains, this is neither a travel nor a history book, or even a piece of reportage. Whatever it is, the result is a fine and vivid description of the purest of Central Asian traditions.